Storable 0.6 Copyright (c) 1995-1998, Raphael Manfredi ------------------------------------------------------------------------ This program is free software; you can redistribute it and/or modify it under the terms of the Artistic License, a copy of which can be found with perl. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Artistic License for more details. ------------------------------------------------------------------------ *** This is beta software -- use at your own risks *** IMPORTANT: The serialization format changed between 0.5 and 0.6, and is NOT backward compatible. Think about it when upgrading from a pre-0.5@9 version -- images from versions 0.5@9 are still supported. The Storable extension brings persistency to your data. You may recursively store to disk any data structure, no matter how complex and circular it is, provided it contains only SCALAR, ARRAY, HASH and references to those items, blessed or not. At a later stage, or in another program, you may retrieve data from the stored file and recreate the same hiearchy in memory. If you had blessed references, the retrieved references are blessed into the same package, so you must make sure you have access to the same perl class than the one used to create the relevant objects. For instance: use Storable; $scalar = 'scalar'; $hash{$scalar} = 'value'; $ref = \%hash; @array = ('first', undef, $scalar, $ref, \$ref); &show(\@array); store(\@array, 'store'); $root = retrieve('store'); print '-' x 10, "\n"; &show($root) if ref($root) eq 'ARRAY'; sub show { my ($aref) = @_; foreach $i (@{$aref}) { unless (defined $i) { print "undef\n"; next; } print "$i"; print " ($$i)" if ref($i) eq 'SCALAR'; print "\n"; } } when run on my machine produces: first undef scalar HASH(0x4001eec0) SCALAR(0x4001ee60) ---------- first undef scalar HASH(0x40021fd4) SCALAR(0x40017008) You can see that items are retrieved in memory at some other place, but the topology of the retrieved data is the same as the original. I had first written Storable in Perl, but the results were disappointing, because it took almost 20 seconds to store 200K worth of data. By having the heart of Storable in C, I can store the same amount of data in about 0.6 seconds. To retrieve the same data, it takes roughly 1.0 seconds, because you have to allocate objects in memory whereas storing merely traverses structures. More accurately, using Benchmark, I get (for a 236802 byte long stored file): Machine Time to store Time to retrieve (cpu + sys) (cpu + sys) HP 9000/712 0.61 s 1.02 s HP 9000/856 0.33 s 0.39 s To store/retrieve the "Magic: The Gathering" (MTG) database (1.9 Mb) in native format: Machine Time to store Time to retrieve (cpu + sys) (cpu + sys) HP 9000/712 1.95 s 2.19 s That's roughly 1Mb/s for store and 0.86Mb/s for retrieve. NOTE: The above figures were valid for Storable-0.5 and earlier. No similar benchmarking have been made with Storable-0.6 and higher, which use a different binary image. Comparison of Storable-0.5@9 and Storable-0.6@3 on a version of Tom Christiansen's MTG database (1.8 Mb in native 0.5 format, 1.6 Mb only in 0.6 format) gives: Version Storable Image "store" "nstore" "retrieve" Size in Mb in Kb/s in Kb/s in Kb/s 0.5@9 1.817 801 701 692 0.6@3 1.526 880 851 870 Kb/s rates refer to the size of the Storable image. Since the image is shorter with version 0.6, we must normalize the results to compare relative speed correctly, and therefore measure the overall time it takes to store/retrieve the same database. We get: Version Storable Image "store" "nstore" "retrieve" Size in Mb in secs in secs in secs 0.5@9 1.817 2.32 2.65 2.69 0.6@3 1.526 1.78 1.84 1.80 Notice the important gain at retrieval time, due to the fact that we now use an array instead of a hash table to keep track of retrieved objects. I have no explaination for the relative speed-up of nstore operations other than the fact that less tests for "netorder" are made. To compile this extension, run: perl Makefile.PL [PERL_SRC=...where you put perl sources...] make make install There is an embeded POD manual page in Storable.pm. Raphael Manfredi Thanks to: Jarkko Hietaniemi Ulrich Pfeifer Benjamin A. Holzman Andrew Ford Gisle Aas Jeff Gresham Murray Nesbitt Albert N. Micheev for their contributions. There is a Japanese translation of this man page available at http://member.nifty.ne.jp/hippo2000/perltips/storable.htm, courtesy of Kawai, Takanori .