use strict;
use warnings FATAL => 'all';
-# Never import symbols into our namespace. We are a class, not a library.
-# -RobK, 2008-05-27
-use Scalar::Util ();
+our $VERSION = $DBM::Deep::VERSION;
-#use Data::Dumper ();
+use DBM::Deep::Iterator ();
# File-wide notes:
# * Every method in here assumes that the storage has been appropriately
# mutex. But, it's the caller's responsability to make sure that this has
# been done.
-# Setup file and tag signatures. These should never change.
-sub SIG_FILE () { 'DPDB' }
-sub SIG_HEADER () { 'h' }
-sub SIG_HASH () { 'H' }
-sub SIG_ARRAY () { 'A' }
-sub SIG_NULL () { 'N' }
-sub SIG_DATA () { 'D' }
-sub SIG_INDEX () { 'I' }
-sub SIG_BLIST () { 'B' }
-sub SIG_FREE () { 'F' }
-sub SIG_SIZE () { 1 }
-
-our $STALE_SIZE = 2;
-
-# Please refer to the pack() documentation for further information
-my %StP = (
- 1 => 'C', # Unsigned char value (no order needed as it's just one byte)
- 2 => 'n', # Unsigned short in "network" (big-endian) order
- 4 => 'N', # Unsigned long in "network" (big-endian) order
- 8 => 'Q', # Usigned quad (no order specified, presumably machine-dependent)
-);
-sub StP { $StP{$_[1]} }
-
-# Import these after the SIG_* definitions because those definitions are used
-# in the headers of these classes. -RobK, 2008-06-20
-use DBM::Deep::Engine::Sector::BucketList;
-use DBM::Deep::Engine::Sector::FileHeader;
-use DBM::Deep::Engine::Sector::Index;
-use DBM::Deep::Engine::Sector::Null;
-use DBM::Deep::Engine::Sector::Reference;
-use DBM::Deep::Engine::Sector::Scalar;
-use DBM::Deep::Iterator;
-
-################################################################################
-
-sub new {
- my $class = shift;
- my ($args) = @_;
-
- $args->{storage} = DBM::Deep::File->new( $args )
- unless exists $args->{storage};
-
- my $self = bless {
- byte_size => 4,
-
- digest => undef,
- hash_size => 16, # In bytes
- hash_chars => 256, # Number of chars the algorithm uses per byte
- max_buckets => 16,
- num_txns => 1, # The HEAD
- trans_id => 0, # Default to the HEAD
-
- data_sector_size => 64, # Size in bytes of each data sector
-
- entries => {}, # This is the list of entries for transactions
- storage => undef,
- }, $class;
-
- # Never allow byte_size to be set directly.
- delete $args->{byte_size};
- if ( defined $args->{pack_size} ) {
- if ( lc $args->{pack_size} eq 'small' ) {
- $args->{byte_size} = 2;
- }
- elsif ( lc $args->{pack_size} eq 'medium' ) {
- $args->{byte_size} = 4;
- }
- elsif ( lc $args->{pack_size} eq 'large' ) {
- $args->{byte_size} = 8;
- }
- else {
- DBM::Deep->_throw_error( "Unknown pack_size value: '$args->{pack_size}'" );
- }
- }
+sub SIG_HASH () { 'H' }
+sub SIG_ARRAY () { 'A' }
- # Grab the parameters we want to use
- foreach my $param ( keys %$self ) {
- next unless exists $args->{$param};
- $self->{$param} = $args->{$param};
- }
+=head1 NAME
- my %validations = (
- max_buckets => { floor => 16, ceil => 256 },
- num_txns => { floor => 1, ceil => 255 },
- data_sector_size => { floor => 32, ceil => 256 },
- );
-
- while ( my ($attr, $c) = each %validations ) {
- if ( !defined $self->{$attr}
- || !length $self->{$attr}
- || $self->{$attr} =~ /\D/
- || $self->{$attr} < $c->{floor}
- ) {
- $self->{$attr} = '(undef)' if !defined $self->{$attr};
- warn "Floor of $attr is $c->{floor}. Setting it to $c->{floor} from '$self->{$attr}'\n";
- $self->{$attr} = $c->{floor};
- }
- elsif ( $self->{$attr} > $c->{ceil} ) {
- warn "Ceiling of $attr is $c->{ceil}. Setting it to $c->{ceil} from '$self->{$attr}'\n";
- $self->{$attr} = $c->{ceil};
- }
- }
+DBM::Deep::Engine
- if ( !$self->{digest} ) {
- require Digest::MD5;
- $self->{digest} = \&Digest::MD5::md5;
- }
+=head1 PURPOSE
- return $self;
-}
+This is an internal-use-only object for L<DBM::Deep>. It mediates the low-level
+mapping between the L<DBM::Deep> objects and the storage medium.
-################################################################################
+The purpose of this documentation is to provide low-level documentation for
+developers. It is B<not> intended to be used by the general public. This
+documentation and what it documents can and will change without notice.
-sub read_value {
- my $self = shift;
- my ($obj, $key) = @_;
+=head1 OVERVIEW
- # This will be a Reference sector
- my $sector = $self->_load_sector( $obj->_base_offset )
- or return;
+The engine exposes an API to the DBM::Deep objects (DBM::Deep, DBM::Deep::Array,
+and DBM::Deep::Hash) for their use to access the actual stored values. This API
+is the following:
- if ( $sector->staleness != $obj->_staleness ) {
- return;
- }
+=over 4
- my $key_md5 = $self->_apply_digest( $key );
+=item * new
- my $value_sector = $sector->get_data_for({
- key_md5 => $key_md5,
- allow_head => 1,
- });
+=item * read_value
- unless ( $value_sector ) {
- $value_sector = DBM::Deep::Engine::Sector::Null->new({
- engine => $self,
- data => undef,
- });
+=item * get_classname
- $sector->write_data({
- key_md5 => $key_md5,
- key => $key,
- value => $value_sector,
- });
- }
+=item * make_reference
- return $value_sector->data;
-}
+=item * key_exists
-sub get_classname {
- my $self = shift;
- my ($obj) = @_;
+=item * delete_key
- # This will be a Reference sector
- my $sector = $self->_load_sector( $obj->_base_offset )
- or DBM::Deep->_throw_error( "How did get_classname fail (no sector for '$obj')?!" );
+=item * write_value
- if ( $sector->staleness != $obj->_staleness ) {
- return;
- }
+=item * get_next_key
- return $sector->get_classname;
-}
+=item * setup
-sub make_reference {
- my $self = shift;
- my ($obj, $old_key, $new_key) = @_;
+=item * begin_work
- # This will be a Reference sector
- my $sector = $self->_load_sector( $obj->_base_offset )
- or DBM::Deep->_throw_error( "How did make_reference fail (no sector for '$obj')?!" );
+=item * commit
- if ( $sector->staleness != $obj->_staleness ) {
- return;
- }
+=item * rollback
- my $old_md5 = $self->_apply_digest( $old_key );
+=item * lock_exclusive
- my $value_sector = $sector->get_data_for({
- key_md5 => $old_md5,
- allow_head => 1,
- });
+=item * lock_shared
- unless ( $value_sector ) {
- $value_sector = DBM::Deep::Engine::Sector::Null->new({
- engine => $self,
- data => undef,
- });
+=item * unlock
- $sector->write_data({
- key_md5 => $old_md5,
- key => $old_key,
- value => $value_sector,
- });
- }
+=back
- if ( $value_sector->isa( 'DBM::Deep::Engine::Sector::Reference' ) ) {
- $sector->write_data({
- key => $new_key,
- key_md5 => $self->_apply_digest( $new_key ),
- value => $value_sector,
- });
- $value_sector->increment_refcount;
- }
- else {
- $sector->write_data({
- key => $new_key,
- key_md5 => $self->_apply_digest( $new_key ),
- value => $value_sector->clone,
- });
- }
-}
+They are explained in their own sections below. These methods, in turn, may
+provide some bounds-checking, but primarily act to instantiate objects in the
+Engine::Sector::* hierarchy and dispatch to them.
-sub key_exists {
- my $self = shift;
- my ($obj, $key) = @_;
+=head1 TRANSACTIONS
- # This will be a Reference sector
- my $sector = $self->_load_sector( $obj->_base_offset )
- or return '';
+Transactions in DBM::Deep are implemented using a variant of MVCC. This attempts
+to keep the amount of actual work done against the file low while stil providing
+Atomicity, Consistency, and Isolation. Durability, unfortunately, cannot be done
+with only one file.
- if ( $sector->staleness != $obj->_staleness ) {
- return '';
- }
+=head2 STALENESS
- my $data = $sector->get_data_for({
- key_md5 => $self->_apply_digest( $key ),
- allow_head => 1,
- });
+If another process uses a transaction slot and writes stuff to it, then
+terminates, the data that process wrote it still within the file. In order to
+address this, there is also a transaction staleness counter associated within
+every write. Each time a transaction is started, that process increments that
+transaction's staleness counter. If, when it reads a value, the staleness
+counters aren't identical, DBM::Deep will consider the value on disk to be stale
+and discard it.
- # exists() returns 1 or '' for true/false.
- return $data ? 1 : '';
-}
+=head2 DURABILITY
-sub delete_key {
- my $self = shift;
- my ($obj, $key) = @_;
+The fourth leg of ACID is Durability, the guarantee that when a commit returns,
+the data will be there the next time you read from it. This should be regardless
+of any crashes or powerdowns in between the commit and subsequent read.
+DBM::Deep does provide that guarantee; once the commit returns, all of the data
+has been transferred from the transaction shadow to the HEAD. The issue arises
+with partial commits - a commit that is interrupted in some fashion. In keeping
+with DBM::Deep's "tradition" of very light error-checking and non-existent
+error-handling, there is no way to recover from a partial commit. (This is
+probably a failure in Consistency as well as Durability.)
- my $sector = $self->_load_sector( $obj->_base_offset )
- or return;
+Other DBMSes use transaction logs (a separate file, generally) to achieve
+Durability. As DBM::Deep is a single-file, we would have to do something
+similar to what SQLite and BDB do in terms of committing using synchonized
+writes. To do this, we would have to use a much higher RAM footprint and some
+serious programming that make my head hurts just to think about it.
- if ( $sector->staleness != $obj->_staleness ) {
- return;
- }
+=cut
- return $sector->delete_key({
- key_md5 => $self->_apply_digest( $key ),
- allow_head => 0,
- });
-}
+=head2 read_value( $obj, $key )
-sub write_value {
- my $self = shift;
- my ($obj, $key, $value) = @_;
+This takes an object that provides _base_offset() and a string. It returns the
+value stored in the corresponding Sector::Value's data section.
- my $r = Scalar::Util::reftype( $value ) || '';
- {
- last if $r eq '';
- last if $r eq 'HASH';
- last if $r eq 'ARRAY';
+=cut
- DBM::Deep->_throw_error(
- "Storage of references of type '$r' is not supported."
- );
- }
+sub read_value { die "read_value must be implemented in a child class" }
- # This will be a Reference sector
- my $sector = $self->_load_sector( $obj->_base_offset )
- or DBM::Deep->_throw_error( "1: Cannot write to a deleted spot in DBM::Deep." );
+=head2 get_classname( $obj )
- if ( $sector->staleness != $obj->_staleness ) {
- DBM::Deep->_throw_error( "2: Cannot write to a deleted spot in DBM::Deep." );
- }
+This takes an object that provides _base_offset() and returns the classname (if
+any) associated with it.
- my ($class, $type);
- if ( !defined $value ) {
- $class = 'DBM::Deep::Engine::Sector::Null';
- }
- elsif ( $r eq 'ARRAY' || $r eq 'HASH' ) {
- my $tmpvar;
- if ( $r eq 'ARRAY' ) {
- $tmpvar = tied @$value;
- } elsif ( $r eq 'HASH' ) {
- $tmpvar = tied %$value;
- }
-
- if ( $tmpvar ) {
- my $is_dbm_deep = eval { local $SIG{'__DIE__'}; $tmpvar->isa( 'DBM::Deep' ); };
-
- unless ( $is_dbm_deep ) {
- DBM::Deep->_throw_error( "Cannot store something that is tied." );
- }
-
- unless ( $tmpvar->_engine->storage == $self->storage ) {
- DBM::Deep->_throw_error( "Cannot store values across DBM::Deep files. Please use export() instead." );
- }
-
- # First, verify if we're storing the same thing to this spot. If we are, then
- # this should be a no-op. -EJS, 2008-05-19
- my $loc = $sector->get_data_location_for({
- key_md5 => $self->_apply_digest( $key ),
- allow_head => 1,
- });
-
- if ( defined($loc) && $loc == $tmpvar->_base_offset ) {
- return 1;
- }
-
- #XXX Can this use $loc?
- my $value_sector = $self->_load_sector( $tmpvar->_base_offset );
- $sector->write_data({
- key => $key,
- key_md5 => $self->_apply_digest( $key ),
- value => $value_sector,
- });
- $value_sector->increment_refcount;
-
- return 1;
- }
-
- $class = 'DBM::Deep::Engine::Sector::Reference';
- $type = substr( $r, 0, 1 );
- }
- else {
- if ( tied($value) ) {
- DBM::Deep->_throw_error( "Cannot store something that is tied." );
- }
- $class = 'DBM::Deep::Engine::Sector::Scalar';
- }
+It delegates to Sector::Reference::get_classname() for the heavy lifting.
- # Create this after loading the reference sector in case something bad happens.
- # This way, we won't allocate value sector(s) needlessly.
- my $value_sector = $class->new({
- engine => $self,
- data => $value,
- type => $type,
- });
-
- $sector->write_data({
- key => $key,
- key_md5 => $self->_apply_digest( $key ),
- value => $value_sector,
- });
-
- # This code is to make sure we write all the values in the $value to the disk
- # and to make sure all changes to $value after the assignment are reflected
- # on disk. This may be counter-intuitive at first, but it is correct dwimmery.
- # NOTE - simply tying $value won't perform a STORE on each value. Hence, the
- # copy to a temp value.
- if ( $r eq 'ARRAY' ) {
- my @temp = @$value;
- tie @$value, 'DBM::Deep', {
- base_offset => $value_sector->offset,
- staleness => $value_sector->staleness,
- storage => $self->storage,
- engine => $self,
- };
- @$value = @temp;
- bless $value, 'DBM::Deep::Array' unless Scalar::Util::blessed( $value );
- }
- elsif ( $r eq 'HASH' ) {
- my %temp = %$value;
- tie %$value, 'DBM::Deep', {
- base_offset => $value_sector->offset,
- staleness => $value_sector->staleness,
- storage => $self->storage,
- engine => $self,
- };
+It performs a staleness check.
- %$value = %temp;
- bless $value, 'DBM::Deep::Hash' unless Scalar::Util::blessed( $value );
- }
+=cut
- return 1;
-}
+sub get_classname { die "get_classname must be implemented in a child class" }
-# XXX Add staleness here
-sub get_next_key {
- my $self = shift;
- my ($obj, $prev_key) = @_;
+=head2 make_reference( $obj, $old_key, $new_key )
- # XXX Need to add logic about resetting the iterator if any key in the reference has changed
- unless ( $prev_key ) {
- $obj->{iterator} = DBM::Deep::Iterator->new({
- base_offset => $obj->_base_offset,
- engine => $self,
- });
- }
+This takes an object that provides _base_offset() and two strings. The
+strings correspond to the old key and new key, respectively. This operation
+is equivalent to (given C<< $db->{foo} = []; >>) C<< $db->{bar} = $db->{foo} >>.
- return $obj->{iterator}->get_next_key( $obj );
-}
+This returns nothing.
-################################################################################
+=cut
-sub setup_fh {
- my $self = shift;
- my ($obj) = @_;
+sub make_reference { die "make_reference must be implemented in a child class" }
- return 1 if $obj->_base_offset;
+=head2 key_exists( $obj, $key )
- my $header = $self->_load_header;
+This takes an object that provides _base_offset() and a string for
+the key to be checked. This returns 1 for true and "" for false.
- # Creating a new file
- if ( $header->is_new ) {
- # 1) Create Array/Hash entry
- my $sector = DBM::Deep::Engine::Sector::Reference->new({
- engine => $self,
- type => $obj->_type,
- });
- $obj->{base_offset} = $sector->offset;
- $obj->{staleness} = $sector->staleness;
+=cut
- $self->flush;
- }
- # Reading from an existing file
- else {
- $obj->{base_offset} = $header->size;
- my $sector = DBM::Deep::Engine::Sector::Reference->new({
- engine => $self,
- offset => $obj->_base_offset,
- });
- unless ( $sector ) {
- DBM::Deep->_throw_error("Corrupted file, no master index record");
- }
+sub key_exists { die "key_exists must be implemented in a child class" }
- unless ($obj->_type eq $sector->type) {
- DBM::Deep->_throw_error("File type mismatch");
- }
+=head2 delete_key( $obj, $key )
- $obj->{staleness} = $sector->staleness;
- }
+This takes an object that provides _base_offset() and a string for
+the key to be deleted. This returns the result of the Sector::Reference
+delete_key() method.
- $self->storage->set_inode;
+=cut
- return 1;
-}
+sub delete_key { die "delete_key must be implemented in a child class" }
-sub begin_work {
- my $self = shift;
- my ($obj) = @_;
+=head2 write_value( $obj, $key, $value )
- if ( $self->trans_id ) {
- DBM::Deep->_throw_error( "Cannot begin_work within an active transaction" );
- }
+This takes an object that provides _base_offset(), a string for the
+key, and a value. This value can be anything storable within L<DBM::Deep>.
- my @slots = $self->read_txn_slots;
- my $found;
- for my $i ( 0 .. $#slots ) {
- next if $slots[$i];
+This returns 1 upon success.
- $slots[$i] = 1;
- $self->set_trans_id( $i + 1 );
- $found = 1;
- last;
- }
- unless ( $found ) {
- DBM::Deep->_throw_error( "Cannot allocate transaction ID" );
- }
- $self->write_txn_slots( @slots );
+=cut
- if ( !$self->trans_id ) {
- DBM::Deep->_throw_error( "Cannot begin_work - no available transactions" );
- }
+sub write_value { die "write_value must be implemented in a child class" }
- return;
-}
+=head2 setup( $obj )
-sub rollback {
- my $self = shift;
- my ($obj) = @_;
+This takes an object that provides _base_offset(). It will do everything needed
+in order to properly initialize all values for necessary functioning. If this is
+called upon an already initialized object, this will also reset the inode.
- if ( !$self->trans_id ) {
- DBM::Deep->_throw_error( "Cannot rollback without an active transaction" );
- }
+This returns 1.
- foreach my $entry ( @{ $self->get_entries } ) {
- my ($sector, $idx) = split ':', $entry;
- $self->_load_sector( $sector )->rollback( $idx );
- }
+=cut
- $self->clear_entries;
+sub setup { die "setup must be implemented in a child class" }
- my @slots = $self->read_txn_slots;
- $slots[$self->trans_id-1] = 0;
- $self->write_txn_slots( @slots );
- $self->inc_txn_staleness_counter( $self->trans_id );
- $self->set_trans_id( 0 );
+=head2 begin_work( $obj )
- return 1;
-}
+This takes an object that provides _base_offset(). It will set up all necessary
+bookkeeping in order to run all work within a transaction.
-sub commit {
- my $self = shift;
- my ($obj) = @_;
+If $obj is already within a transaction, an error wiill be thrown. If there are
+no more available transactions, an error will be thrown.
- if ( !$self->trans_id ) {
- DBM::Deep->_throw_error( "Cannot commit without an active transaction" );
- }
+This returns undef.
- foreach my $entry ( @{ $self->get_entries } ) {
- my ($sector, $idx) = split ':', $entry;
- $self->_load_sector( $sector )->commit( $idx );
- }
+=cut
- $self->clear_entries;
+sub begin_work { die "begin_work must be implemented in a child class" }
- my @slots = $self->read_txn_slots;
- $slots[$self->trans_id-1] = 0;
- $self->write_txn_slots( @slots );
- $self->inc_txn_staleness_counter( $self->trans_id );
- $self->set_trans_id( 0 );
+=head2 rollback( $obj )
- return 1;
-}
+This takes an object that provides _base_offset(). It will revert all
+actions taken within the running transaction.
-sub read_txn_slots {
- my $self = shift;
- return $self->_load_header->read_txn_slots(@_);
-}
+If $obj is not within a transaction, an error will be thrown.
-sub write_txn_slots {
- my $self = shift;
- return $self->_load_header->write_txn_slots(@_);
-}
+This returns 1.
-sub get_running_txn_ids {
- my $self = shift;
- my @transactions = $self->read_txn_slots;
- my @trans_ids = map { $_+1} grep { $transactions[$_] } 0 .. $#transactions;
-}
+=cut
-sub get_txn_staleness_counter {
- my $self = shift;
- return $self->_load_header->get_txn_staleness_counter(@_);
-}
+sub rollback { die "rollback must be implemented in a child class" }
-sub inc_txn_staleness_counter {
- my $self = shift;
- return $self->_load_header->inc_txn_staleness_counter(@_);
-}
+=head2 commit( $obj )
-sub get_entries {
- my $self = shift;
- return [ keys %{ $self->{entries}{$self->trans_id} ||= {} } ];
-}
+This takes an object that provides _base_offset(). It will apply all
+actions taken within the transaction to the HEAD.
-sub add_entry {
- my $self = shift;
- my ($trans_id, $loc, $idx) = @_;
+If $obj is not within a transaction, an error will be thrown.
- $self->{entries}{$trans_id} ||= {};
- $self->{entries}{$trans_id}{"$loc:$idx"} = undef;
-}
+This returns 1.
-# If the buckets are being relocated because of a reindexing, the entries
-# mechanism needs to be made aware of it.
-sub reindex_entry {
- my $self = shift;
- my ($old_loc, $old_idx, $new_loc, $new_idx) = @_;
-
- TRANS:
- while ( my ($trans_id, $locs) = each %{ $self->{entries} } ) {
- if ( exists $locs->{"$old_loc:$old_idx"} ) {
- delete $locs->{"$old_loc:$old_idx"};
- $locs->{"$new_loc:$new_idx"} = undef;
- next TRANS;
- }
- }
-}
+=cut
-sub clear_entries {
- my $self = shift;
- delete $self->{entries}{$self->trans_id};
-}
+sub commit { die "commit must be implemented in a child class" }
-################################################################################
+=head2 get_next_key( $obj, $prev_key )
-sub _apply_digest {
- my $self = shift;
- return $self->{digest}->(@_);
-}
+This takes an object that provides _base_offset() and an optional string
+representing the prior key returned via a prior invocation of this method.
-sub _add_free_blist_sector { shift->_add_free_sector( 0, @_ ) }
-sub _add_free_data_sector { shift->_add_free_sector( 1, @_ ) }
-sub _add_free_index_sector { shift->_add_free_sector( 2, @_ ) }
-sub _add_free_sector { shift->_load_header->add_free_sector( @_ ) }
-
-sub _request_blist_sector { shift->_request_sector( 0, @_ ) }
-sub _request_data_sector { shift->_request_sector( 1, @_ ) }
-sub _request_index_sector { shift->_request_sector( 2, @_ ) }
-sub _request_sector { shift->_load_header->request_sector( @_ ) }
-
-################################################################################
-
-{
- my %t = (
- SIG_ARRAY => 'Reference',
- SIG_HASH => 'Reference',
- SIG_BLIST => 'BucketList',
- SIG_INDEX => 'Index',
- SIG_NULL => 'Null',
- SIG_DATA => 'Scalar',
- );
-
- my %class_for;
- while ( my ($k,$v) = each %t ) {
- $class_for{ DBM::Deep::Engine->$k } = "DBM::Deep::Engine::Sector::$v";
- }
+This method delegates to C<< DBM::Deep::Iterator->get_next_key() >>.
- sub load_sector {
- my $self = shift;
- my ($offset) = @_;
-
- my $data = $self->get_data( $offset )
- or return;#die "Cannot read from '$offset'\n";
- my $type = substr( $$data, 0, 1 );
- my $class = $class_for{ $type };
- return $class->new({
- engine => $self,
- type => $type,
- offset => $offset,
- });
- }
- *_load_sector = \&load_sector;
+=cut
- sub load_header {
- my $self = shift;
+# XXX Add staleness here
+sub get_next_key {
+ my $self = shift;
+ my ($obj, $prev_key) = @_;
- #XXX Does this mean we make too many objects? -RobK, 2008-06-23
- return DBM::Deep::Engine::Sector::FileHeader->new({
- engine => $self,
- offset => 0,
+ # XXX Need to add logic about resetting the iterator if any key in the
+ # reference has changed
+ unless ( defined $prev_key ) {
+ $obj->{iterator} = $self->iterator_class->new({
+ base_offset => $obj->_base_offset,
+ engine => $self,
});
}
- *_load_header = \&load_header;
-
- sub get_data {
- my $self = shift;
- my ($offset, $size) = @_;
- return unless defined $offset;
-
- unless ( exists $self->sector_cache->{$offset} ) {
- # Don't worry about the header sector. It will manage itself.
- return unless $offset;
-
- if ( !defined $size ) {
- my $type = $self->storage->read_at( $offset, 1 )
- or die "($offset): Cannot read from '$offset' to find the type\n";
-
- if ( $type eq $self->SIG_FREE ) {
- return;
- }
-
- my $class = $class_for{$type}
- or die "($offset): Cannot find class for '$type'\n";
- $size = $class->size( $self )
- or die "($offset): '$class' doesn't return a size\n";
- $self->sector_cache->{$offset} = $type . $self->storage->read_at( undef, $size - 1 );
- }
- else {
- $self->sector_cache->{$offset} = $self->storage->read_at( $offset, $size )
- or return;
- }
- }
-
- return \$self->sector_cache->{$offset};
- }
-}
-
-sub sector_cache {
- my $self = shift;
- return $self->{sector_cache} ||= {};
-}
-sub clear_sector_cache {
- my $self = shift;
- $self->{sector_cache} = {};
-}
-
-sub dirty_sectors {
- my $self = shift;
- return $self->{dirty_sectors} ||= {};
-}
-
-sub clear_dirty_sectors {
- my $self = shift;
- $self->{dirty_sectors} = {};
-}
-
-sub add_dirty_sector {
- my $self = shift;
- my ($offset) = @_;
-
- $self->dirty_sectors->{ $offset } = undef;
+ return $obj->{iterator}->get_next_key( $obj );
}
-sub flush {
- my $self = shift;
+=head2 lock_exclusive()
- my $sectors = $self->dirty_sectors;
- for my $offset (sort { $a <=> $b } keys %{ $sectors }) {
- $self->storage->print_at( $offset, $self->sector_cache->{$offset} );
- }
+This takes an object that provides _base_offset(). It will guarantee that
+the storage has taken precautions to be safe for a write.
- # Why do we need to have the storage flush? Shouldn't autoflush take care of things?
- # -RobK, 2008-06-26
- $self->storage->flush;
+This returns nothing.
- $self->clear_dirty_sectors;
-
- $self->clear_sector_cache;
-}
-
-################################################################################
+=cut
sub lock_exclusive {
my $self = shift;
return $self->storage->lock_exclusive( $obj );
}
+=head2 lock_shared()
+
+This takes an object that provides _base_offset(). It will guarantee that
+the storage has taken precautions to be safe for a read.
+
+This returns nothing.
+
+=cut
+
sub lock_shared {
my $self = shift;
my ($obj) = @_;
return $self->storage->lock_shared( $obj );
}
+=head2 unlock()
+
+This takes an object that provides _base_offset(). It will guarantee that
+the storage has released the most recently-taken lock.
+
+This returns nothing.
+
+=cut
+
sub unlock {
my $self = shift;
my ($obj) = @_;
return $rv;
}
-################################################################################
+=head1 INTERNAL METHODS
+
+The following methods are internal-use-only to DBM::Deep::Engine and its
+child classes.
-sub storage { $_[0]{storage} }
-sub byte_size { $_[0]{byte_size} }
-sub hash_size { $_[0]{hash_size} }
-sub hash_chars { $_[0]{hash_chars} }
-sub num_txns { $_[0]{num_txns} }
-sub max_buckets { $_[0]{max_buckets} }
-sub blank_md5 { chr(0) x $_[0]->hash_size }
-sub data_sector_size { $_[0]{data_sector_size} }
+=cut
-# This is a calculated value
-sub txn_bitfield_len {
+=head2 flush()
+
+This takes no arguments. It will do everything necessary to flush all things to
+disk. This is usually called during unlock() and setup().
+
+This returns nothing.
+
+=cut
+
+sub flush {
my $self = shift;
- unless ( exists $self->{txn_bitfield_len} ) {
- my $temp = ($self->num_txns) / 8;
- if ( $temp > int( $temp ) ) {
- $temp = int( $temp ) + 1;
- }
- $self->{txn_bitfield_len} = $temp;
- }
- return $self->{txn_bitfield_len};
+
+ # Why do we need to have the storage flush? Shouldn't autoflush take care of
+ # things? -RobK, 2008-06-26
+ $self->storage->flush;
+
+ return;
}
-sub trans_id { $_[0]{trans_id} }
-sub set_trans_id { $_[0]{trans_id} = $_[1] }
+=head2 load_sector( $loc )
-sub trans_loc { $_[0]{trans_loc} }
-sub set_trans_loc { $_[0]{trans_loc} = $_[1] }
+This takes an id/location/offset and loads the sector based on the engine's
+defined sector type.
-sub chains_loc { $_[0]{chains_loc} }
-sub set_chains_loc { $_[0]{chains_loc} = $_[1] }
+=cut
+
+sub load_sector { $_[0]->sector_type->load( @_ ) }
+
+=head2 cache / clear_cache
+
+This is the cache of loaded Reference sectors.
+
+=cut
sub cache { $_[0]{cache} ||= {} }
sub clear_cache { %{$_[0]->cache} = () }
-sub _dump_file {
- my $self = shift;
- $self->flush;
-
- # Read the header
- my $header_sector = DBM::Deep::Engine::Sector::FileHeader->new({
- engine => $self,
- });
-
- my %types = (
- 0 => 'B',
- 1 => 'D',
- 2 => 'I',
- );
-
- my %sizes = (
- 'D' => $self->data_sector_size,
- 'B' => DBM::Deep::Engine::Sector::BucketList->new({engine=>$self,offset=>1})->size,
- 'I' => DBM::Deep::Engine::Sector::Index->new({engine=>$self,offset=>1})->size,
- );
-
- my $return = "";
-
- # Filesize
- $return .= "Size: " . (-s $self->storage->{fh}) . $/;
-
- # Header values
- $return .= "NumTxns: " . $self->num_txns . $/;
-
- # Read the free sector chains
- my %sectors;
- foreach my $multiple ( 0 .. 2 ) {
- $return .= "Chains($types{$multiple}):";
- my $old_loc = $self->chains_loc + $multiple * $self->byte_size;
- while ( 1 ) {
- my $loc = unpack(
- $StP{$self->byte_size},
- $self->storage->read_at( $old_loc, $self->byte_size ),
- );
-
- # We're now out of free sectors of this kind.
- unless ( $loc ) {
- last;
- }
-
- $sectors{ $types{$multiple} }{ $loc } = undef;
- $old_loc = $loc + SIG_SIZE + $STALE_SIZE;
- $return .= " $loc";
- }
- $return .= $/;
- }
+=head2 supports( $option )
- my $spot = $header_sector->size;
- SECTOR:
- while ( $spot < $self->storage->{end} ) {
- # Read each sector in order.
- my $sector = $self->_load_sector( $spot );
- if ( !$sector ) {
- # Find it in the free-sectors that were found already
- foreach my $type ( keys %sectors ) {
- if ( exists $sectors{$type}{$spot} ) {
- my $size = $sizes{$type};
- $return .= sprintf "%08d: %s %04d\n", $spot, 'F' . $type, $size;
- $spot += $size;
- next SECTOR;
- }
- }
-
- die "********\n$return\nDidn't find free sector for $spot in chains\n********\n";
- }
- else {
- $return .= sprintf "%08d: %s %04d", $spot, $sector->type, $sector->size;
- if ( $sector->type eq 'D' ) {
- $return .= ' ' . $sector->data;
- }
- elsif ( $sector->type eq 'A' || $sector->type eq 'H' ) {
- $return .= ' REF: ' . $sector->get_refcount;
- }
- elsif ( $sector->type eq 'B' ) {
- foreach my $bucket ( $sector->chopped_up ) {
- $return .= "\n ";
- $return .= sprintf "%08d", unpack($StP{$self->byte_size},
- substr( $bucket->[-1], $self->hash_size, $self->byte_size),
- );
- my $l = unpack( $StP{$self->byte_size},
- substr( $bucket->[-1],
- $self->hash_size + $self->byte_size,
- $self->byte_size,
- ),
- );
- $return .= sprintf " %08d", $l;
- foreach my $txn ( 0 .. $self->num_txns - 2 ) {
- my $l = unpack( $StP{$self->byte_size},
- substr( $bucket->[-1],
- $self->hash_size + 2 * $self->byte_size + $txn * ($self->byte_size + $STALE_SIZE),
- $self->byte_size,
- ),
- );
- $return .= sprintf " %08d", $l;
- }
- }
- }
- $return .= $/;
-
- $spot += $sector->size;
- }
- }
+This returns a boolean depending on if this instance of DBM::Dep supports
+that feature. C<$option> can be one of:
- return $return;
-}
+=over 4
+
+=item * transactions
+
+=back
+
+=cut
+
+sub supports { die "supports must be implemented in a child class" }
+
+=head2 ACCESSORS
+
+The following are readonly attributes.
+
+=over 4
+
+=item * storage
+
+=item * sector_type
+
+=back
+
+=cut
+
+sub storage { $_[0]{storage} }
+
+sub sector_type { die "sector_type must be implemented in a child class" }
1;
__END__