# DBM::Deep
#
# Description:
-# Multi-level database module for storing hash trees, arrays and simple
-# key/value pairs into FTP-able, cross-platform binary database files.
+# Multi-level database module for storing hash trees, arrays and simple
+# key/value pairs into FTP-able, cross-platform binary database files.
#
-# Type `perldoc DBM::Deep` for complete documentation.
+# Type `perldoc DBM::Deep` for complete documentation.
#
# Usage Examples:
-# my %db;
-# tie %db, 'DBM::Deep', 'my_database.db'; # standard tie() method
-#
-# my $db = new DBM::Deep( 'my_database.db' ); # preferred OO method
+# my %db;
+# tie %db, 'DBM::Deep', 'my_database.db'; # standard tie() method
#
-# $db->{my_scalar} = 'hello world';
-# $db->{my_hash} = { larry => 'genius', hashes => 'fast' };
-# $db->{my_array} = [ 1, 2, 3, time() ];
-# $db->{my_complex} = [ 'hello', { perl => 'rules' }, 42, 99 ];
-# push @{$db->{my_array}}, 'another value';
-# my @key_list = keys %{$db->{my_hash}};
-# print "This module " . $db->{my_complex}->[1]->{perl} . "!\n";
+# my $db = new DBM::Deep( 'my_database.db' ); # preferred OO method
+#
+# $db->{my_scalar} = 'hello world';
+# $db->{my_hash} = { larry => 'genius', hashes => 'fast' };
+# $db->{my_array} = [ 1, 2, 3, time() ];
+# $db->{my_complex} = [ 'hello', { perl => 'rules' }, 42, 99 ];
+# push @{$db->{my_array}}, 'another value';
+# my @key_list = keys %{$db->{my_hash}};
+# print "This module " . $db->{my_complex}->[1]->{perl} . "!\n";
#
# Copyright:
-# (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
-# This program is free software; you can redistribute it and/or
-# modify it under the same terms as Perl itself.
+# (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
+# This program is free software; you can redistribute it and/or
+# modify it under the same terms as Perl itself.
##
use strict;
}
$args = {@_};
}
- elsif ( ref $_[0] ) {
+ elsif ( ref $_[0] ) {
unless ( eval { local $SIG{'__DIE__'}; %{$_[0]} || 1 } ) {
$proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] );
}
$args = $_[0];
}
- else {
+ else {
$args = { file => shift };
}
}
sub new {
- ##
- # Class constructor method for Perl OO interface.
- # Calls tie() and returns blessed reference to tied hash or array,
- # providing a hybrid OO/tie interface.
- ##
- my $class = shift;
- my $args = $class->_get_args( @_ );
-
- ##
- # Check if we want a tied hash or array.
- ##
- my $self;
- if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) {
+ ##
+ # Class constructor method for Perl OO interface.
+ # Calls tie() and returns blessed reference to tied hash or array,
+ # providing a hybrid OO/tie interface.
+ ##
+ my $class = shift;
+ my $args = $class->_get_args( @_ );
+
+ ##
+ # Check if we want a tied hash or array.
+ ##
+ my $self;
+ if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) {
$class = 'DBM::Deep::Array';
require DBM::Deep::Array;
- tie @$self, $class, %$args;
- }
- else {
+ tie @$self, $class, %$args;
+ }
+ else {
$class = 'DBM::Deep::Hash';
require DBM::Deep::Hash;
- tie %$self, $class, %$args;
- }
+ tie %$self, $class, %$args;
+ }
- return bless $self, $class;
+ return bless $self, $class;
}
sub _init {
next unless exists $args->{$param};
$self->{$param} = delete $args->{$param}
}
-
+
# locking implicitly enables autoflush
if ($args->{locking}) { $args->{autoflush} = 1; }
-
+
$self->{root} = exists $args->{root}
? $args->{root}
: DBM::Deep::_::Root->new( $args );
#}
sub lock {
- ##
- # If db locking is set, flock() the db file. If called multiple
- # times before unlock(), then the same number of unlocks() must
- # be called before the lock is released.
- ##
+ ##
+ # If db locking is set, flock() the db file. If called multiple
+ # times before unlock(), then the same number of unlocks() must
+ # be called before the lock is released.
+ ##
my $self = $_[0]->_get_self;
- my $type = $_[1];
+ my $type = $_[1];
$type = LOCK_EX unless defined $type;
-
- if (!defined($self->_fh)) { return; }
-
- if ($self->_root->{locking}) {
- if (!$self->_root->{locked}) {
- flock($self->_fh, $type);
-
- # refresh end counter in case file has changed size
- my @stats = stat($self->_root->{file});
- $self->_root->{end} = $stats[7];
-
- # double-check file inode, in case another process
- # has optimize()d our file while we were waiting.
- if ($stats[1] != $self->_root->{inode}) {
+
+ if (!defined($self->_fh)) { return; }
+
+ if ($self->_root->{locking}) {
+ if (!$self->_root->{locked}) {
+ flock($self->_fh, $type);
+
+ # refresh end counter in case file has changed size
+ my @stats = stat($self->_root->{file});
+ $self->_root->{end} = $stats[7];
+
+ # double-check file inode, in case another process
+ # has optimize()d our file while we were waiting.
+ if ($stats[1] != $self->_root->{inode}) {
$self->{engine}->close_fh( $self );
$self->{engine}->setup_fh( $self );
- flock($self->_fh, $type); # re-lock
+ flock($self->_fh, $type); # re-lock
# This may not be necessary after re-opening
- $self->_root->{end} = (stat($self->_fh))[7]; # re-end
- }
- }
- $self->_root->{locked}++;
+ $self->_root->{end} = (stat($self->_fh))[7]; # re-end
+ }
+ }
+ $self->_root->{locked}++;
return 1;
- }
+ }
return;
}
sub unlock {
- ##
- # If db locking is set, unlock the db file. See note in lock()
- # regarding calling lock() multiple times.
- ##
+ ##
+ # If db locking is set, unlock the db file. See note in lock()
+ # regarding calling lock() multiple times.
+ ##
my $self = $_[0]->_get_self;
- if (!defined($self->_fh)) { return; }
-
- if ($self->_root->{locking} && $self->_root->{locked} > 0) {
- $self->_root->{locked}--;
- if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); }
+ if (!defined($self->_fh)) { return; }
+
+ if ($self->_root->{locking} && $self->_root->{locked} > 0) {
+ $self->_root->{locked}--;
+ if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); }
return 1;
- }
+ }
return;
}
}
sub _copy_node {
- ##
- # Copy single level of keys or elements to new DB handle.
- # Recurse for nested structures
- ##
+ ##
+ # Copy single level of keys or elements to new DB handle.
+ # Recurse for nested structures
+ ##
my $self = shift->_get_self;
- my ($db_temp) = @_;
+ my ($db_temp) = @_;
- if ($self->_type eq TYPE_HASH) {
- my $key = $self->first_key();
- while ($key) {
- my $value = $self->get($key);
+ if ($self->_type eq TYPE_HASH) {
+ my $key = $self->first_key();
+ while ($key) {
+ my $value = $self->get($key);
$self->_copy_value( \$db_temp->{$key}, $value );
- $key = $self->next_key($key);
- }
- }
- else {
- my $length = $self->length();
- for (my $index = 0; $index < $length; $index++) {
- my $value = $self->get($index);
+ $key = $self->next_key($key);
+ }
+ }
+ else {
+ my $length = $self->length();
+ for (my $index = 0; $index < $length; $index++) {
+ my $value = $self->get($index);
$self->_copy_value( \$db_temp->[$index], $value );
- }
- }
+ }
+ }
return 1;
}
sub export {
- ##
- # Recursively export into standard Perl hashes and arrays.
- ##
+ ##
+ # Recursively export into standard Perl hashes and arrays.
+ ##
my $self = $_[0]->_get_self;
-
- my $temp;
- if ($self->_type eq TYPE_HASH) { $temp = {}; }
- elsif ($self->_type eq TYPE_ARRAY) { $temp = []; }
-
- $self->lock();
- $self->_copy_node( $temp );
- $self->unlock();
-
- return $temp;
+
+ my $temp;
+ if ($self->_type eq TYPE_HASH) { $temp = {}; }
+ elsif ($self->_type eq TYPE_ARRAY) { $temp = []; }
+
+ $self->lock();
+ $self->_copy_node( $temp );
+ $self->unlock();
+
+ return $temp;
}
sub import {
- ##
- # Recursively import Perl hash/array structure
- ##
+ ##
+ # Recursively import Perl hash/array structure
+ ##
#XXX This use of ref() seems to be ok
- if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
-
+ if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
+
my $self = $_[0]->_get_self;
- my $struct = $_[1];
-
+ my $struct = $_[1];
+
#XXX This use of ref() seems to be ok
- if (!ref($struct)) {
- ##
- # struct is not a reference, so just import based on our type
- ##
- shift @_;
-
- if ($self->_type eq TYPE_HASH) { $struct = {@_}; }
- elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; }
- }
-
+ if (!ref($struct)) {
+ ##
+ # struct is not a reference, so just import based on our type
+ ##
+ shift @_;
+
+ if ($self->_type eq TYPE_HASH) { $struct = {@_}; }
+ elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; }
+ }
+
my $r = Scalar::Util::reftype($struct) || '';
- if ($r eq "HASH" && $self->_type eq TYPE_HASH) {
- foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
- }
- elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) {
- $self->push( @$struct );
- }
- else {
- return $self->_throw_error("Cannot import: type mismatch");
- }
-
- return 1;
+ if ($r eq "HASH" && $self->_type eq TYPE_HASH) {
+ foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
+ }
+ elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) {
+ $self->push( @$struct );
+ }
+ else {
+ return $self->_throw_error("Cannot import: type mismatch");
+ }
+
+ return 1;
}
sub optimize {
- ##
- # Rebuild entire database into new file, then move
- # it back on top of original.
- ##
+ ##
+ # Rebuild entire database into new file, then move
+ # it back on top of original.
+ ##
my $self = $_[0]->_get_self;
#XXX Need to create a new test for this
-# if ($self->_root->{links} > 1) {
-# return $self->_throw_error("Cannot optimize: reference count is greater than 1");
-# }
-
- my $db_temp = DBM::Deep->new(
- file => $self->_root->{file} . '.tmp',
- type => $self->_type
- );
- if (!$db_temp) {
- return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
- }
-
- $self->lock();
- $self->_copy_node( $db_temp );
- undef $db_temp;
-
- ##
- # Attempt to copy user, group and permissions over to new file
- ##
- my @stats = stat($self->_fh);
- my $perms = $stats[2] & 07777;
- my $uid = $stats[4];
- my $gid = $stats[5];
- chown( $uid, $gid, $self->_root->{file} . '.tmp' );
- chmod( $perms, $self->_root->{file} . '.tmp' );
-
+# if ($self->_root->{links} > 1) {
+# return $self->_throw_error("Cannot optimize: reference count is greater than 1");
+# }
+
+ my $db_temp = DBM::Deep->new(
+ file => $self->_root->{file} . '.tmp',
+ type => $self->_type
+ );
+ if (!$db_temp) {
+ return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
+ }
+
+ $self->lock();
+ $self->_copy_node( $db_temp );
+ undef $db_temp;
+
+ ##
+ # Attempt to copy user, group and permissions over to new file
+ ##
+ my @stats = stat($self->_fh);
+ my $perms = $stats[2] & 07777;
+ my $uid = $stats[4];
+ my $gid = $stats[5];
+ chown( $uid, $gid, $self->_root->{file} . '.tmp' );
+ chmod( $perms, $self->_root->{file} . '.tmp' );
+
# q.v. perlport for more information on this variable
if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) {
- ##
- # Potential race condition when optmizing on Win32 with locking.
- # The Windows filesystem requires that the filehandle be closed
- # before it is overwritten with rename(). This could be redone
- # with a soft copy.
- ##
- $self->unlock();
- $self->{engine}->close_fh( $self );
- }
-
- if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) {
- unlink $self->_root->{file} . '.tmp';
- $self->unlock();
- return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
- }
-
- $self->unlock();
- $self->{engine}->close_fh( $self );
+ ##
+ # Potential race condition when optmizing on Win32 with locking.
+ # The Windows filesystem requires that the filehandle be closed
+ # before it is overwritten with rename(). This could be redone
+ # with a soft copy.
+ ##
+ $self->unlock();
+ $self->{engine}->close_fh( $self );
+ }
+
+ if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) {
+ unlink $self->_root->{file} . '.tmp';
+ $self->unlock();
+ return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
+ }
+
+ $self->unlock();
+ $self->{engine}->close_fh( $self );
$self->{engine}->setup_fh( $self );
- return 1;
+ return 1;
}
sub clone {
- ##
- # Make copy of object and return
- ##
+ ##
+ # Make copy of object and return
+ ##
my $self = $_[0]->_get_self;
-
- return DBM::Deep->new(
- type => $self->_type,
- base_offset => $self->_base_offset,
- root => $self->_root
- );
+
+ return DBM::Deep->new(
+ type => $self->_type,
+ base_offset => $self->_base_offset,
+ root => $self->_root
+ );
}
{
my $self = $_[0]->_get_self;
my $type = lc $_[1];
my $func = $_[2] ? $_[2] : undef;
-
+
if ( $is_legal_filter{$type} ) {
$self->_root->{"filter_$type"} = $func;
return 1;
##
sub _root {
- ##
- # Get access to the root structure
- ##
+ ##
+ # Get access to the root structure
+ ##
my $self = $_[0]->_get_self;
- return $self->{root};
+ return $self->{root};
}
sub _fh {
- ##
- # Get access to the raw fh
- ##
+ ##
+ # Get access to the raw fh
+ ##
#XXX It will be useful, though, when we split out HASH and ARRAY
my $self = $_[0]->_get_self;
- return $self->_root->{fh};
+ return $self->_root->{fh};
}
sub _type {
- ##
- # Get type of current node (TYPE_HASH or TYPE_ARRAY)
- ##
+ ##
+ # Get type of current node (TYPE_HASH or TYPE_ARRAY)
+ ##
my $self = $_[0]->_get_self;
- return $self->{type};
+ return $self->{type};
}
sub _base_offset {
- ##
- # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
- ##
+ ##
+ # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
+ ##
my $self = $_[0]->_get_self;
- return $self->{base_offset};
+ return $self->{base_offset};
}
##
##
sub STORE {
- ##
- # Store single hash key/value or array element in database.
- ##
- my $self = $_[0]->_get_self;
- my $key = $_[1];
+ ##
+ # Store single hash key/value or array element in database.
+ ##
+ my $self = shift->_get_self;
+ my ($key, $value) = @_;
- # User may be storing a hash, in which case we do not want it run
- # through the filtering system
- my $value = ($self->_root->{filter_store_value} && !ref($_[2]))
- ? $self->_root->{filter_store_value}->($_[2])
- : $_[2];
-
- my $md5 = $self->{engine}{digest}->($key);
-
unless ( _is_writable( $self->_fh ) ) {
$self->_throw_error( 'Cannot write to a readonly filehandle' );
}
-
- ##
- # Request exclusive lock for writing
- ##
- $self->lock( LOCK_EX );
-
- my $fh = $self->_fh;
-
- ##
- # Locate offset for bucket list using digest index system
- ##
- my $tag = $self->{engine}->load_tag($self, $self->_base_offset);
- if (!$tag) {
- $tag = $self->{engine}->create_tag($self, $self->_base_offset, SIG_INDEX, chr(0) x $self->{engine}{index_size});
- }
-
- my $ch = 0;
- while ($tag->{signature} ne SIG_BLIST) {
- my $num = ord(substr($md5, $ch, 1));
-
- my $ref_loc = $tag->{offset} + ($num * $self->{engine}{long_size});
- my $new_tag = $self->{engine}->index_lookup($self, $tag, $num);
-
- if (!$new_tag) {
- seek($fh, $ref_loc + $self->_root->{file_offset}, SEEK_SET);
- print( $fh pack($self->{engine}{long_pack}, $self->_root->{end}) );
-
- $tag = $self->{engine}->create_tag(
- $self, $self->_root->{end},
- SIG_BLIST,
- chr(0) x $self->{engine}{bucket_list_size},
- );
-
- $tag->{ref_loc} = $ref_loc;
- $tag->{ch} = $ch;
-
- last;
- }
- else {
- $tag = $new_tag;
-
- $tag->{ref_loc} = $ref_loc;
- $tag->{ch} = $ch;
- }
- $ch++;
- }
-
- ##
- # Add key/value to bucket list
- ##
- my $result = $self->{engine}->add_bucket( $self, $tag, $md5, $key, $value );
-
- $self->unlock();
-
- return $result;
+
+ ##
+ # Request exclusive lock for writing
+ ##
+ $self->lock( LOCK_EX );
+
+ my $md5 = $self->{engine}{digest}->($key);
+
+ my $tag = $self->{engine}->find_bucket_list( $self, $md5, { create => 1 } );
+
+ # User may be storing a hash, in which case we do not want it run
+ # through the filtering system
+ if ( !ref($value) && $self->_root->{filter_store_value} ) {
+ $value = $self->_root->{filter_store_value}->( $value );
+ }
+
+ ##
+ # Add key/value to bucket list
+ ##
+ my $result = $self->{engine}->add_bucket( $self, $tag, $md5, $key, $value );
+
+ $self->unlock();
+
+ return $result;
}
sub FETCH {
- ##
- # Fetch single value or element given plain key or array index
- ##
+ ##
+ # Fetch single value or element given plain key or array index
+ ##
my $self = shift->_get_self;
my $key = shift;
- my $md5 = $self->{engine}{digest}->($key);
-
- ##
- # Request shared lock for reading
- ##
- $self->lock( LOCK_SH );
-
- my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
- if (!$tag) {
- $self->unlock();
- return;
- }
-
- ##
- # Get value from bucket list
- ##
- my $result = $self->{engine}->get_bucket_value( $self, $tag, $md5 );
-
- $self->unlock();
-
+ my $md5 = $self->{engine}{digest}->($key);
+
+ ##
+ # Request shared lock for reading
+ ##
+ $self->lock( LOCK_SH );
+
+ my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
+ if (!$tag) {
+ $self->unlock();
+ return;
+ }
+
+ ##
+ # Get value from bucket list
+ ##
+ my $result = $self->{engine}->get_bucket_value( $self, $tag, $md5 );
+
+ $self->unlock();
+
#XXX What is ref() checking here?
#YYY Filters only apply on scalar values, so the ref check is making
#YYY sure the fetched bucket is a scalar, not a child hash or array.
- return ($result && !ref($result) && $self->_root->{filter_fetch_value})
+ return ($result && !ref($result) && $self->_root->{filter_fetch_value})
? $self->_root->{filter_fetch_value}->($result)
: $result;
}
sub DELETE {
- ##
- # Delete single key/value pair or element given plain key or array index
- ##
+ ##
+ # Delete single key/value pair or element given plain key or array index
+ ##
my $self = $_[0]->_get_self;
- my $key = $_[1];
-
- my $md5 = $self->{engine}{digest}->($key);
-
- ##
- # Request exclusive lock for writing
- ##
- $self->lock( LOCK_EX );
-
- my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
- if (!$tag) {
- $self->unlock();
- return;
- }
-
- ##
- # Delete bucket
- ##
+ my $key = $_[1];
+
+ my $md5 = $self->{engine}{digest}->($key);
+
+ ##
+ # Request exclusive lock for writing
+ ##
+ $self->lock( LOCK_EX );
+
+ my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
+ if (!$tag) {
+ $self->unlock();
+ return;
+ }
+
+ ##
+ # Delete bucket
+ ##
my $value = $self->{engine}->get_bucket_value($self, $tag, $md5 );
- if ($value && !ref($value) && $self->_root->{filter_fetch_value}) {
+ if ($value && !ref($value) && $self->_root->{filter_fetch_value}) {
$value = $self->_root->{filter_fetch_value}->($value);
}
- my $result = $self->{engine}->delete_bucket( $self, $tag, $md5 );
-
- ##
- # If this object is an array and the key deleted was on the end of the stack,
- # decrement the length variable.
- ##
-
- $self->unlock();
-
- return $value;
+ my $result = $self->{engine}->delete_bucket( $self, $tag, $md5 );
+
+ ##
+ # If this object is an array and the key deleted was on the end of the stack,
+ # decrement the length variable.
+ ##
+
+ $self->unlock();
+
+ return $value;
}
sub EXISTS {
- ##
- # Check if a single key or element exists given plain key or array index
- ##
+ ##
+ # Check if a single key or element exists given plain key or array index
+ ##
my $self = $_[0]->_get_self;
- my $key = $_[1];
-
- my $md5 = $self->{engine}{digest}->($key);
-
- ##
- # Request shared lock for reading
- ##
- $self->lock( LOCK_SH );
-
- my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
-
- ##
- # For some reason, the built-in exists() function returns '' for false
- ##
- if (!$tag) {
- $self->unlock();
- return '';
- }
-
- ##
- # Check if bucket exists and return 1 or ''
- ##
- my $result = $self->{engine}->bucket_exists( $self, $tag, $md5 ) || '';
-
- $self->unlock();
-
- return $result;
+ my $key = $_[1];
+
+ my $md5 = $self->{engine}{digest}->($key);
+
+ ##
+ # Request shared lock for reading
+ ##
+ $self->lock( LOCK_SH );
+
+ my $tag = $self->{engine}->find_bucket_list( $self, $md5 );
+ if (!$tag) {
+ $self->unlock();
+
+ ##
+ # For some reason, the built-in exists() function returns '' for false
+ ##
+ return '';
+ }
+
+ ##
+ # Check if bucket exists and return 1 or ''
+ ##
+ my $result = $self->{engine}->bucket_exists( $self, $tag, $md5 ) || '';
+
+ $self->unlock();
+
+ return $result;
}
sub CLEAR {
- ##
- # Clear all keys from hash, or all elements from array.
- ##
+ ##
+ # Clear all keys from hash, or all elements from array.
+ ##
my $self = $_[0]->_get_self;
- ##
- # Request exclusive lock for writing
- ##
- $self->lock( LOCK_EX );
-
+ ##
+ # Request exclusive lock for writing
+ ##
+ $self->lock( LOCK_EX );
+
my $fh = $self->_fh;
- seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET);
- if (eof $fh) {
- $self->unlock();
- return;
- }
-
- $self->{engine}->create_tag($self, $self->_base_offset, $self->_type, chr(0) x $self->{engine}{index_size});
-
- $self->unlock();
-
- return 1;
+ seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET);
+ if (eof $fh) {
+ $self->unlock();
+ return;
+ }
+
+ $self->{engine}->create_tag($self, $self->_base_offset, $self->_type, chr(0) x $self->{engine}{index_size});
+
+ $self->unlock();
+
+ return 1;
}
##
use DBM::Deep;
my $db = DBM::Deep->new( "foo.db" );
-
+
$db->{key} = 'value'; # tie() style
print $db->{key};
-
+
$db->put('key' => 'value'); # OO style
print $db->get('key');
-
+
# true multi-level support
$db->{my_complex} = [
- 'hello', { perl => 'rules' },
- 42, 99,
+ 'hello', { perl => 'rules' },
+ 42, 99,
];
=head1 DESCRIPTION
-A unique flat-file database module, written in pure perl. True
-multi-level hash/array support (unlike MLDBM, which is faked), hybrid
-OO / tie() interface, cross-platform FTPable files, and quite fast. Can
-handle millions of keys and unlimited hash levels without significant
-slow-down. Written from the ground-up in pure perl -- this is NOT a
-wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
+A unique flat-file database module, written in pure perl. True
+multi-level hash/array support (unlike MLDBM, which is faked), hybrid
+OO / tie() interface, cross-platform FTPable files, and quite fast. Can
+handle millions of keys and unlimited hash levels without significant
+slow-down. Written from the ground-up in pure perl -- this is NOT a
+wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
Mac OS X and Windows.
=head1 INSTALLATION
Hopefully you are using Perl's excellent CPAN module, which will download
-and install the module for you. If not, get the tarball, and run these
+and install the module for you. If not, get the tarball, and run these
commands:
- tar zxf DBM-Deep-*
- cd DBM-Deep-*
- perl Makefile.PL
- make
- make test
- make install
+ tar zxf DBM-Deep-*
+ cd DBM-Deep-*
+ perl Makefile.PL
+ make
+ make test
+ make install
=head1 SETUP
-Construction can be done OO-style (which is the recommended way), or using
+Construction can be done OO-style (which is the recommended way), or using
Perl's tie() function. Both are examined here.
=head2 OO CONSTRUCTION
The recommended way to construct a DBM::Deep object is to use the new()
method, which gets you a blessed, tied hash or array reference.
- my $db = DBM::Deep->new( "foo.db" );
+ my $db = DBM::Deep->new( "foo.db" );
This opens a new database handle, mapped to the file "foo.db". If this
-file does not exist, it will automatically be created. DB files are
+file does not exist, it will automatically be created. DB files are
opened in "r+" (read/write) mode, and the type of object returned is a
hash, unless otherwise specified (see L<OPTIONS> below).
You can pass a number of options to the constructor to specify things like
locking, autoflush, etc. This is done by passing an inline hash:
- my $db = DBM::Deep->new(
- file => "foo.db",
- locking => 1,
- autoflush => 1
- );
+ my $db = DBM::Deep->new(
+ file => "foo.db",
+ locking => 1,
+ autoflush => 1
+ );
Notice that the filename is now specified I<inside> the hash with
-the "file" parameter, as opposed to being the sole argument to the
+the "file" parameter, as opposed to being the sole argument to the
constructor. This is required if any options are specified.
See L<OPTIONS> below for the complete list.
You can also start with an array instead of a hash. For this, you must
specify the C<type> parameter:
- my $db = DBM::Deep->new(
- file => "foo.db",
- type => DBM::Deep->TYPE_ARRAY
- );
+ my $db = DBM::Deep->new(
+ file => "foo.db",
+ type => DBM::Deep->TYPE_ARRAY
+ );
B<Note:> Specifing the C<type> parameter only takes effect when beginning
a new DB file. If you create a DBM::Deep object with an existing file, the
such as lock() and unlock(), but cannot be used to assign to the DBM::Deep
file (as expected with most tie'd objects).
- my %hash;
- my $db = tie %hash, "DBM::Deep", "foo.db";
-
- my @array;
- my $db = tie @array, "DBM::Deep", "bar.db";
+ my %hash;
+ my $db = tie %hash, "DBM::Deep", "foo.db";
+
+ my @array;
+ my $db = tie @array, "DBM::Deep", "bar.db";
As with the OO constructor, you can replace the DB filename parameter with
a hash containing one or more options (see L<OPTIONS> just below for the
complete list).
- tie %hash, "DBM::Deep", {
- file => "foo.db",
- locking => 1,
- autoflush => 1
- };
+ tie %hash, "DBM::Deep", {
+ file => "foo.db",
+ locking => 1,
+ autoflush => 1
+ };
=head2 OPTIONS
=item * file
Filename of the DB file to link the handle to. You can pass a full absolute
-filesystem path, partial path, or a plain filename if the file is in the
+filesystem path, partial path, or a plain filename if the file is in the
current working directory. This is a required parameter (though q.v. fh).
=item * fh
This parameter specifies what type of object to create, a hash or array. Use
one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
-This only takes effect when beginning a new file. This is an optional
+This only takes effect when beginning a new file. This is an optional
parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
=item * locking
Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
function to lock the database in exclusive mode for writes, and shared mode for
-reads. Pass any true value to enable. This affects the base DB handle I<and
-any child hashes or arrays> that use the same DB file. This is an optional
+reads. Pass any true value to enable. This affects the base DB handle I<and
+any child hashes or arrays> that use the same DB file. This is an optional
parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
=item * autoflush
-Specifies whether autoflush is to be enabled on the underlying filehandle.
-This obviously slows down write operations, but is required if you may have
-multiple processes accessing the same DB file (also consider enable I<locking>).
-Pass any true value to enable. This is an optional parameter, and defaults to 0
+Specifies whether autoflush is to be enabled on the underlying filehandle.
+This obviously slows down write operations, but is required if you may have
+multiple processes accessing the same DB file (also consider enable I<locking>).
+Pass any true value to enable. This is an optional parameter, and defaults to 0
(disabled).
=item * autobless
You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
or even nested hashes (or arrays) using standard Perl syntax:
- my $db = DBM::Deep->new( "foo.db" );
-
- $db->{mykey} = "myvalue";
- $db->{myhash} = {};
- $db->{myhash}->{subkey} = "subvalue";
+ my $db = DBM::Deep->new( "foo.db" );
+
+ $db->{mykey} = "myvalue";
+ $db->{myhash} = {};
+ $db->{myhash}->{subkey} = "subvalue";
- print $db->{myhash}->{subkey} . "\n";
+ print $db->{myhash}->{subkey} . "\n";
You can even step through hash keys using the normal Perl C<keys()> function:
- foreach my $key (keys %$db) {
- print "$key: " . $db->{$key} . "\n";
- }
+ foreach my $key (keys %$db) {
+ print "$key: " . $db->{$key} . "\n";
+ }
Remember that Perl's C<keys()> function extracts I<every> key from the hash and
-pushes them onto an array, all before the loop even begins. If you have an
-extra large hash, this may exhaust Perl's memory. Instead, consider using
-Perl's C<each()> function, which pulls keys/values one at a time, using very
+pushes them onto an array, all before the loop even begins. If you have an
+extra large hash, this may exhaust Perl's memory. Instead, consider using
+Perl's C<each()> function, which pulls keys/values one at a time, using very
little memory:
- while (my ($key, $value) = each %$db) {
- print "$key: $value\n";
- }
+ while (my ($key, $value) = each %$db) {
+ print "$key: $value\n";
+ }
Please note that when using C<each()>, you should always pass a direct
hash reference, not a lookup. Meaning, you should B<never> do this:
- # NEVER DO THIS
- while (my ($key, $value) = each %{$db->{foo}}) { # BAD
+ # NEVER DO THIS
+ while (my ($key, $value) = each %{$db->{foo}}) { # BAD
This causes an infinite loop, because for each iteration, Perl is calling
FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
-it effectively keeps returning the first key over and over again. Instead,
+it effectively keeps returning the first key over and over again. Instead,
assign a temporary variable to C<$db->{foo}>, then pass that to each().
=head2 ARRAYS
As with hashes, you can treat any DBM::Deep object like a normal Perl array
-reference. This includes inserting, removing and manipulating elements,
+reference. This includes inserting, removing and manipulating elements,
and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
-The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
+The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
or simply be a nested array reference inside a hash. Example:
- my $db = DBM::Deep->new(
- file => "foo-array.db",
- type => DBM::Deep->TYPE_ARRAY
- );
-
- $db->[0] = "foo";
- push @$db, "bar", "baz";
- unshift @$db, "bah";
-
- my $last_elem = pop @$db; # baz
- my $first_elem = shift @$db; # bah
- my $second_elem = $db->[1]; # bar
-
- my $num_elements = scalar @$db;
+ my $db = DBM::Deep->new(
+ file => "foo-array.db",
+ type => DBM::Deep->TYPE_ARRAY
+ );
+
+ $db->[0] = "foo";
+ push @$db, "bar", "baz";
+ unshift @$db, "bah";
+
+ my $last_elem = pop @$db; # baz
+ my $first_elem = shift @$db; # bah
+ my $second_elem = $db->[1]; # bar
+
+ my $num_elements = scalar @$db;
=head1 OO INTERFACE
In addition to the I<tie()> interface, you can also use a standard OO interface
to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
-array) has its own methods, but both types share the following common methods:
+array) has its own methods, but both types share the following common methods:
C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
=over
arguments, the hash key or array index, and the new value. The value can be
a scalar, hash ref or array ref. Returns true on success, false on failure.
- $db->put("foo", "bar"); # for hashes
- $db->put(1, "bar"); # for arrays
+ $db->put("foo", "bar"); # for hashes
+ $db->put(1, "bar"); # for arrays
=item * get() / fetch()
Fetches the value of a hash key or array element. Takes one argument: the hash
-key or array index. Returns a scalar, hash ref or array ref, depending on the
+key or array index. Returns a scalar, hash ref or array ref, depending on the
data type stored.
- my $value = $db->get("foo"); # for hashes
- my $value = $db->get(1); # for arrays
+ my $value = $db->get("foo"); # for hashes
+ my $value = $db->get(1); # for arrays
=item * exists()
-Checks if a hash key or array index exists. Takes one argument: the hash key
+Checks if a hash key or array index exists. Takes one argument: the hash key
or array index. Returns true if it exists, false if not.
- if ($db->exists("foo")) { print "yay!\n"; } # for hashes
- if ($db->exists(1)) { print "yay!\n"; } # for arrays
+ if ($db->exists("foo")) { print "yay!\n"; } # for hashes
+ if ($db->exists(1)) { print "yay!\n"; } # for arrays
=item * delete()
key or array index. Returns true on success, false if not found. For arrays,
the remaining elements located after the deleted element are NOT moved over.
The deleted element is essentially just undefined, which is exactly how Perl's
-internal arrays work. Please note that the space occupied by the deleted
-key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
+internal arrays work. Please note that the space occupied by the deleted
+key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
below for details and workarounds.
- $db->delete("foo"); # for hashes
- $db->delete(1); # for arrays
+ $db->delete("foo"); # for hashes
+ $db->delete(1); # for arrays
=item * clear()
-Deletes B<all> hash keys or array elements. Takes no arguments. No return
-value. Please note that the space occupied by the deleted keys/values or
-elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
+Deletes B<all> hash keys or array elements. Takes no arguments. No return
+value. Please note that the space occupied by the deleted keys/values or
+elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
details and workarounds.
- $db->clear(); # hashes or arrays
+ $db->clear(); # hashes or arrays
=item * lock() / unlock()
=head2 HASHES
-For hashes, DBM::Deep supports all the common methods described above, and the
+For hashes, DBM::Deep supports all the common methods described above, and the
following additional methods: C<first_key()> and C<next_key()>.
=over
=item * first_key()
-Returns the "first" key in the hash. As with built-in Perl hashes, keys are
-fetched in an undefined order (which appears random). Takes no arguments,
+Returns the "first" key in the hash. As with built-in Perl hashes, keys are
+fetched in an undefined order (which appears random). Takes no arguments,
returns the key as a scalar value.
- my $key = $db->first_key();
+ my $key = $db->first_key();
=item * next_key()
Returns the "next" key in the hash, given the previous one as the sole argument.
Returns undef if there are no more keys to be fetched.
- $key = $db->next_key($key);
+ $key = $db->next_key($key);
=back
Here are some examples of using hashes:
- my $db = DBM::Deep->new( "foo.db" );
-
- $db->put("foo", "bar");
- print "foo: " . $db->get("foo") . "\n";
-
- $db->put("baz", {}); # new child hash ref
- $db->get("baz")->put("buz", "biz");
- print "buz: " . $db->get("baz")->get("buz") . "\n";
-
- my $key = $db->first_key();
- while ($key) {
- print "$key: " . $db->get($key) . "\n";
- $key = $db->next_key($key);
- }
-
- if ($db->exists("foo")) { $db->delete("foo"); }
+ my $db = DBM::Deep->new( "foo.db" );
+
+ $db->put("foo", "bar");
+ print "foo: " . $db->get("foo") . "\n";
+
+ $db->put("baz", {}); # new child hash ref
+ $db->get("baz")->put("buz", "biz");
+ print "buz: " . $db->get("baz")->get("buz") . "\n";
+
+ my $key = $db->first_key();
+ while ($key) {
+ print "$key: " . $db->get($key) . "\n";
+ $key = $db->next_key($key);
+ }
+
+ if ($db->exists("foo")) { $db->delete("foo"); }
=head2 ARRAYS
-For arrays, DBM::Deep supports all the common methods described above, and the
-following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
+For arrays, DBM::Deep supports all the common methods described above, and the
+following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
C<unshift()> and C<splice()>.
=over
Returns the number of elements in the array. Takes no arguments.
- my $len = $db->length();
+ my $len = $db->length();
=item * push()
-Adds one or more elements onto the end of the array. Accepts scalars, hash
+Adds one or more elements onto the end of the array. Accepts scalars, hash
refs or array refs. No return value.
- $db->push("foo", "bar", {});
+ $db->push("foo", "bar", {});
=item * pop()
Fetches the last element in the array, and deletes it. Takes no arguments.
Returns undef if array is empty. Returns the element value.
- my $elem = $db->pop();
+ my $elem = $db->pop();
=item * shift()
-Fetches the first element in the array, deletes it, then shifts all the
-remaining elements over to take up the space. Returns the element value. This
-method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
+Fetches the first element in the array, deletes it, then shifts all the
+remaining elements over to take up the space. Returns the element value. This
+method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
details.
- my $elem = $db->shift();
+ my $elem = $db->shift();
=item * unshift()
-Inserts one or more elements onto the beginning of the array, shifting all
-existing elements over to make room. Accepts scalars, hash refs or array refs.
-No return value. This method is not recommended with large arrays -- see
+Inserts one or more elements onto the beginning of the array, shifting all
+existing elements over to make room. Accepts scalars, hash refs or array refs.
+No return value. This method is not recommended with large arrays -- see
<LARGE ARRAYS> below for details.
- $db->unshift("foo", "bar", {});
+ $db->unshift("foo", "bar", {});
=item * splice()
-Performs exactly like Perl's built-in function of the same name. See L<perldoc
+Performs exactly like Perl's built-in function of the same name. See L<perldoc
-f splice> for usage -- it is too complicated to document here. This method is
not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
Here are some examples of using arrays:
- my $db = DBM::Deep->new(
- file => "foo.db",
- type => DBM::Deep->TYPE_ARRAY
- );
-
- $db->push("bar", "baz");
- $db->unshift("foo");
- $db->put(3, "buz");
-
- my $len = $db->length();
- print "length: $len\n"; # 4
-
- for (my $k=0; $k<$len; $k++) {
- print "$k: " . $db->get($k) . "\n";
- }
-
- $db->splice(1, 2, "biz", "baf");
-
- while (my $elem = shift @$db) {
- print "shifted: $elem\n";
- }
+ my $db = DBM::Deep->new(
+ file => "foo.db",
+ type => DBM::Deep->TYPE_ARRAY
+ );
+
+ $db->push("bar", "baz");
+ $db->unshift("foo");
+ $db->put(3, "buz");
+
+ my $len = $db->length();
+ print "length: $len\n"; # 4
+
+ for (my $k=0; $k<$len; $k++) {
+ print "$k: " . $db->get($k) . "\n";
+ }
+
+ $db->splice(1, 2, "biz", "baf");
+
+ while (my $elem = shift @$db) {
+ print "shifted: $elem\n";
+ }
=head1 LOCKING
-Enable automatic file locking by passing a true value to the C<locking>
+Enable automatic file locking by passing a true value to the C<locking>
parameter when constructing your DBM::Deep object (see L<SETUP> above).
- my $db = DBM::Deep->new(
- file => "foo.db",
- locking => 1
- );
+ my $db = DBM::Deep->new(
+ file => "foo.db",
+ locking => 1
+ );
-This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
-mode for writes, and shared mode for reads. This is required if you have
-multiple processes accessing the same database file, to avoid file corruption.
-Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
+This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
+mode for writes, and shared mode for reads. This is required if you have
+multiple processes accessing the same database file, to avoid file corruption.
+Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
NFS> below for more.
=head2 EXPLICIT LOCKING
-You can explicitly lock a database, so it remains locked for multiple
-transactions. This is done by calling the C<lock()> method, and passing an
+You can explicitly lock a database, so it remains locked for multiple
+transactions. This is done by calling the C<lock()> method, and passing an
optional lock mode argument (defaults to exclusive mode). This is particularly
-useful for things like counters, where the current value needs to be fetched,
+useful for things like counters, where the current value needs to be fetched,
then incremented, then stored again.
- $db->lock();
- my $counter = $db->get("counter");
- $counter++;
- $db->put("counter", $counter);
- $db->unlock();
+ $db->lock();
+ my $counter = $db->get("counter");
+ $counter++;
+ $db->put("counter", $counter);
+ $db->unlock();
+
+ # or...
- # or...
-
- $db->lock();
- $db->{counter}++;
- $db->unlock();
+ $db->lock();
+ $db->{counter}++;
+ $db->unlock();
You can pass C<lock()> an optional argument, which specifies which mode to use
-(exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
-or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
+(exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
+or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
same as the constants defined in Perl's C<Fcntl> module.
- $db->lock( DBM::Deep->LOCK_SH );
- # something here
- $db->unlock();
+ $db->lock( DBM::Deep->LOCK_SH );
+ # something here
+ $db->unlock();
=head1 IMPORTING/EXPORTING
=head2 IMPORTING
Say you have an existing hash with nested hashes/arrays inside it. Instead of
-walking the structure and adding keys/elements to the database as you go,
-simply pass a reference to the C<import()> method. This recursively adds
+walking the structure and adding keys/elements to the database as you go,
+simply pass a reference to the C<import()> method. This recursively adds
everything to an existing DBM::Deep object for you. Here is an example:
- my $struct = {
- key1 => "value1",
- key2 => "value2",
- array1 => [ "elem0", "elem1", "elem2" ],
- hash1 => {
- subkey1 => "subvalue1",
- subkey2 => "subvalue2"
- }
- };
-
- my $db = DBM::Deep->new( "foo.db" );
- $db->import( $struct );
-
- print $db->{key1} . "\n"; # prints "value1"
-
-This recursively imports the entire C<$struct> object into C<$db>, including
+ my $struct = {
+ key1 => "value1",
+ key2 => "value2",
+ array1 => [ "elem0", "elem1", "elem2" ],
+ hash1 => {
+ subkey1 => "subvalue1",
+ subkey2 => "subvalue2"
+ }
+ };
+
+ my $db = DBM::Deep->new( "foo.db" );
+ $db->import( $struct );
+
+ print $db->{key1} . "\n"; # prints "value1"
+
+This recursively imports the entire C<$struct> object into C<$db>, including
all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
-keys are merged with the existing ones, replacing if they already exist.
-The C<import()> method can be called on any database level (not just the base
+keys are merged with the existing ones, replacing if they already exist.
+The C<import()> method can be called on any database level (not just the base
level), and works with both hash and array DB types.
B<Note:> Make sure your existing structure has no circular references in it.
=head2 EXPORTING
-Calling the C<export()> method on an existing DBM::Deep object will return
-a reference to a new in-memory copy of the database. The export is done
+Calling the C<export()> method on an existing DBM::Deep object will return
+a reference to a new in-memory copy of the database. The export is done
recursively, so all nested hashes/arrays are all exported to standard Perl
objects. Here is an example:
- my $db = DBM::Deep->new( "foo.db" );
-
- $db->{key1} = "value1";
- $db->{key2} = "value2";
- $db->{hash1} = {};
- $db->{hash1}->{subkey1} = "subvalue1";
- $db->{hash1}->{subkey2} = "subvalue2";
-
- my $struct = $db->export();
-
- print $struct->{key1} . "\n"; # prints "value1"
+ my $db = DBM::Deep->new( "foo.db" );
+
+ $db->{key1} = "value1";
+ $db->{key2} = "value2";
+ $db->{hash1} = {};
+ $db->{hash1}->{subkey1} = "subvalue1";
+ $db->{hash1}->{subkey2} = "subvalue2";
+
+ my $struct = $db->export();
+
+ print $struct->{key1} . "\n"; # prints "value1"
This makes a complete copy of the database in memory, and returns a reference
-to it. The C<export()> method can be called on any database level (not just
-the base level), and works with both hash and array DB types. Be careful of
-large databases -- you can store a lot more data in a DBM::Deep object than an
+to it. The C<export()> method can be called on any database level (not just
+the base level), and works with both hash and array DB types. Be careful of
+large databases -- you can store a lot more data in a DBM::Deep object than an
in-memory Perl structure.
B<Note:> Make sure your database has no circular references in it.
DBM::Deep has a number of hooks where you can specify your own Perl function
to perform filtering on incoming or outgoing data. This is a perfect
way to extend the engine, and implement things like real-time compression or
-encryption. Filtering applies to the base DB level, and all child hashes /
-arrays. Filter hooks can be specified when your DBM::Deep object is first
-constructed, or by calling the C<set_filter()> method at any time. There are
+encryption. Filtering applies to the base DB level, and all child hashes /
+arrays. Filter hooks can be specified when your DBM::Deep object is first
+constructed, or by calling the C<set_filter()> method at any time. There are
four available filter hooks, described below:
=over
=item * filter_store_key
-This filter is called whenever a hash key is stored. It
+This filter is called whenever a hash key is stored. It
is passed the incoming key, and expected to return a transformed key.
=item * filter_store_value
-This filter is called whenever a hash key or array element is stored. It
+This filter is called whenever a hash key or array element is stored. It
is passed the incoming value, and expected to return a transformed value.
=item * filter_fetch_key
-This filter is called whenever a hash key is fetched (i.e. via
+This filter is called whenever a hash key is fetched (i.e. via
C<first_key()> or C<next_key()>). It is passed the transformed key,
and expected to return the plain key.
=item * filter_fetch_value
-This filter is called whenever a hash key or array element is fetched.
+This filter is called whenever a hash key or array element is fetched.
It is passed the transformed value, and expected to return the plain value.
=back
Here are the two ways to setup a filter hook:
- my $db = DBM::Deep->new(
- file => "foo.db",
- filter_store_value => \&my_filter_store,
- filter_fetch_value => \&my_filter_fetch
- );
-
- # or...
-
- $db->set_filter( "filter_store_value", \&my_filter_store );
- $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
+ my $db = DBM::Deep->new(
+ file => "foo.db",
+ filter_store_value => \&my_filter_store,
+ filter_fetch_value => \&my_filter_fetch
+ );
+
+ # or...
+
+ $db->set_filter( "filter_store_value", \&my_filter_store );
+ $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
Your filter function will be called only when dealing with SCALAR keys or
values. When nested hashes and arrays are being stored/fetched, filtering
-is bypassed. Filters are called as static functions, passed a single SCALAR
+is bypassed. Filters are called as static functions, passed a single SCALAR
argument, and expected to return a single SCALAR value. If you want to
remove a filter, set the function reference to C<undef>:
- $db->set_filter( "filter_store_value", undef );
+ $db->set_filter( "filter_store_value", undef );
=head2 REAL-TIME ENCRYPTION EXAMPLE
-Here is a working example that uses the I<Crypt::Blowfish> module to
+Here is a working example that uses the I<Crypt::Blowfish> module to
do real-time encryption / decryption of keys & values with DBM::Deep Filters.
-Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
+Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
- use DBM::Deep;
- use Crypt::Blowfish;
- use Crypt::CBC;
-
- my $cipher = Crypt::CBC->new({
- 'key' => 'my secret key',
- 'cipher' => 'Blowfish',
- 'iv' => '$KJh#(}q',
- 'regenerate_key' => 0,
- 'padding' => 'space',
- 'prepend_iv' => 0
- });
-
- my $db = DBM::Deep->new(
- file => "foo-encrypt.db",
- filter_store_key => \&my_encrypt,
- filter_store_value => \&my_encrypt,
- filter_fetch_key => \&my_decrypt,
- filter_fetch_value => \&my_decrypt,
- );
-
- $db->{key1} = "value1";
- $db->{key2} = "value2";
- print "key1: " . $db->{key1} . "\n";
- print "key2: " . $db->{key2} . "\n";
-
- undef $db;
- exit;
-
- sub my_encrypt {
- return $cipher->encrypt( $_[0] );
- }
- sub my_decrypt {
- return $cipher->decrypt( $_[0] );
- }
+ use DBM::Deep;
+ use Crypt::Blowfish;
+ use Crypt::CBC;
+
+ my $cipher = Crypt::CBC->new({
+ 'key' => 'my secret key',
+ 'cipher' => 'Blowfish',
+ 'iv' => '$KJh#(}q',
+ 'regenerate_key' => 0,
+ 'padding' => 'space',
+ 'prepend_iv' => 0
+ });
+
+ my $db = DBM::Deep->new(
+ file => "foo-encrypt.db",
+ filter_store_key => \&my_encrypt,
+ filter_store_value => \&my_encrypt,
+ filter_fetch_key => \&my_decrypt,
+ filter_fetch_value => \&my_decrypt,
+ );
+
+ $db->{key1} = "value1";
+ $db->{key2} = "value2";
+ print "key1: " . $db->{key1} . "\n";
+ print "key2: " . $db->{key2} . "\n";
+
+ undef $db;
+ exit;
+
+ sub my_encrypt {
+ return $cipher->encrypt( $_[0] );
+ }
+ sub my_decrypt {
+ return $cipher->decrypt( $_[0] );
+ }
=head2 REAL-TIME COMPRESSION EXAMPLE
Here is a working example that uses the I<Compress::Zlib> module to do real-time
compression / decompression of keys & values with DBM::Deep Filters.
-Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
+Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
more on I<Compress::Zlib>.
- use DBM::Deep;
- use Compress::Zlib;
-
- my $db = DBM::Deep->new(
- file => "foo-compress.db",
- filter_store_key => \&my_compress,
- filter_store_value => \&my_compress,
- filter_fetch_key => \&my_decompress,
- filter_fetch_value => \&my_decompress,
- );
-
- $db->{key1} = "value1";
- $db->{key2} = "value2";
- print "key1: " . $db->{key1} . "\n";
- print "key2: " . $db->{key2} . "\n";
-
- undef $db;
- exit;
-
- sub my_compress {
- return Compress::Zlib::memGzip( $_[0] ) ;
- }
- sub my_decompress {
- return Compress::Zlib::memGunzip( $_[0] ) ;
- }
+ use DBM::Deep;
+ use Compress::Zlib;
+
+ my $db = DBM::Deep->new(
+ file => "foo-compress.db",
+ filter_store_key => \&my_compress,
+ filter_store_value => \&my_compress,
+ filter_fetch_key => \&my_decompress,
+ filter_fetch_value => \&my_decompress,
+ );
+
+ $db->{key1} = "value1";
+ $db->{key2} = "value2";
+ print "key1: " . $db->{key1} . "\n";
+ print "key2: " . $db->{key2} . "\n";
+
+ undef $db;
+ exit;
+
+ sub my_compress {
+ return Compress::Zlib::memGzip( $_[0] ) ;
+ }
+ sub my_decompress {
+ return Compress::Zlib::memGunzip( $_[0] ) ;
+ }
B<Note:> Filtering of keys only applies to hashes. Array "keys" are
actually numerical index numbers, and are not filtered.
Most DBM::Deep methods return a true value for success, and call die() on
failure. You can wrap calls in an eval block to catch the die.
- my $db = DBM::Deep->new( "foo.db" ); # create hash
- eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
-
+ my $db = DBM::Deep->new( "foo.db" ); # create hash
+ eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
+
print $@; # prints error message
=head1 LARGEFILE SUPPORT
DBM::Deep by default uses 32-bit file offset tags, but these can be changed
by calling the static C<set_pack()> method before you do anything else.
- DBM::Deep::set_pack(8, 'Q');
+ DBM::Deep::set_pack(8, 'Q');
-This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
-instead of 32-bit longs. After setting these values your DB files have a
+This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
+instead of 32-bit longs. After setting these values your DB files have a
theoretical maximum size of 16 XB (exabytes).
B<Note:> Changing these values will B<NOT> work for existing database files.
-Only change this for new files, and make sure it stays set consistently
-throughout the file's life. If you do set these values, you can no longer
-access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
+Only change this for new files, and make sure it stays set consistently
+throughout the file's life. If you do set these values, you can no longer
+access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
back to 32-bit mode.
-B<Note:> I have not personally tested files > 2 GB -- all my systems have
-only a 32-bit Perl. However, I have received user reports that this does
+B<Note:> I have not personally tested files > 2 GB -- all my systems have
+only a 32-bit Perl. However, I have received user reports that this does
indeed work!
=head1 LOW-LEVEL ACCESS
If you require low-level access to the underlying filehandle that DBM::Deep uses,
you can call the C<_fh()> method, which returns the handle:
- my $fh = $db->_fh();
+ my $fh = $db->_fh();
This method can be called on the root level of the datbase, or any child
hashes or arrays. All levels share a I<root> structure, which contains things
like the filehandle, a reference counter, and all the options specified
-when you created the object. You can get access to this root structure by
+when you created the object. You can get access to this root structure by
calling the C<root()> method.
- my $root = $db->_root();
+ my $root = $db->_root();
This is useful for changing options after the object has already been created,
such as enabling/disabling locking. You can also store your own temporary user
DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
keys. However you can override this, and use another algorithm (such as SHA-256)
-or even write your own. But please note that DBM::Deep currently expects zero
+or even write your own. But please note that DBM::Deep currently expects zero
collisions, so your algorithm has to be I<perfect>, so to speak.
Collision detection may be introduced in a later version.
-You can specify a custom digest algorithm by calling the static C<set_digest()>
-function, passing a reference to a subroutine, and the length of the algorithm's
-hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
-objects. Here is a working example that uses a 256-bit hash from the
-I<Digest::SHA256> module. Please see
+You can specify a custom digest algorithm by calling the static C<set_digest()>
+function, passing a reference to a subroutine, and the length of the algorithm's
+hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
+objects. Here is a working example that uses a 256-bit hash from the
+I<Digest::SHA256> module. Please see
L<http://search.cpan.org/search?module=Digest::SHA256> for more.
- use DBM::Deep;
- use Digest::SHA256;
-
- my $context = Digest::SHA256::new(256);
-
- DBM::Deep::set_digest( \&my_digest, 32 );
-
- my $db = DBM::Deep->new( "foo-sha.db" );
-
- $db->{key1} = "value1";
- $db->{key2} = "value2";
- print "key1: " . $db->{key1} . "\n";
- print "key2: " . $db->{key2} . "\n";
-
- undef $db;
- exit;
-
- sub my_digest {
- return substr( $context->hash($_[0]), 0, 32 );
- }
+ use DBM::Deep;
+ use Digest::SHA256;
+
+ my $context = Digest::SHA256::new(256);
+
+ DBM::Deep::set_digest( \&my_digest, 32 );
+
+ my $db = DBM::Deep->new( "foo-sha.db" );
+
+ $db->{key1} = "value1";
+ $db->{key2} = "value2";
+ print "key1: " . $db->{key1} . "\n";
+ print "key2: " . $db->{key2} . "\n";
+
+ undef $db;
+ exit;
+
+ sub my_digest {
+ return substr( $context->hash($_[0]), 0, 32 );
+ }
B<Note:> Your returned digest strings must be B<EXACTLY> the number
of bytes you specify in the C<set_digest()> function (in this case 32).
This relationship is stored in the DB file, and is preserved between sessions.
Here is an example:
- my $db = DBM::Deep->new( "foo.db" );
-
- $db->{foo} = "bar";
- $db->{circle} = $db; # ref to self
-
- print $db->{foo} . "\n"; # prints "foo"
- print $db->{circle}->{foo} . "\n"; # prints "foo" again
+ my $db = DBM::Deep->new( "foo.db" );
+
+ $db->{foo} = "bar";
+ $db->{circle} = $db; # ref to self
+
+ print $db->{foo} . "\n"; # prints "foo"
+ print $db->{circle}->{foo} . "\n"; # prints "foo" again
One catch is, passing the object to a function that recursively walks the
object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
-C<export()> methods) will result in an infinite loop. The other catch is,
-if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
-or C<next_key()> methods), you will get the I<target object's key>, not the
-ref's key. This gets even more interesting with the above example, where
-the I<circle> key points to the base DB object, which technically doesn't
-have a key. So I made DBM::Deep return "[base]" as the key name in that
+C<export()> methods) will result in an infinite loop. The other catch is,
+if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
+or C<next_key()> methods), you will get the I<target object's key>, not the
+ref's key. This gets even more interesting with the above example, where
+the I<circle> key points to the base DB object, which technically doesn't
+have a key. So I made DBM::Deep return "[base]" as the key name in that
special case.
=head1 CAVEATS / ISSUES / BUGS
One major caveat with DBM::Deep is that space occupied by existing keys and
values is not recovered when they are deleted. Meaning if you keep deleting
and adding new keys, your file will continuously grow. I am working on this,
-but in the meantime you can call the built-in C<optimize()> method from time to
+but in the meantime you can call the built-in C<optimize()> method from time to
time (perhaps in a crontab or something) to recover all your unused space.
- $db->optimize(); # returns true on success
+ $db->optimize(); # returns true on success
This rebuilds the ENTIRE database into a new file, then moves it on top of
the original. The new file will have no unused space, thus it will take up as
-little disk space as possible. Please note that this operation can take
-a long time for large files, and you need enough disk space to temporarily hold
-2 copies of your DB file. The temporary file is created in the same directory
-as the original, named with a ".tmp" extension, and is deleted when the
-operation completes. Oh, and if locking is enabled, the DB is automatically
+little disk space as possible. Please note that this operation can take
+a long time for large files, and you need enough disk space to temporarily hold
+2 copies of your DB file. The temporary file is created in the same directory
+as the original, named with a ".tmp" extension, and is deleted when the
+operation completes. Oh, and if locking is enabled, the DB is automatically
locked for the entire duration of the copy.
-B<WARNING:> Only call optimize() on the top-level node of the database, and
-make sure there are no child references lying around. DBM::Deep keeps a reference
+B<WARNING:> Only call optimize() on the top-level node of the database, and
+make sure there are no child references lying around. DBM::Deep keeps a reference
counter, and if it is greater than 1, optimize() will abort and return undef.
=head2 AUTOVIVIFICATION
-Unfortunately, autovivification doesn't work with tied hashes. This appears to
-be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
+Unfortunately, autovivification doesn't work with tied hashes. This appears to
+be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
-and it is also mentioned in the BUGS section for the I<MLDBM> module <see
+and it is also mentioned in the BUGS section for the I<MLDBM> module <see
L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
this does not work:
- $db->{foo}->{bar} = "hello";
+ $db->{foo}->{bar} = "hello";
Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
being an empty hash. Try this instead, which works fine:
- $db->{foo} = { bar => "hello" };
+ $db->{foo} = { bar => "hello" };
As of Perl 5.8.7, this bug still exists. I have walked very carefully through
the execution path, and Perl indeed passes an empty hash to the STORE() method.
segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
stuck in an infinite loop depending on the level of corruption. File write
operations are not checked for failure (for speed), so if you happen to run
-out of disk space, DBM::Deep will probably fail in a bad way. These things will
+out of disk space, DBM::Deep will probably fail in a bad way. These things will
be addressed in a later version of DBM::Deep.
=head2 DB OVER NFS
Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
-filesystems, but will NOT protect you from file corruption over NFS. I've heard
-about setting up your NFS server with a locking daemon, then using lockf() to
-lock your files, but your mileage may vary there as well. From what I
-understand, there is no real way to do it. However, if you need access to the
-underlying filehandle in DBM::Deep for using some other kind of locking scheme like
+filesystems, but will NOT protect you from file corruption over NFS. I've heard
+about setting up your NFS server with a locking daemon, then using lockf() to
+lock your files, but your mileage may vary there as well. From what I
+understand, there is no real way to do it. However, if you need access to the
+underlying filehandle in DBM::Deep for using some other kind of locking scheme like
lockf(), see the L<LOW-LEVEL ACCESS> section above.
=head2 COPYING OBJECTS
-Beware of copying tied objects in Perl. Very strange things can happen.
-Instead, use DBM::Deep's C<clone()> method which safely copies the object and
+Beware of copying tied objects in Perl. Very strange things can happen.
+Instead, use DBM::Deep's C<clone()> method which safely copies the object and
returns a new, blessed, tied hash or array to the same level in the DB.
- my $copy = $db->clone();
+ my $copy = $db->clone();
B<Note>: Since clone() here is cloning the object, not the database location, any
modifications to either $db or $copy will be visible in both.
=head2 SPEED
-Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
+Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
the almighty I<BerkeleyDB>. But it makes up for it in features like true
multi-level hash/array support, and cross-platform FTPable files. Even so,
DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
with huge databases. Here is some test data:
-
- Adding 1,000,000 keys to new DB file...
-
- At 100 keys, avg. speed is 2,703 keys/sec
- At 200 keys, avg. speed is 2,642 keys/sec
- At 300 keys, avg. speed is 2,598 keys/sec
- At 400 keys, avg. speed is 2,578 keys/sec
- At 500 keys, avg. speed is 2,722 keys/sec
- At 600 keys, avg. speed is 2,628 keys/sec
- At 700 keys, avg. speed is 2,700 keys/sec
- At 800 keys, avg. speed is 2,607 keys/sec
- At 900 keys, avg. speed is 2,190 keys/sec
- At 1,000 keys, avg. speed is 2,570 keys/sec
- At 2,000 keys, avg. speed is 2,417 keys/sec
- At 3,000 keys, avg. speed is 1,982 keys/sec
- At 4,000 keys, avg. speed is 1,568 keys/sec
- At 5,000 keys, avg. speed is 1,533 keys/sec
- At 6,000 keys, avg. speed is 1,787 keys/sec
- At 7,000 keys, avg. speed is 1,977 keys/sec
- At 8,000 keys, avg. speed is 2,028 keys/sec
- At 9,000 keys, avg. speed is 2,077 keys/sec
- At 10,000 keys, avg. speed is 2,031 keys/sec
- At 20,000 keys, avg. speed is 1,970 keys/sec
- At 30,000 keys, avg. speed is 2,050 keys/sec
- At 40,000 keys, avg. speed is 2,073 keys/sec
- At 50,000 keys, avg. speed is 1,973 keys/sec
- At 60,000 keys, avg. speed is 1,914 keys/sec
- At 70,000 keys, avg. speed is 2,091 keys/sec
- At 80,000 keys, avg. speed is 2,103 keys/sec
- At 90,000 keys, avg. speed is 1,886 keys/sec
- At 100,000 keys, avg. speed is 1,970 keys/sec
- At 200,000 keys, avg. speed is 2,053 keys/sec
- At 300,000 keys, avg. speed is 1,697 keys/sec
- At 400,000 keys, avg. speed is 1,838 keys/sec
- At 500,000 keys, avg. speed is 1,941 keys/sec
- At 600,000 keys, avg. speed is 1,930 keys/sec
- At 700,000 keys, avg. speed is 1,735 keys/sec
- At 800,000 keys, avg. speed is 1,795 keys/sec
- At 900,000 keys, avg. speed is 1,221 keys/sec
- At 1,000,000 keys, avg. speed is 1,077 keys/sec
-
-This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
-5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
-values were between 6 - 12 chars in length. The DB file ended up at 210MB.
+
+ Adding 1,000,000 keys to new DB file...
+
+ At 100 keys, avg. speed is 2,703 keys/sec
+ At 200 keys, avg. speed is 2,642 keys/sec
+ At 300 keys, avg. speed is 2,598 keys/sec
+ At 400 keys, avg. speed is 2,578 keys/sec
+ At 500 keys, avg. speed is 2,722 keys/sec
+ At 600 keys, avg. speed is 2,628 keys/sec
+ At 700 keys, avg. speed is 2,700 keys/sec
+ At 800 keys, avg. speed is 2,607 keys/sec
+ At 900 keys, avg. speed is 2,190 keys/sec
+ At 1,000 keys, avg. speed is 2,570 keys/sec
+ At 2,000 keys, avg. speed is 2,417 keys/sec
+ At 3,000 keys, avg. speed is 1,982 keys/sec
+ At 4,000 keys, avg. speed is 1,568 keys/sec
+ At 5,000 keys, avg. speed is 1,533 keys/sec
+ At 6,000 keys, avg. speed is 1,787 keys/sec
+ At 7,000 keys, avg. speed is 1,977 keys/sec
+ At 8,000 keys, avg. speed is 2,028 keys/sec
+ At 9,000 keys, avg. speed is 2,077 keys/sec
+ At 10,000 keys, avg. speed is 2,031 keys/sec
+ At 20,000 keys, avg. speed is 1,970 keys/sec
+ At 30,000 keys, avg. speed is 2,050 keys/sec
+ At 40,000 keys, avg. speed is 2,073 keys/sec
+ At 50,000 keys, avg. speed is 1,973 keys/sec
+ At 60,000 keys, avg. speed is 1,914 keys/sec
+ At 70,000 keys, avg. speed is 2,091 keys/sec
+ At 80,000 keys, avg. speed is 2,103 keys/sec
+ At 90,000 keys, avg. speed is 1,886 keys/sec
+ At 100,000 keys, avg. speed is 1,970 keys/sec
+ At 200,000 keys, avg. speed is 2,053 keys/sec
+ At 300,000 keys, avg. speed is 1,697 keys/sec
+ At 400,000 keys, avg. speed is 1,838 keys/sec
+ At 500,000 keys, avg. speed is 1,941 keys/sec
+ At 600,000 keys, avg. speed is 1,930 keys/sec
+ At 700,000 keys, avg. speed is 1,735 keys/sec
+ At 800,000 keys, avg. speed is 1,795 keys/sec
+ At 900,000 keys, avg. speed is 1,221 keys/sec
+ At 1,000,000 keys, avg. speed is 1,077 keys/sec
+
+This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
+5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
+values were between 6 - 12 chars in length. The DB file ended up at 210MB.
Run time was 12 min 3 sec.
=head2 MEMORY USAGE
and fetching data. Here is output from I</usr/bin/top> before even opening a
database handle:
- PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
- 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
+ PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
+ 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
-Basically the process is taking 2,716K of memory. And here is the same
+Basically the process is taking 2,716K of memory. And here is the same
process after storing and fetching 1,000,000 keys:
- PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
- 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
+ PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
+ 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
-Notice the memory usage increased by only 56K. Test was performed on a 700mHz
+Notice the memory usage increased by only 56K. Test was performed on a 700mHz
x86 box running Linux RedHat 7.2 & Perl 5.6.1.
=head1 DB FILE FORMAT
In case you were interested in the underlying DB file format, it is documented
-here in this section. You don't need to know this to use the module, it's just
+here in this section. You don't need to know this to use the module, it's just
included for reference.
=head2 SIGNATURE
=head2 TAG
The DBM::Deep file is in a I<tagged format>, meaning each section of the file
-has a standard header containing the type of data, the length of data, and then
-the data itself. The type is a single character (1 byte), the length is a
+has a standard header containing the type of data, the length of data, and then
+the data itself. The type is a single character (1 byte), the length is a
32-bit unsigned long in network byte order, and the data is, well, the data.
Here is how it unfolds:
=head2 MASTER INDEX
-Immediately after the 32-bit file signature is the I<Master Index> record.
-This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
-bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
+Immediately after the 32-bit file signature is the I<Master Index> record.
+This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
+bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
depending on how the DBM::Deep object was constructed.
-The index works by looking at a I<MD5 Hash> of the hash key (or array index
-number). The first 8-bit char of the MD5 signature is the offset into the
-index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
+The index works by looking at a I<MD5 Hash> of the hash key (or array index
+number). The first 8-bit char of the MD5 signature is the offset into the
+index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
index element is a file offset of the next tag for the key/element in question,
which is usually a I<Bucket List> tag (see below).
=head2 BUCKET LIST
-A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
-file offsets to where the actual data is stored. It starts with a standard
-tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
+A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
+file offsets to where the actual data is stored. It starts with a standard
+tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
-When the list fills up, a I<Re-Index> operation is performed (See
+When the list fills up, a I<Re-Index> operation is performed (See
L<RE-INDEXING> below).
=head2 BUCKET
type I<D> for scalar data (string, binary, etc.), or it could be a nested
hash (type I<H>) or array (type I<A>). The value comes just after the tag
header. The size reported in the tag header is only for the value, but then,
-just after the value is another size (32-bit unsigned long) and then the plain
-key itself. Since the value is likely to be fetched more often than the plain
+just after the value is another size (32-bit unsigned long) and then the plain
+key itself. Since the value is likely to be fetched more often than the plain
key, I figured it would be I<slightly> faster to store the value first.
If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
=head2 RE-INDEXING
After a I<Bucket List> grows to 16 records, its allocated space in the file is
-exhausted. Then, when another key/element comes in, the list is converted to a
-new index record. However, this index will look at the next char in the MD5
-hash, and arrange new Bucket List pointers accordingly. This process is called
-I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
-17 (16 + new one) keys/elements are removed from the old Bucket List and
-inserted into the new index. Several new Bucket Lists are created in the
-process, as a new MD5 char from the key is being examined (it is unlikely that
+exhausted. Then, when another key/element comes in, the list is converted to a
+new index record. However, this index will look at the next char in the MD5
+hash, and arrange new Bucket List pointers accordingly. This process is called
+I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
+17 (16 + new one) keys/elements are removed from the old Bucket List and
+inserted into the new index. Several new Bucket Lists are created in the
+process, as a new MD5 char from the key is being examined (it is unlikely that
the keys will all share the same next char of their MD5s).
Because of the way the I<MD5> algorithm works, it is impossible to tell exactly
-when the Bucket Lists will turn into indexes, but the first round tends to
-happen right around 4,000 keys. You will see a I<slight> decrease in
-performance here, but it picks back up pretty quick (see L<SPEED> above). Then
-it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
-right around 900,000 keys. This process can continue nearly indefinitely --
-right up until the point the I<MD5> signatures start colliding with each other,
-and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
-getting struck by lightning while you are walking to cash in your tickets.
-Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
-340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
+when the Bucket Lists will turn into indexes, but the first round tends to
+happen right around 4,000 keys. You will see a I<slight> decrease in
+performance here, but it picks back up pretty quick (see L<SPEED> above). Then
+it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
+right around 900,000 keys. This process can continue nearly indefinitely --
+right up until the point the I<MD5> signatures start colliding with each other,
+and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
+getting struck by lightning while you are walking to cash in your tickets.
+Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
+340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
this is 340 unodecillion, but don't quote me).
=head2 STORING
-When a new key/element is stored, the key (or index number) is first run through
-I<Digest::MD5> to get a 128-bit signature (example, in hex:
+When a new key/element is stored, the key (or index number) is first run through
+I<Digest::MD5> to get a 128-bit signature (example, in hex:
b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked
for the first char of the signature (in this case I<b0>). If it does not exist,
-a new I<Bucket List> is created for our key (and the next 15 future keys that
-happen to also have I<b> as their first MD5 char). The entire MD5 is written
+a new I<Bucket List> is created for our key (and the next 15 future keys that
+happen to also have I<b> as their first MD5 char). The entire MD5 is written
to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at
-this point, unless we are replacing an existing I<Bucket>), where the actual
+this point, unless we are replacing an existing I<Bucket>), where the actual
data will be stored.
=head2 FETCHING
-Fetching an existing key/element involves getting a I<Digest::MD5> of the key
-(or index number), then walking along the indexes. If there are enough
-keys/elements in this DB level, there might be nested indexes, each linked to
-a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
-contains up to 16 full MD5 hashes. Each is checked for equality to the key in
-question. If we found a match, the I<Bucket> tag is loaded, where the value and
+Fetching an existing key/element involves getting a I<Digest::MD5> of the key
+(or index number), then walking along the indexes. If there are enough
+keys/elements in this DB level, there might be nested indexes, each linked to
+a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
+contains up to 16 full MD5 hashes. Each is checked for equality to the key in
+question. If we found a match, the I<Bucket> tag is loaded, where the value and
plain key are stored.
Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
methods. In this process the indexes are walked systematically, and each key
fetched in increasing MD5 order (which is why it appears random). Once the
-I<Bucket> is found, the value is skipped and the plain key returned instead.
-B<Note:> Do not count on keys being fetched as if the MD5 hashes were
-alphabetically sorted. This only happens on an index-level -- as soon as the
-I<Bucket Lists> are hit, the keys will come out in the order they went in --
-so it's pretty much undefined how the keys will come out -- just like Perl's
+I<Bucket> is found, the value is skipped and the plain key returned instead.
+B<Note:> Do not count on keys being fetched as if the MD5 hashes were
+alphabetically sorted. This only happens on an index-level -- as soon as the
+I<Bucket Lists> are hit, the keys will come out in the order they went in --
+so it's pretty much undefined how the keys will come out -- just like Perl's
built-in hashes.
=head1 CODE COVERAGE
projects / dbsrgits/DBM-Deep.git / commitdiff