# GDBM_File.pm -- Perl 5 interface to GNU gdbm library. =head1 NAME GDBM_File - Perl5 access to the gdbm library. =head1 SYNOPSIS use GDBM_File; [$db =] tie %hash, 'GDBM_File', $filename, GDBM_WRCREAT, 0640 or die "$GDBM_File::gdbm_errno"; # Use the %hash... $e = $db->errno; $e = $db->syserrno; $str = $db->strerror; $bool = $db->needs_recovery; $db->clear_error; $db->reorganize; $db->sync; $n = $db->count; $n = $db->flags; $str = $db->dbname; $db->cache_size; $db->cache_size($newsize); $n = $db->block_size; $bool = $db->sync_mode; $db->sync_mode($bool); $bool = $db->centfree; $db->centfree($bool); $bool = $db->coalesce; $db->coalesce($bool); $bool = $db->mmap; $size = $db->mmapsize; $db->mmapsize($newsize); $db->recover(%args); untie %hash ; =head1 DESCRIPTION B is a module which allows Perl programs to make use of the facilities provided by the GNU gdbm library. If you intend to use this module you should really have a copy of the B at hand. The manual is avaialble online at L. Most of the B functions are available through the B interface. Unlike Perl's built-in hashes, it is not safe to C the current item from a GDBM_File tied hash while iterating over it with C. This is a limitation of the gdbm library. =head2 Tie Use the Perl buil-in B to associate a B database with a Perl hash: tie %hash, 'GDBM_File', $filename, $flags, $mode; Here, I<$filename> is the name of the database file to open or create. I<$flags> is a bitwise OR of I and optional I. Access mode is one of: =over 4 =item B Open existing database file in read-only mode. =item B Open existing database file in read-write mode. =item B If the database file exists, open it in read-write mode. If it doesn't, create it first and open read-write. =item B Create new database and open it read-write. If the database already exists, truncate it first. =back A number of modifiers can be OR'd to the access mode. Most of them are rarely needed (see L for a complete list), but one is worth mentioning. The B modifier, when used with B, instructs B to create the database in I (so called I) format. This format is best suited for crash-tolerant implementations. See B below for more information. The I<$mode> parameter is the file mode for creating new database file. Use an octal constant or a combination of C constants from the B module. This parameter is used if I<$flags> is B or B. On success, B returns an object of class B. On failure, it returns B. It is recommended to always check the return value, to make sure your hash is successfully associated with the database file. See B below for examples. =head1 STATIC METHODS =head2 GDBM_version $str = GDBM_File->GDBM_version; @ar = GDBM_File->GDBM_version; Returns the version number of the underlying B library. In scalar context, returns the library version formatted as string: MINOR.MAJOR[.PATCH][ (GUESS)] where I, I, and I are version numbers, and I is a guess level (see below). In list context, returns a list: ( MINOR, MAJOR, PATCH [, GUESS] ) The I component is present only if B version is 1.8.3 or earlier. This is because earlier releases of B did not include information about their version and the B module has to implement certain guesswork in order to determine it. I is a textual description in string context, and a positive number indicating how rough the guess is in list context. Possible values are: =over 4 =item 1 - exact guess The major and minor version numbers are guaranteed to be correct. The actual patchlevel is most probably guessed right, but can be 1-2 less than indicated. =item 2 - approximate The major and minor number are guaranteed to be correct. The patchlevel is set to the upper bound. =item 3 - rough guess The version is guaranteed to be not newer than B.I>. =back =head1 ERROR HANDLING =head2 $GDBM_File::gdbm_errno When referenced in numeric context, retrieves the current value of the B variable, i.e. a numeric code describing the state of the most recent operation on any B database. Each numeric code has a symbolic name associated with it. For a comprehensive list of these, see L. Notice, that this list includes all error codes defined for the most recent version of B. Depending on the actual version of the library B is built with, some of these may be missing. In string context, B<$gdbm_errno> returns a human-readable description of the error. If necessary, this description includes the value of B<$!>. This makes it possible to use it in diagnostic messages. For example, the usual tying sequence is tie %hash, 'GDBM_File', $filename, GDBM_WRCREAT, 0640 or die "$GDBM_File::gdbm_errno"; The following, more complex, example illustrates how you can fall back to read-only mode if the database file permissions forbid read-write access: use Errno qw(EACCES); unless (tie(%hash, 'GDBM_File', $filename, GDBM_WRCREAT, 0640)) { if ($GDBM_File::gdbm_errno == GDBM_FILE_OPEN_ERROR && $!{EACCES}) { if (tie(%hash, 'GDBM_File', $filename, GDBM_READER, 0640)) { die "$GDBM_File::gdbm_errno"; } } else { die "$GDBM_File::gdbm_errno"; } } =head2 gdbm_check_syserr if (gdbm_check_syserr(gdbm_errno)) ... Returns true if the system error number (B<$!>) gives more information on the cause of the error. =head1 DATABASE METHODS =head2 close $db->close; Closes the database. Normally you would just do B. However, you will need to use this function if you have explicitly assigned the result of B to a variable, and wish to release the database to another users. Consider the following code: $db = tie %hash, 'GDBM_File', $filename, GDBM_WRCREAT, 0640; # Do something with %hash or $db... untie %hash; $db->close; In this example, doing B alone is not enough, since the database would remain referenced by B<$db>, and, as a consequence, the database file would remain locked. Calling B<$db-Eclose> ensures the database file is closed and unlocked. =head2 errno $db->errno Returns the last error status associated with this database. In string context, returns a human-readable description of the error. See also B<$GDBM_File::gdbm_errno> variable above. =head2 syserrno $db->syserrno Returns the last system error status (C C variable), associated with this database, =head2 strerror $db->strerror Returns textual description of the last error that occurred in this database. =head2 clear_error $db->clear_error Clear error status. =head2 needs_recovery $db->needs_recovery Returns true if the database needs recovery. =head2 reorganize $db->reorganize; Reorganizes the database. =head2 sync $db->sync; Synchronizes recent changes to the database with its disk copy. =head2 count $n = $db->count; Returns number of keys in the database. =head2 flags $db->flags; Returns flags passed as 4th argument to B. =head2 dbname $db->dbname; Returns the database name (i.e. 3rd argument to B. =head2 cache_size $db->cache_size; $db->cache_size($newsize); Returns the size of the internal B cache for that database. Called with argument, sets the size to I<$newsize>. =head2 block_size $db->block_size; Returns the block size of the database. =head2 sync_mode $db->sync_mode; $db->sync_mode($bool); Returns the status of the automatic synchronization mode. Called with argument, enables or disables the sync mode, depending on whether $bool is B or B. When synchronization mode is on (B), any changes to the database are immediately written to the disk. This ensures database consistency in case of any unforeseen errors (e.g. power failures), at the expense of considerable slowdown of operation. Synchronization mode is off by default. =head2 centfree $db->centfree; $db->centfree($bool); Returns status of the central free block pool (B<0> - disabled, B<1> - enabled). With argument, changes its status. By default, central free block pool is disabled. =head2 coalesce $db->coalesce; $db->coalesce($bool); =head2 mmap $db->mmap; Returns true if memory mapping is enabled. This method will B if the B library is complied without memory mapping support. =head2 mmapsize $db->mmapsize; $db->mmapsize($newsize); If memory mapping is enabled, returns the size of memory mapping. With argument, sets the size to B<$newsize>. This method will B if the B library is complied without memory mapping support. =head2 recover $db->recover(%args); Recovers data from a failed database. B<%args> is optional and can contain following keys: =over 4 =item err => sub { ... } Reference to code for detailed error reporting. Upon encountering an error, B will call this sub with a single argument - a description of the error. =item backup => \$str Creates a backup copy of the database before recovery and returns its filename in B<$str>. =item max_failed_keys => $n Maximum allowed number of failed keys. If the actual number becomes equal to I<$n>, B aborts and returns error. =item max_failed_buckets => $n Maximum allowed number of failed buckets. If the actual number becomes equal to I<$n>, B aborts and returns error. =item max_failures => $n Maximum allowed number of failures during recovery. =item stat => \%hash Return recovery statistics in I<%hash>. Upon return, the following keys will be present: =over 8 =item recovered_keys Number of successfully recovered keys. =item recovered_buckets Number of successfully recovered buckets. =item failed_keys Number of keys that failed to be retrieved. =item failed_buckets Number of buckets that failed to be retrieved. =back =back =head2 convert $db->convert($format); Changes the format of the database file referred to by B<$db>. Starting from version 1.20, B supports two database file formats: I and I. The former is the traditional database format, used by previous B versions. The I format contains additional data and is recommended for use in crash tolerant applications. L, for the discussion of both formats. The B<$format> argument sets the new desired database format. It is B to convert the database from standard to extended format, and B<0> to convert it from extended to standard format. If the database is already in the requested format, the function returns success without doing anything. =head2 dump $db->dump($filename, %options) Creates a dump of the database file in I<$filename>. Such file can be used as a backup copy or sent over a wire to recreate the database on another machine. To create a database from the dump file, use the B method. B supports two dump formats: old I and new I. The binary format is not portable across architectures and is deprecated. It is supported for backward compatibility. The ascii format is portable and stores additional meta-data about the file. It was introduced with the B version 1.11 and is the preferred dump format. The B method creates ascii dumps by default. If the named file already exists, the function will refuse to overwrite and will croak an error. If it doesn't exist, it will be created with the mode B<0666> modified by the current B. These defaults can be altered using the following I<%options>: =over 4 =item B => 1 Create dump in I format. =item B => I Set file mode to I. =item B => 1 Silently overwrite existing files. =back =head2 load $db->load($filename, %options) Load the data from the dump file I<$filename> into the database I<$db>. The file must have been previously created using the B method. File format is recognized automatically. By default, the function will croak if the dump contains a key that already exists in the database. It will silently ignore the failure to restore database mode and/or ownership. These defaults can be altered using the following I<%options>: =over 4 =item B => 1 Replace existing keys. =item B => 0 | 1 If I<0>, don't try to restore the mode of the database file to that stored in the dump. =item B => 0 | 1 If I<0>, don't try to restore the owner of the database file to that stored in the dump. =item B => 1 Croak if failed to restore ownership and/or mode. =back The usual sequence to recreate a database from the dump file is: my %hash; my $db = tie %hash, 'GDBM_File', 'a.db', GDBM_NEWDB, 0640; $db->load('a.dump'); =head1 CRASH TOLERANCE Crash tolerance is a new feature that, given appropriate support from the OS and the filesystem, guarantees that a logically consistent recent state of the database can be recovered following a crash, such as power outage, OS kernel panic, or the like. Crash tolerance support appeared in B version 1.21. The theory behind it is explained in "Crashproofing the Original NoSQL Key-Value Store", by Terence Kelly (L). A detailed discussion of the B implementation is available in the B (L). The information below describes the Perl interface. For maximum robustness, we recommend to use I for crash tolerant databases. To create a database in extended format, use the B when opening the database, e.g.: $db = tie %hash, 'GDBM_File', $filename, GDBM_NEWDB|GDBM_NUMSYNC, 0640; To convert existing database to the extended format, use the B method, described above, e.g.: $db->convert(GDBM_NUMSYNC); =head2 crash_tolerance_status GDBM_File->crash_tolerance_status; This static method returns the status of crash tolerance support. A non-zero value means crash tolerance is compiled in and supported by the operating system. =head2 failure_atomic $db->failure_atomic($even, $odd) Enables crash tolerance for the database B<$db>, Arguments are the pathnames of two files that will be created and filled with I of the database file. The two files must not exist when this method is called and must reside on the same filesystem as the database file. This filesystem must be support the I operation (https://www.gnu.org.ua/software/gdbm/manual/Filesystems-supporting-crash-tolerance.html>. After a successful call to B, every call to B<$db->sync> method will make an efficient reflink snapshot of the database file in one of these files; consecutive calls to B alternate between the two, hence the names. The most recent of these files can be used to recover the database after a crash. To select the right snapshot, use the B static method. =head2 latest_snapshot $file = GDBM_File->latest_snapshot($even, $odd); ($file, $error) = GDBM_File->latest_snapshot($even, $odd); Given the two snapshot names (the ones used previously in a call to B), this method selects the one suitable for database recovery, i.e. the file which contains the most recent database snapshot. In scalar context, it returns the selected file name or B in case of failure. In array context, the returns a list of two elements: the file name and status code. On success, the file name is defined and the code is B. On error, the file name is B, and the status is one of the following: =over 4 =item GDBM_SNAPSHOT_BAD Neither snapshot file is applicable. This means that the crash has occurred before a call to B completed. In this case, it is best to fall back on a safe backup copy of the data file. =item GDBM_SNAPSHOT_ERR A system error occurred. Examine B<$!> for details. See for a comprehensive list of error codes and their meaning. =item GDBM_SNAPSHOT_SAME The file modes and modification dates of both snapshot files are exactly the same. This can happen only for databases in standard format. =item GDBM_SNAPSHOT_SUSPICIOUS The I counters of the two snapshots differ by more than one. The most probable reason is programmer's error: the two parameters refer to snapshots belonging to different database files. =back =head1 AVAILABILITY gdbm is available from any GNU archive. The master site is C, but you are strongly urged to use one of the many mirrors. You can obtain a list of mirror sites from L. =head1 SECURITY AND PORTABILITY GDBM files are not portable across platforms. If you wish to transfer a GDBM file over the wire, dump it to a portable format first. B Robustness of GDBM against corrupted databases depends highly on its version. Versions prior to 1.15 did not implement any validity checking, so that a corrupted or maliciously crafted database file could cause perl to crash or even expose a security vulnerability. Versions between 1.15 and 1.20 were progressively strengthened against invalid inputs. Finally, version 1.21 had undergone extensive fuzzy checking which proved its ability to withstand any kinds of inputs without crashing. =head1 SEE ALSO L, L, L, L, L. =cut package GDBM_File; use strict; use warnings; our($VERSION, @ISA, @EXPORT); require Carp; require Tie::Hash; use Exporter 'import'; require XSLoader; @ISA = qw(Tie::Hash); @EXPORT = qw( GDBM_CACHESIZE GDBM_CENTFREE GDBM_COALESCEBLKS GDBM_FAST GDBM_FASTMODE GDBM_INSERT GDBM_NEWDB GDBM_NOLOCK GDBM_OPENMASK GDBM_READER GDBM_REPLACE GDBM_SYNC GDBM_SYNCMODE GDBM_WRCREAT GDBM_WRITER GDBM_NOMMAP GDBM_CLOEXEC GDBM_BSEXACT GDBM_XVERIFY GDBM_PREREAD GDBM_NUMSYNC GDBM_SNAPSHOT_OK GDBM_SNAPSHOT_BAD GDBM_SNAPSHOT_ERR GDBM_SNAPSHOT_SAME GDBM_SNAPSHOT_SUSPICIOUS GDBM_NO_ERROR GDBM_MALLOC_ERROR GDBM_BLOCK_SIZE_ERROR GDBM_FILE_OPEN_ERROR GDBM_FILE_WRITE_ERROR GDBM_FILE_SEEK_ERROR GDBM_FILE_READ_ERROR GDBM_BAD_MAGIC_NUMBER GDBM_EMPTY_DATABASE GDBM_CANT_BE_READER GDBM_CANT_BE_WRITER GDBM_READER_CANT_DELETE GDBM_READER_CANT_STORE GDBM_READER_CANT_REORGANIZE GDBM_UNKNOWN_UPDATE GDBM_ITEM_NOT_FOUND GDBM_REORGANIZE_FAILED GDBM_CANNOT_REPLACE GDBM_ILLEGAL_DATA GDBM_OPT_ALREADY_SET GDBM_OPT_ILLEGAL GDBM_BYTE_SWAPPED GDBM_BAD_FILE_OFFSET GDBM_BAD_OPEN_FLAGS GDBM_FILE_STAT_ERROR GDBM_FILE_EOF GDBM_NO_DBNAME GDBM_ERR_FILE_OWNER GDBM_ERR_FILE_MODE GDBM_UNKNOWN_ERROR GDBM_NEED_RECOVERY GDBM_BACKUP_FAILED GDBM_DIR_OVERFLOW GDBM_BAD_BUCKET GDBM_BAD_HEADER GDBM_BAD_AVAIL GDBM_BAD_HASH_TABLE GDBM_BAD_DIR_ENTRY GDBM_FILE_CLOSE_ERROR GDBM_FILE_SYNC_ERROR GDBM_FILE_TRUNCATE_ERROR GDBM_BUCKET_CACHE_CORRUPTED GDBM_BAD_HASH_ENTRY GDBM_MALFORMED_DATA GDBM_OPT_BADVAL GDBM_ERR_SNAPSHOT_CLONE GDBM_ERR_REALPATH GDBM_ERR_USAGE gdbm_check_syserr ); # This module isn't dual life, so no need for dev version numbers. $VERSION = '1.22'; our $gdbm_errno; XSLoader::load(); 1;