[ новости /+++ | форум | теги | ]

NAME

BerkeleyDB - Perl extension for Berkeley DB version 2, 3 or 4
 

SYNOPSIS

  use BerkeleyDB;

  $env = new BerkeleyDB::Env [OPTIONS] ;

  $db  = tie %hash, 'BerkeleyDB::Hash', [OPTIONS] ;
  $db  = new BerkeleyDB::Hash [OPTIONS] ;

  $db  = tie %hash, 'BerkeleyDB::Btree', [OPTIONS] ;
  $db  = new BerkeleyDB::Btree [OPTIONS] ;

  $db  = tie @array, 'BerkeleyDB::Recno', [OPTIONS] ;
  $db  = new BerkeleyDB::Recno [OPTIONS] ;

  $db  = tie @array, 'BerkeleyDB::Queue', [OPTIONS] ;
  $db  = new BerkeleyDB::Queue [OPTIONS] ;

  $db  = new BerkeleyDB::Unknown [OPTIONS] ;

  $status = BerkeleyDB::db_remove [OPTIONS]
  $status = BerkeleyDB::db_rename [OPTIONS]
  $status = BerkeleyDB::db_verify [OPTIONS]

  $hash{$key} = $value ;
  $value = $hash{$key} ;
  each %hash ;
  keys %hash ;
  values %hash ;

  $status = $db->db_get()
  $status = $db->db_put() ;
  $status = $db->db_del() ;
  $status = $db->db_sync() ;
  $status = $db->db_close() ;
  $status = $db->db_pget()
  $hash_ref = $db->db_stat() ;
  $status = $db->db_key_range();
  $type = $db->type() ;
  $status = $db->status() ;
  $boolean = $db->byteswapped() ;
  $status = $db->truncate($count) ;
  $status = $db->compact($start, $stop, $c_data, $flags, $end);

  $bool = $env->cds_enabled();
  $bool = $db->cds_enabled();
  $lock = $db->cds_lock();
  $lock->cds_unlock();

  ($flag, $old_offset, $old_length) = $db->partial_set($offset, $length) ;
  ($flag, $old_offset, $old_length) = $db->partial_clear() ;

  $cursor = $db->db_cursor([$flags]) ;
  $newcursor = $cursor->c_dup([$flags]);
  $status = $cursor->c_get() ;
  $status = $cursor->c_put() ;
  $status = $cursor->c_del() ;
  $status = $cursor->c_count() ;
  $status = $cursor->c_pget() ;
  $status = $cursor->status() ;
  $status = $cursor->c_close() ;

  $cursor = $db->db_join() ;
  $status = $cursor->c_get() ;
  $status = $cursor->c_close() ;

  $status = $env->txn_checkpoint()
  $hash_ref = $env->txn_stat()
  $status = $env->setmutexlocks()
  $status = $env->set_flags()
  $status = $env->set_timeout()
  $status = $env->lsn_reset()

  $txn = $env->txn_begin() ;
  $db->Txn($txn);
  $txn->Txn($db1, $db2,...);
  $status = $txn->txn_prepare()
  $status = $txn->txn_commit()
  $status = $txn->txn_abort()
  $status = $txn->txn_id()
  $status = $txn->txn_discard()
  $status = $txn->set_timeout()

  $status = $env->set_lg_dir();
  $status = $env->set_lg_bsize();
  $status = $env->set_lg_max();

  $status = $env->set_data_dir() ;
  $status = $env->set_tmp_dir() ;
  $status = $env->set_verbose() ;
  $db_env_ptr = $env->DB_ENV() ;

  $BerkeleyDB::Error
  $BerkeleyDB::db_version

  # DBM Filters
  $old_filter = $db->filter_store_key  ( sub { ... } ) ;
  $old_filter = $db->filter_store_value( sub { ... } ) ;
  $old_filter = $db->filter_fetch_key  ( sub { ... } ) ;
  $old_filter = $db->filter_fetch_value( sub { ... } ) ;

  # deprecated, but supported
  $txn_mgr = $env->TxnMgr();
  $status = $txn_mgr->txn_checkpoint()
  $hash_ref = $txn_mgr->txn_stat()
  $txn = $txn_mgr->txn_begin() ;

DESCRIPTION

This Perl module provides an interface to most of the functionality available in Berkeley DB versions 2, 3 and 4. In general it is safe to assume that the interface provided here to be identical to the Berkeley DB interface. The main changes have been to make the Berkeley DB API work in a Perl way. Note that if you are using Berkeley DB 2.x, the new features available in Berkeley DB 3.x or DB 4.x are not available via this module.

The reader is expected to be familiar with the Berkeley DB documentation. Where the interface provided here is identical to the Berkeley DB library and the... TODO

The db_appinit, db_cursor, db_open and db_txn man pages are particularly relevant.

The interface to Berkeley DB is implemented with a number of Perl classes.  

The BerkeleyDB::Env Class

If you don't intend using transactions, locking or logging, then you shouldn't need to make use of BerkeleyDB::Env.

Note that an environment consists of a number of files that Berkeley DB manages behind the scenes for you. When you first use an environment, it needs to be explicitly created. This is done by including "DB_CREATE" with the "Flags" parameter, described below.  

Synopsis

    $env = new BerkeleyDB::Env
             [ -Home         => $path, ]
             [ -Server       => $name, ]
             [ -CacheSize    => $number, ]
             [ -Config       => { name => value, name => value }, ]
             [ -ErrFile      => filename, ]
             [ -ErrPrefix    => "string", ]
             [ -Flags        => number, ]
             [ -SetFlags     => bitmask, ]
             [ -LockDetect   => number, ]
             [ -SharedMemKey => number, ]
             [ -Verbose      => boolean, ]
             [ -Encrypt      => { Password => "string",
                                  Flags    => number }, ]

All the parameters to the BerkeleyDB::Env constructor are optional.

-Home

If present, this parameter should point to an existing directory. Any files that aren't specified with an absolute path in the sub-systems that are initialised by the BerkeleyDB::Env class will be assumed to live in the Home directory.

For example, in the code fragment below the database ``fred.db'' will be opened in the directory ``/home/databases'' because it was specified as a relative path, but ``joe.db'' will be opened in ``/other'' because it was part of an absolute path.

    $env = new BerkeleyDB::Env
             -Home         => "/home/databases"
    ...

    $db1 = new BerkeleyDB::Hash
             -Filename => "fred.db",
             -Env => $env
    ...

    $db2 = new BerkeleyDB::Hash
             -Filename => "/other/joe.db",
             -Env => $env
    ...

-Server

If present, this parameter should be the hostname of a server that is running the Berkeley DB RPC server. All databases will be accessed via the RPC server.

-Encrypt

If present, this parameter will enable encryption of all data before it is written to the database. This parameters must be given a hash reference. The format is shown below.

    -Encrypt => { -Password => "abc", Flags => DB_ENCRYPT_AES }

Valid values for the Flags are 0 or "DB_ENCRYPT_AES".

This option requires Berkeley DB 4.1 or better.

-Cachesize

If present, this parameter sets the size of the environments shared memory buffer pool.

-SharedMemKey

If present, this parameter sets the base segment ID for the shared memory region used by Berkeley DB.

This option requires Berkeley DB 3.1 or better.

Use "$env->get_shm_key($id)" to find out the base segment ID used once the environment is open.

-Config

This is a variation on the "-Home" parameter, but it allows finer control of where specific types of files will be stored.

The parameter expects a reference to a hash. Valid keys are: DB_DATA_DIR, DB_LOG_DIR and DB_TMP_DIR

The code below shows an example of how it can be used.

    $env = new BerkeleyDB::Env
             -Config => { DB_DATA_DIR => "/home/databases",
                          DB_LOG_DIR  => "/home/logs",
                          DB_TMP_DIR  => "/home/tmp"
                        }
    ...

-ErrFile

Expects a filename or filenhandle. Any errors generated internally by Berkeley DB will be logged to this file. A useful debug setting is to open environments with either

    -ErrFile => *STDOUT

or

    -ErrFile => *STDERR

-ErrPrefix

Allows a prefix to be added to the error messages before they are sent to -ErrFile.

-Flags

The Flags parameter specifies both which sub-systems to initialise, as well as a number of environment-wide options. See the Berkeley DB documentation for more details of these options.

Any of the following can be specified by OR'ing them:

DB_CREATE

If any of the files specified do not already exist, create them.

DB_INIT_CDB

Initialise the Concurrent Access Methods

DB_INIT_LOCK

Initialise the Locking sub-system.

DB_INIT_LOG

Initialise the Logging sub-system.

DB_INIT_MPOOL

Initialise the ...

DB_INIT_TXN

Initialise the ...

DB_MPOOL_PRIVATE

Initialise the ...

DB_INIT_MPOOL is also specified.

Initialise the ...

DB_NOMMAP

Initialise the ...

DB_RECOVER

DB_RECOVER_FATAL

DB_THREAD

DB_TXN_NOSYNC

DB_USE_ENVIRON

DB_USE_ENVIRON_ROOT

-SetFlags

Calls ENV->set_flags with the supplied bitmask. Use this when you need to make use of DB_ENV->set_flags before DB_ENV->open is called.

Only valid when Berkeley DB 3.x or better is used.

-LockDetect

Specifies what to do when a lock conflict occurs. The value should be one of

DB_LOCK_DEFAULT

DB_LOCK_OLDEST

DB_LOCK_RANDOM

DB_LOCK_YOUNGEST

-Verbose

Add extra debugging information to the messages sent to -ErrFile.

Methods

$env->errPrefix(string) ;

This method is identical to the -ErrPrefix flag. It allows the error prefix string to be changed dynamically.

$env->set_flags(bitmask, 1|0);

$txn = $env->TxnMgr()

Constructor for creating a TxnMgr object. See ``TRANSACTIONS'' for more details of using transactions.

This method is deprecated. Access the transaction methods using the txn_ methods below from the environment object directly.

$env->txn_begin()

TODO

$env->txn_stat()

TODO

$env->txn_checkpoint()

TODO

$env->status()

Returns the status of the last BerkeleyDB::Env method.

$env->DB_ENV()

Returns a pointer to the underlying DB_ENV data structure that Berkeley DB uses.

$env->get_shm_key($id)

Writes the base segment ID for the shared memory region used by the Berkeley DB environment into $id. Returns 0 on success.

This option requires Berkeley DB 4.2 or better.

Use the "-SharedMemKey" option when opening the environemt to set the base segment ID.

$env->set_timeout($timeout, $flags)

$env->status()

Returns the status of the last BerkeleyDB::Env method.

Examples

Global Classes

  $status = BerkeleyDB::db_remove [OPTIONS]
  $status = BerkeleyDB::db_rename [OPTIONS]
  $status = BerkeleyDB::db_verify [OPTIONS]

THE DATABASE CLASSES

BerkeleyDB::Hash

This database type allows arbitrary key/value pairs to be stored in data files. This is equivalent to the functionality provided by other hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though, the files created using BerkeleyDB::Hash are not compatible with any of the other packages mentioned.

A default hashing algorithm, which will be adequate for most applications, is built into BerkeleyDB. If you do need to use your own hashing algorithm it is possible to write your own in Perl and have BerkeleyDB use it instead.

BerkeleyDB::Btree

The Btree format allows arbitrary key/value pairs to be stored in a B+tree.

As with the BerkeleyDB::Hash format, it is possible to provide a user defined Perl routine to perform the comparison of keys. By default, though, the keys are stored in lexical order.

BerkeleyDB::Recno

TODO.

BerkeleyDB::Queue

TODO.

BerkeleyDB::Unknown

This isn't a database format at all. It is used when you want to open an existing Berkeley DB database without having to know what type is it.

Each of the database formats described above is accessed via a corresponding BerkeleyDB class. These will be described in turn in the next sections.  

BerkeleyDB::Hash

Two forms of constructor are supported:

    $db = new BerkeleyDB::Hash
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Hash specific
                [ -Ffactor       => number,]
                [ -Nelem         => number,]
                [ -Hash          => code reference,]
                [ -DupCompare    => code reference,]

and this

    [$db =] tie %hash, 'BerkeleyDB::Hash', 
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Hash specific
                [ -Ffactor       => number,]
                [ -Nelem         => number,]
                [ -Hash          => code reference,]
                [ -DupCompare    => code reference,]

When the ``tie'' interface is used, reading from and writing to the database is achieved via the tied hash. In this case the database operates like a Perl associative array that happens to be stored on disk.

In addition to the high-level tied hash interface, it is possible to make use of the underlying methods provided by Berkeley DB  

Options

-Property

Used to specify extra flags when opening a database. The following flags may be specified by bitwise OR'ing together one or more of the following values:

DB_DUP

When creating a new database, this flag enables the storing of duplicate keys in the database. If DB_DUPSORT is not specified as well, the duplicates are stored in the order they are created in the database.

DB_DUPSORT

Enables the sorting of duplicate keys in the database. Ignored if DB_DUP isn't also specified.

-Ffactor

-Nelem

See the Berkeley DB documentation for details of these options.

-Hash

Allows you to provide a user defined hash function. If not specified, a default hash function is used. Here is a template for a user-defined hash function

    sub hash
    {
        my ($data) = shift ;
        ...
        # return the hash value for $data
        return $hash ;
    }

    tie %h, "BerkeleyDB::Hash", 
        -Filename => $filename, 
        -Hash     => \&hash,
        ...

See for an example.

-DupCompare

Used in conjunction with the DB_DUPOSRT flag.

    sub compare
    {
        my ($key, $key2) = @_ ;
        ...
        # return  0 if $key1 eq $key2
        #        -1 if $key1 lt $key2
        #         1 if $key1 gt $key2
        return (-1 , 0 or 1) ;
    }

    tie %h, "BerkeleyDB::Hash", 
        -Filename   => $filename, 
        -Property   => DB_DUP|DB_DUPSORT,
        -DupCompare => \&compare,
        ...

Methods

A Simple Tied Hash Example

    use strict ;
    use BerkeleyDB ;
    use vars qw( %h $k $v ) ;

    my $filename = "fruit" ;
    unlink $filename ;
    tie %h, "BerkeleyDB::Hash",
                -Filename => $filename,
                -Flags    => DB_CREATE
        or die "Cannot open file $filename: $! $BerkeleyDB::Error\n" ;

    # Add a few key/value pairs to the file
    $h{"apple"} = "red" ;
    $h{"orange"} = "orange" ;
    $h{"banana"} = "yellow" ;
    $h{"tomato"} = "red" ;

    # Check for existence of a key
    print "Banana Exists\n\n" if $h{"banana"} ;

    # Delete a key/value pair.
    delete $h{"apple"} ;

    # print the contents of the file
    while (($k, $v) = each %h)
      { print "$k -> $v\n" }

    untie %h ;

here is the output:

    Banana Exists

    orange -> orange
    tomato -> red
    banana -> yellow

Note that the like ordinary associative arrays, the order of the keys retrieved from a Hash database are in an apparently random order.  

Another Simple Hash Example

    use strict ;
    use BerkeleyDB ;

    my $filename = "fruit" ;
    unlink $filename ;
    my $db = new BerkeleyDB::Hash
                -Filename => $filename,
                -Flags    => DB_CREATE
        or die "Cannot open file $filename: $! $BerkeleyDB::Error\n" ;

    # Add a few key/value pairs to the file
    $db->db_put("apple", "red") ;
    $db->db_put("orange", "orange") ;
    $db->db_put("banana", "yellow") ;
    $db->db_put("tomato", "red") ;

    # Check for existence of a key
    print "Banana Exists\n\n" if $db->db_get("banana", $v) == 0;

    # Delete a key/value pair.
    $db->db_del("apple") ;

    # print the contents of the file
    my ($k, $v) = ("", "") ;
    my $cursor = $db->db_cursor() ;
    while ($cursor->c_get($k, $v, DB_NEXT) == 0)
      { print "$k -> $v\n" }

    undef $cursor ;
    undef $db ;

Duplicate keys

    use strict ;
    use BerkeleyDB ;

    my $filename = "fruit" ;
    unlink $filename ;
    my $db = new BerkeleyDB::Hash
                -Filename => $filename,
                -Flags    => DB_CREATE,
                -Property  => DB_DUP
        or die "Cannot open file $filename: $! $BerkeleyDB::Error\n" ;

    # Add a few key/value pairs to the file
    $db->db_put("red", "apple") ;
    $db->db_put("orange", "orange") ;
    $db->db_put("green", "banana") ;
    $db->db_put("yellow", "banana") ;
    $db->db_put("red", "tomato") ;
    $db->db_put("green", "apple") ;

    # print the contents of the file
    my ($k, $v) = ("", "") ;
    my $cursor = $db->db_cursor() ;
    while ($cursor->c_get($k, $v, DB_NEXT) == 0)
      { print "$k -> $v\n" }

    undef $cursor ;
    undef $db ;

here is the output:

    orange -> orange
    yellow -> banana
    red -> apple
    red -> tomato
    green -> banana
    green -> apple

Sorting Duplicate Keys

    use strict ;
    use BerkeleyDB ;

    my $filename = "fruit" ;
    unlink $filename ;
    my $db = new BerkeleyDB::Hash
                -Filename => $filename,
                -Flags    => DB_CREATE,
                -Property  => DB_DUP | DB_DUPSORT
        or die "Cannot open file $filename: $! $BerkeleyDB::Error\n" ;

    # Add a few key/value pairs to the file
    $db->db_put("red", "apple") ;
    $db->db_put("orange", "orange") ;
    $db->db_put("green", "banana") ;
    $db->db_put("yellow", "banana") ;
    $db->db_put("red", "tomato") ;
    $db->db_put("green", "apple") ;

    # print the contents of the file
    my ($k, $v) = ("", "") ;
    my $cursor = $db->db_cursor() ;
    while ($cursor->c_get($k, $v, DB_NEXT) == 0)
      { print "$k -> $v\n" }

    undef $cursor ;
    undef $db ;

Notice that in the output below the duplicate values are sorted.

    orange -> orange
    yellow -> banana
    red -> apple
    red -> tomato
    green -> apple
    green -> banana

Custom Sorting Duplicate Keys

TODO  

Changing the hash

Using db_stat

BerkeleyDB::Btree

Two forms of constructor are supported:

    $db = new BerkeleyDB::Btree
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Btree specific
                [ -Minkey        => number,]
                [ -Compare       => code reference,]
                [ -DupCompare    => code reference,]
                [ -Prefix        => code reference,]

and this

    [$db =] tie %hash, 'BerkeleyDB::Btree', 
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Btree specific
                [ -Minkey        => number,]
                [ -Compare       => code reference,]
                [ -DupCompare    => code reference,]
                [ -Prefix        => code reference,]

Options

-Property

Used to specify extra flags when opening a database. The following flags may be specified by bitwise OR'ing together one or more of the following values:

DB_DUP

When creating a new database, this flag enables the storing of duplicate keys in the database. If DB_DUPSORT is not specified as well, the duplicates are stored in the order they are created in the database.

DB_DUPSORT

Enables the sorting of duplicate keys in the database. Ignored if DB_DUP isn't also specified.

Minkey

TODO

Compare

Allow you to override the default sort order used in the database. See ``Changing the sort order'' for an example.

    sub compare
    {
        my ($key, $key2) = @_ ;
        ...
        # return  0 if $key1 eq $key2
        #        -1 if $key1 lt $key2
        #         1 if $key1 gt $key2
        return (-1 , 0 or 1) ;
    }

    tie %h, "BerkeleyDB::Hash", 
        -Filename   => $filename, 
        -Compare    => \&compare,
        ...

Prefix

    sub prefix
    {
        my ($key, $key2) = @_ ;
        ...
        # return number of bytes of $key2 which are 
        # necessary to determine that it is greater than $key1
        return $bytes ;
    }

    tie %h, "BerkeleyDB::Hash", 
        -Filename   => $filename, 
        -Prefix     => \&prefix,
        ...
=item DupCompare

    sub compare
    {
        my ($key, $key2) = @_ ;
        ...
        # return  0 if $key1 eq $key2
        #        -1 if $key1 lt $key2
        #         1 if $key1 gt $key2
        return (-1 , 0 or 1) ;
    }

    tie %h, "BerkeleyDB::Hash", 
        -Filename   => $filename, 
        -DupCompare => \&compare,
        ...

Methods

All the methods below return 0 to indicate success.

$status = $db->db_key_range($key, $less, $equal, $greater [, $flags])

Given a key, $key, this method returns the proportion of keys less than $key in $less, the proportion equal to $key in $equal and the proportion greater than $key in $greater.

The proportion is returned as a double in the range 0.0 to 1.0.

A Simple Btree Example

    use strict ;
    use BerkeleyDB ;

    my $filename = "tree" ;
    unlink $filename ;
    my %h ;
    tie %h, 'BerkeleyDB::Btree',
                -Filename   => $filename,
                -Flags      => DB_CREATE
      or die "Cannot open $filename: $! $BerkeleyDB::Error\n" ;

    # Add a key/value pair to the file
    $h{'Wall'} = 'Larry' ;
    $h{'Smith'} = 'John' ;
    $h{'mouse'} = 'mickey' ;
    $h{'duck'}  = 'donald' ;

    # Delete
    delete $h{"duck"} ;

    # Cycle through the keys printing them in order.
    # Note it is not necessary to sort the keys as
    # the btree will have kept them in order automatically.
    foreach (keys %h)
      { print "$_\n" }

    untie %h ;

Here is the output from the code above. The keys have been sorted using Berkeley DB's default sorting algorithm.

    Smith
    Wall
    mouse

Changing the sort order

    use strict ;
    use BerkeleyDB ;

    my $filename = "tree" ;
    unlink $filename ;
    my %h ;
    tie %h, 'BerkeleyDB::Btree',
                -Filename   => $filename,
                -Flags      => DB_CREATE,
                -Compare    => sub { lc $_[0] cmp lc $_[1] }
      or die "Cannot open $filename: $!\n" ;

    # Add a key/value pair to the file
    $h{'Wall'} = 'Larry' ;
    $h{'Smith'} = 'John' ;
    $h{'mouse'} = 'mickey' ;
    $h{'duck'}  = 'donald' ;

    # Delete
    delete $h{"duck"} ;

    # Cycle through the keys printing them in order.
    # Note it is not necessary to sort the keys as
    # the btree will have kept them in order automatically.
    foreach (keys %h)
      { print "$_\n" }

    untie %h ;

Here is the output from the code above.

    mouse
    Smith
    Wall

There are a few point to bear in mind if you want to change the ordering in a BTREE database:

1.

The new compare function must be specified when you create the database.

2.

You cannot change the ordering once the database has been created. Thus you must use the same compare function every time you access the database.

Using db_stat

BerkeleyDB::Recno

Two forms of constructor are supported:

    $db = new BerkeleyDB::Recno
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Recno specific
                [ -Delim           => byte,]
                [ -Len             => number,]
                [ -Pad             => byte,]
                [ -Source          => filename,]

and this

    [$db =] tie @arry, 'BerkeleyDB::Recno', 
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Recno specific
                [ -Delim           => byte,]
                [ -Len             => number,]
                [ -Pad             => byte,]
                [ -Source          => filename,]

A Recno Example

    use strict ;
    use BerkeleyDB ;

    my $filename = "text" ;
    unlink $filename ;

    my @h ;
    tie @h, 'BerkeleyDB::Recno',
                -Filename   => $filename,
                -Flags      => DB_CREATE,
                -Property   => DB_RENUMBER
      or die "Cannot open $filename: $!\n" ;

    # Add a few key/value pairs to the file
    $h[0] = "orange" ;
    $h[1] = "blue" ;
    $h[2] = "yellow" ;

    push @h, "green", "black" ;

    my $elements = scalar @h ;
    print "The array contains $elements entries\n" ;

    my $last = pop @h ;
    print "popped $last\n" ;

    unshift @h, "white" ;
    my $first = shift @h ;
    print "shifted $first\n" ;

    # Check for existence of a key
    print "Element 1 Exists with value $h[1]\n" if $h[1] ;

    untie @h ;

Here is the output from the script:

    The array contains 5 entries
    popped black
    shifted white
    Element 1 Exists with value blue
    The last element is green
    The 2nd last element is yellow

BerkeleyDB::Queue

Two forms of constructor are supported:

    $db = new BerkeleyDB::Queue
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Queue specific
                [ -Len             => number,]
                [ -Pad             => byte,]
                [ -ExtentSize    => number, ]

and this

    [$db =] tie @arry, 'BerkeleyDB::Queue', 
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],
                # BerkeleyDB::Queue specific
                [ -Len             => number,]
                [ -Pad             => byte,]

BerkeleyDB::Unknown

Equivalent to calling db_open with type DB_UNKNOWN in Berkeley DB 2.x and calling db_create followed by DB->open with type DB_UNKNOWN in Berkeley DB 3.x or greater.

The constructor looks like this:

    $db = new BerkeleyDB::Unknown
                [ -Filename      => "filename", ]
                [ -Subname       => "sub-database name", ]
                [ -Flags         => flags,]
                [ -Property      => flags,]
                [ -Mode          => number,]
                [ -Cachesize     => number,]
                [ -Lorder        => number,]
                [ -Pagesize      => number,]
                [ -Env           => $env,]
                [ -Txn           => $txn,]
                [ -Encrypt       => { Password => "string",
                                      Flags    => number }, ],

An example

COMMON OPTIONS

-Filename

The database filename. If no filename is specified, a temporary file will be created and removed once the program terminates.

-Subname

Specifies the name of the sub-database to open. This option is only valid if you are using Berkeley DB 3.x or greater.

-Flags

Specify how the database will be opened/created. The valid flags are:

DB_CREATE

Create any underlying files, as necessary. If the files do not already exist and the DB_CREATE flag is not specified, the call will fail.

DB_NOMMAP

Not supported by BerkeleyDB.

DB_RDONLY

Opens the database in read-only mode.

DB_THREAD

Not supported by BerkeleyDB.

DB_TRUNCATE

If the database file already exists, remove all the data before opening it.

-Mode

Determines the file protection when the database is created. Defaults to 0666.

-Cachesize

-Lorder

-Pagesize

-Env

When working under a Berkeley DB environment, this parameter

Defaults to no environment.

-Encrypt

If present, this parameter will enable encryption of all data before it is written to the database. This parameters must be given a hash reference. The format is shown below.

    -Encrypt => { -Password => "abc", Flags => DB_ENCRYPT_AES }

Valid values for the Flags are 0 or "DB_ENCRYPT_AES".

This option requires Berkeley DB 4.1 or better.

-Txn

TODO.

COMMON DATABASE METHODS

All the methods below return 0 to indicate success.  

$status = $db->db_get($key, $value [, $flags])

The $flags parameter is optional. If present, it must be set to one of the following values:

DB_GET_BOTH

When the DB_GET_BOTH flag is specified, db_get checks for the existence of both the $key and $value in the database.

DB_SET_RECNO

TODO.

In addition, the following value may be set by bitwise OR'ing it into the $flags parameter:

DB_RMW

TODO

$status = $db->db_put($key, $value [, $flags])

The $flags parameter is optional. If present it must be set to one of the following values:

DB_APPEND

This flag is only applicable when accessing a BerkeleyDB::Recno database.

TODO.

DB_NOOVERWRITE

If this flag is specified and $key already exists in the database, the call to db_put will return DB_KEYEXIST.

$status = $db->db_del($key [, $flags])

The $flags parameter is optional and is currently unused.  

$status = $db->db_sync()

$cursor = $db->db_cursor([$flags])

The $flags parameter is optional. If present it must be set to one of the following values:

DB_RMW

TODO.

($flag, $old_offset, $old_length) = $db->partial_set($offset, $length) ;

($flag, $old_offset, $old_length) = $db->partial_clear() ;

$db->byteswapped()

$db->type()

$bool = $env->cds_enabled();

$bool = $db->cds_enabled();

$lock = $db->cds_lock();

It is a fatal error to attempt to create a cds_lock if the Berkeley DB environment has not been opened in CDS mode.  

$lock->cds_unlock();

Note that if multiple CDS lock objects are created, the underlying write lock will not be released until all CDS lock objects are either explictly unlocked with this method, or the CDS lock objects have been destroyed.  

$ref = $db->db_stat()

    $version = $ref->{'bt_version'} ;

If you are using Berkeley DB 3.x or better, this method will work will all database formats. When DB 2.x is used, it only works with BerkeleyDB::Btree.  

$status = $db->status()

$status = $db->truncate($count)

$status = $db->compact($start, $stop, $c_data, $flags, $end);

All the parameters are optional - if only want to make use of some of them, use "undef" for those you don't want. Trailing unusused parameters can be omitted. For example, if you only want to use the $c_data parameter to set the "compact_fillpercent", write you code like this

    my %hash;
    $hash{compact_fillpercent} = 50;
    $db->commit(undef, undef, \%hash);

The parameters operate identically to the C equivalent of this method. The $c_data needs a bit of explanation - it must be a hash reference. The values of the following keys can be set before calling "compact" and will affect the operation of the compaction.

The following keys, along with associated values, will be created in the hash reference if the "compact" operation was successful.

* compact_deadlock =item * compact_levels =item * compact_pages_free =item * compact_pages_examine =item * compact_pages_truncated

You need to be running Berkeley DB 4.4 or better if you wan to make use of "compact".  

CURSORS

A cursor object has the following methods available:  

$newcursor = $cursor->c_dup($flags)

The $flags parameter is optional and can take the following value:

DB_POSITION

When present this flag will position the new cursor at the same place as the existing cursor.

$status = $cursor->c_get($key, $value, $flags)

DB_FIRST

Set the cursor to point to the first key/value pair in the database. Return the key/value pair in $key and $value.

DB_LAST

Set the cursor to point to the last key/value pair in the database. Return the key/value pair in $key and $value.

DB_NEXT

If the cursor is already pointing to a key/value pair, it will be incremented to point to the next key/value pair and return its contents.

If the cursor isn't initialised, DB_NEXT works just like DB_FIRST.

If the cursor is already positioned at the last key/value pair, c_get will return DB_NOTFOUND.

DB_NEXT_DUP

This flag is only valid when duplicate keys have been enabled in a database. If the cursor is already pointing to a key/value pair and the key of the next key/value pair is identical, the cursor will be incremented to point to it and their contents returned.

DB_PREV

If the cursor is already pointing to a key/value pair, it will be decremented to point to the previous key/value pair and return its contents.

If the cursor isn't initialised, DB_PREV works just like DB_LAST.

If the cursor is already positioned at the first key/value pair, c_get will return DB_NOTFOUND.

DB_CURRENT

If the cursor has been set to point to a key/value pair, return their contents. If the key/value pair referenced by the cursor has been deleted, c_get will return DB_KEYEMPTY.

DB_SET

Set the cursor to point to the key/value pair referenced by $key and return the value in $value.

DB_SET_RANGE

This flag is a variation on the DB_SET flag. As well as returning the value, it also returns the key, via $key. When used with a BerkeleyDB::Btree database the key matched by c_get will be the shortest key (in length) which is greater than or equal to the key supplied, via $key. This allows partial key searches. See ??? for an example of how to use this flag.

DB_GET_BOTH

Another variation on DB_SET. This one returns both the key and the value.

DB_SET_RECNO

TODO.

DB_GET_RECNO

TODO.

In addition, the following value may be set by bitwise OR'ing it into the $flags parameter:

DB_RMW

TODO.

$status = $cursor->c_put($key, $value, $flags)

DB_AFTER

When used with a Btree or Hash database, a duplicate of the key referenced by the current cursor position will be created and the contents of $value will be associated with it - $key is ignored. The new key/value pair will be stored immediately after the current cursor position. Obviously the database has to have been opened with DB_DUP.

When used with a Recno ... TODO

DB_BEFORE

When used with a Btree or Hash database, a duplicate of the key referenced by the current cursor position will be created and the contents of $value will be associated with it - $key is ignored. The new key/value pair will be stored immediately before the current cursor position. Obviously the database has to have been opened with DB_DUP.

When used with a Recno ... TODO

DB_CURRENT

If the cursor has been initialised, replace the value of the key/value pair stored in the database with the contents of $value.

DB_KEYFIRST

Only valid with a Btree or Hash database. This flag is only really used when duplicates are enabled in the database and sorted duplicates haven't been specified. In this case the key/value pair will be inserted as the first entry in the duplicates for the particular key.

DB_KEYLAST

Only valid with a Btree or Hash database. This flag is only really used when duplicates are enabled in the database and sorted duplicates haven't been specified. In this case the key/value pair will be inserted as the last entry in the duplicates for the particular key.

$status = $cursor->c_del([$flags])

If the key/value pair associated with the cursor have already been deleted, c_del will return DB_KEYEMPTY.

The $flags parameter is not used at present.  

$status = $cursor->c_count($cnt [, $flags])

The $flags parameter is not used at present. This method needs Berkeley DB 3.1 or better.  

$status = $cursor->status()

$status = $cursor->c_pget() ;

$status = $cursor->c_close()

Cursor Examples

Iterating from first to last, then in reverse.

examples of each of the flags.  

JOIN

TODO  

TRANSACTIONS

CDS Mode

DBM Filters

There are four methods associated with DBM Filters. All work identically, and each is used to install (or uninstall) a single DBM Filter. Each expects a single parameter, namely a reference to a sub. The only difference between them is the place that the filter is installed.

To summarise:

filter_store_key

If a filter has been installed with this method, it will be invoked every time you write a key to a DBM database.

filter_store_value

If a filter has been installed with this method, it will be invoked every time you write a value to a DBM database.

filter_fetch_key

If a filter has been installed with this method, it will be invoked every time you read a key from a DBM database.

filter_fetch_value

If a filter has been installed with this method, it will be invoked every time you read a value from a DBM database.

You can use any combination of the methods, from none, to all four.

All filter methods return the existing filter, if present, or "undef" in not.

To delete a filter pass "undef" to it.  

The Filter

An Example --- the NULL termination problem.

    $hash{"$key\0"} = "$value\0" ;

Similarly the NULL needs to be taken into account when you are considering the length of existing keys/values.

It would be much better if you could ignore the NULL terminations issue in the main application code and have a mechanism that automatically added the terminating NULL to all keys and values whenever you write to the database and have them removed when you read from the database. As I'm sure you have already guessed, this is a problem that DBM Filters can fix very easily.

    use strict ;
    use BerkeleyDB ;

    my %hash ;
    my $filename = "filt.db" ;
    unlink $filename ;

    my $db = tie %hash, 'BerkeleyDB::Hash',
                -Filename   => $filename,
                -Flags      => DB_CREATE
      or die "Cannot open $filename: $!\n" ;

    # Install DBM Filters
    $db->filter_fetch_key  ( sub { s/\0$//    } ) ;
    $db->filter_store_key  ( sub { $_ .= "\0" } ) ;
    $db->filter_fetch_value( sub { s/\0$//    } ) ;
    $db->filter_store_value( sub { $_ .= "\0" } ) ;

    $hash{"abc"} = "def" ;
    my $a = $hash{"ABC"} ;
    # ...
    undef $db ;
    untie %hash ;

Hopefully the contents of each of the filters should be self-explanatory. Both ``fetch'' filters remove the terminating NULL, and both ``store'' filters add a terminating NULL.  

Another Example --- Key is a C int.

    $hash{12345} = "something" ;

the key 12345 will get stored in the DBM database as the 5 byte string ``12345''. If you actually want the key to be stored in the DBM database as a C int, you will have to use "pack" when writing, and "unpack" when reading.

Here is a DBM Filter that does it:

    use strict ;
    use BerkeleyDB ;
    my %hash ;
    my $filename = "filt.db" ;
    unlink $filename ;

    my $db = tie %hash, 'BerkeleyDB::Btree',
                -Filename   => $filename,
                -Flags      => DB_CREATE
      or die "Cannot open $filename: $!\n" ;

    $db->filter_fetch_key  ( sub { $_ = unpack("i", $_) } ) ;
    $db->filter_store_key  ( sub { $_ = pack ("i", $_) } ) ;
    $hash{123} = "def" ;
    # ...
    undef $db ;
    untie %hash ;

This time only two filters have been used --- we only need to manipulate the contents of the key, so it wasn't necessary to install any value filters.  

Using BerkeleyDB with MLDBM

    use strict ;
    use BerkeleyDB ;
    use MLDBM qw(BerkeleyDB::Btree) ;
    use Data::Dumper;

    my $filename = 'testmldbm' ;
    my %o ;

    unlink $filename ;
    tie %o, 'MLDBM', -Filename => $filename,
                     -Flags    => DB_CREATE
                    or die "Cannot open database '$filename: $!\n";

See the MLDBM documentation for information on how to use the module and for details of its limitations.  

EXAMPLES

HINTS & TIPS

Sharing Databases With C Applications

The vast majority of problems that are reported in this area boil down to the fact that C strings are NULL terminated, whilst Perl strings are not. See ``An Example --- the NULL termination problem.'' in the DBM FILTERS section for a generic way to work around this problem.  

The untie Gotcha

COMMON QUESTIONS

Relationship with DB_File

How do I store Perl data structures with BerkeleyDB?

HISTORY

AVAILABILITY

The official web site for Berkeley DB is http://www.sleepycat.com.  

COPYRIGHT

Although BerkeleyDB is covered by the Perl license, the library it makes use of, namely Berkeley DB, is not. Berkeley DB has its own copyright and its own license. Please take the time to read it.

Here are few words taken from the Berkeley DB FAQ (at http://www.sleepycat.com) regarding the license:

    Do I have to license DB to use it in Perl scripts?

    No. The Berkeley DB license requires that software that uses
    Berkeley DB be freely redistributable. In the case of Perl, that
    software is Perl, and not your scripts. Any Perl scripts that you
    write are your property, including scripts that make use of Berkeley
    DB. Neither the Perl license nor the Berkeley DB license
    place any restriction on what you may do with them.

If you are in any doubt about the license situation, contact either the Berkeley DB authors or the author of BerkeleyDB. See ``AUTHOR'' for details.  

AUTHOR

Questions about Berkeley DB may be addressed to <db@sleepycat.com>.  

SEE ALSO

Index

NAME

SYNOPSIS

DESCRIPTION

The BerkeleyDB::Env Class

Synopsis

Methods

Examples

Global Classes

THE DATABASE CLASSES

BerkeleyDB::Hash

Options

Methods

A Simple Tied Hash Example

Another Simple Hash Example

Duplicate keys

Sorting Duplicate Keys

Custom Sorting Duplicate Keys

Changing the hash

Using db_stat

BerkeleyDB::Btree

Options

Methods

A Simple Btree Example

Changing the sort order

Using db_stat

BerkeleyDB::Recno

A Recno Example

BerkeleyDB::Queue

BerkeleyDB::Unknown

An example

COMMON OPTIONS

COMMON DATABASE METHODS

$status = $db->db_get($key, $value [, $flags])

$status = $db->db_put($key, $value [, $flags])

$status = $db->db_del($key [, $flags])

$status = $db->db_sync()

$cursor = $db->db_cursor([$flags])

($flag, $old_offset, $old_length) = $db->partial_set($offset, $length) ;

($flag, $old_offset, $old_length) = $db->partial_clear() ;

$db->byteswapped()

$db->type()

$bool = $env->cds_enabled();

$bool = $db->cds_enabled();

$lock = $db->cds_lock();

$lock->cds_unlock();

$ref = $db->db_stat()

$status = $db->status()

$status = $db->truncate($count)

$status = $db->compact($start, $stop, $c_data, $flags, $end);

CURSORS

$newcursor = $cursor->c_dup($flags)

$status = $cursor->c_get($key, $value, $flags)

$status = $cursor->c_put($key, $value, $flags)

$status = $cursor->c_del([$flags])

$status = $cursor->c_count($cnt [, $flags])

$status = $cursor->status()

$status = $cursor->c_pget() ;

$status = $cursor->c_close()

Cursor Examples

JOIN

TRANSACTIONS

CDS Mode

DBM Filters

The Filter

An Example --- the NULL termination problem.

Another Example --- Key is a C int.

Using BerkeleyDB with MLDBM

EXAMPLES

HINTS & TIPS

Sharing Databases With C Applications

The untie Gotcha

COMMON QUESTIONS

Relationship with DB_File

How do I store Perl data structures with BerkeleyDB?

HISTORY

AVAILABILITY

COPYRIGHT

AUTHOR

SEE ALSO

---

Поиск по тексту MAN-ов: 

Партнёры:

Хостинг:

Закладки на сайте Проследить за страницей

Created 1996-2024 by Maxim Chirkov Добавить, Поддержать, Вебмастеру