Stas Bekman wrote:
tied(%dbm_array)-sync();
I believe that's not enough, because the reader may read data during the
write, resulting in corrupted data read. You have to add locking. see
the DBM chapter in the guide.
You might add MLDBM::Sync to the docs, which easily adds locking
to MLDBM. MLDBM is a front end to store complex data structures
http://www.perl.com/CPAN-local/modules/by-module/MLDBM/CHAMAS/MLDBM-Sync-0.25.readme
What's nice about MLDBM is you can easily swap in out various dbms
like SDBM_File, DB_File, GDBM_File, etc. More recently it even
supports Tie::TextDir too, which provides key per file type storage
which is good when you have a fast file system big data you want
to store.
SYNOPSIS
use MLDBM::Sync; # this gets the default, SDBM_File
use MLDBM qw(DB_File Storable);# use Storable for serializing
use MLDBM qw(MLDBM::Sync::SDBM_File); # use extended SDBM_File, handles values
1024 bytes
use Fcntl qw(:DEFAULT);# import symbols O_CREAT O_RDWR for use
with DBMs
# NORMAL PROTECTED read/write with implicit locks per i/o request
my $sync_dbm_obj = tie %cache, 'MLDBM::Sync' [..other DBM args..] or die $!;
$cache{} = ;
my $value = $cache{};
...
DESCRIPTION
This module wraps around the MLDBM interface, by handling concurrent
access to MLDBM databases with file locking, and flushes i/o explicity
per lock/unlock. The new [Read]Lock()/UnLock() API can be used to
serialize requests logically and improve performance for bundled reads
writes.
Here's some benchmarks on my 2.4.x linux box dual PIII 450 with a couple
7200 RPM IDE drives raid-1 ext3 fs mounted default async.
MLDBM-Sync-0.25]# perl bench/bench_sync.pl
NUMBER OF PROCESSES IN TEST: 4
=== INSERT OF 50 BYTE RECORDS ===
Time for 100 writes + 100 reads for SDBM_File 0.17 seconds
12288 bytes
Time for 100 writes + 100 reads for MLDBM::Sync::SDBM_File 0.20 seconds
12288 bytes
Time for 100 writes + 100 reads for GDBM_File 1.06 seconds
18066 bytes
Time for 100 writes + 100 reads for DB_File0.63 seconds
12288 bytes
Time for 100 writes + 100 reads for Tie::TextDir .04 0.38 seconds
13192 bytes
=== INSERT OF 500 BYTE RECORDS ===
(skipping test for SDBM_File 100 byte limit)
Time for 100 writes + 100 reads for MLDBM::Sync::SDBM_File 0.58 seconds
261120 bytes
Time for 100 writes + 100 reads for GDBM_File 1.09 seconds
63472 bytes
Time for 100 writes + 100 reads for DB_File0.64 seconds
98304 bytes
Time for 100 writes + 100 reads for Tie::TextDir .04 0.33 seconds
58192 bytes
=== INSERT OF 5000 BYTE RECORDS ===
(skipping test for SDBM_File 100 byte limit)
Time for 100 writes + 100 reads for MLDBM::Sync::SDBM_File 1.37 seconds
4128768 bytes
Time for 100 writes + 100 reads for GDBM_File 1.13 seconds
832400 bytes
Time for 100 writes + 100 reads for DB_File1.08 seconds
831488 bytes
Time for 100 writes + 100 reads for Tie::TextDir .04 0.52 seconds
508192 bytes
=== INSERT OF 2 BYTE RECORDS ===
(skipping test for SDBM_File 100 byte limit)
(skipping test for MLDBM::Sync db size 1M)
Time for 100 writes + 100 reads for GDBM_File 1.76 seconds
2063912 bytes
Time for 100 writes + 100 reads for DB_File1.78 seconds
2060288 bytes
Time for 100 writes + 100 reads for Tie::TextDir .04 1.27 seconds
2008192 bytes
=== INSERT OF 5 BYTE RECORDS ===
(skipping test for SDBM_File 100 byte limit)
(skipping test for MLDBM::Sync db size 1M)
Time for 100 writes + 100 reads for GDBM_File 3.52 seconds
5337944 bytes
Time for 100 writes + 100 reads for DB_File3.37 seconds
5337088 bytes
Time for 100 writes + 100 reads for Tie::TextDir .04 2.80 seconds
5008192 bytes
--Josh
_
Joshua Chamas Chamas Enterprises Inc.
NodeWorks Founder Huntington Beach, CA USA
http://www.nodeworks.com1-714-625-4051
