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List:       apache-modperl
Subject:    Re: mod_perl shared memory with MM
From:       Joshua Chamas <joshua () chamas ! com>
Date:       2001-02-28 16:25:47
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Adi Fairbank wrote:
> 
> I am trying to squeeze more performance out of my persistent session cache.  In
> my application, the Storable image size of my sessions can grow upwards of
> 100-200K.  It can take on the order of 200ms for Storable to deserialize and
> serialize this on my (lousy) hardware.
> 

Its a different approach, but I use simple MLDBM + SDBM_File 
when possible, as its really fast for small records, but it has
that 1024 byte limit per record!  I am releasing a wrapper
to CPAN ( on its way now ) called MLDBM::Sync that handles
concurrent locking & i/o flushing for you.  One advantage
of this approach is that your session state will persist
through a server reboot if its written to disk.

I also wrote a wrapper for SDBM_File called MLDBM::Sync::SDBM_File
that overcomes the 1024 byte limit per record.  The below 
numbers were for a benchmark on my dual PIII 450, linux 2.2.14,
SCSI raid-1 ext2 fs mounted async.  The benchmark can be found
in the MLDBM::Sync package in the bench directory once it makes
it to CPAN.

With MLDBM ( perldoc MLDBM ) you can use Storable or 
XS Data::Dumper method for serialization as well as 
various DBMs.

--Josh

        === INSERT OF 50 BYTE RECORDS ===
         Time for 100 write/read's for  SDBM_File                   0.12 seconds      12288 bytes
         Time for 100 write/read's for  MLDBM::Sync::SDBM_File      0.14 seconds      12288 bytes
         Time for 100 write/read's for  GDBM_File                   2.07 seconds      18066 bytes
         Time for 100 write/read's for  DB_File                     2.48 seconds      20480 bytes

        === INSERT OF 500 BYTE RECORDS ===
         Time for 100 write/read's for  SDBM_File                   0.21 seconds     658432 bytes
         Time for 100 write/read's for  MLDBM::Sync::SDBM_File      0.51 seconds     135168 bytes
         Time for 100 write/read's for  GDBM_File                   2.29 seconds      63472 bytes
         Time for 100 write/read's for  DB_File                     2.44 seconds     114688 bytes

        === INSERT OF 5000 BYTE RECORDS ===
        (skipping test for SDBM_File 1024 byte limit)
         Time for 100 write/read's for  MLDBM::Sync::SDBM_File      1.30 seconds    2101248 bytes
         Time for 100 write/read's for  GDBM_File                   2.55 seconds     832400 bytes
         Time for 100 write/read's for  DB_File                     3.27 seconds     839680 bytes

        === INSERT OF 20000 BYTE RECORDS ===
        (skipping test for SDBM_File 1024 byte limit)
         Time for 100 write/read's for  MLDBM::Sync::SDBM_File      4.54 seconds   13162496 bytes
         Time for 100 write/read's for  GDBM_File                   5.39 seconds    2063912 bytes
         Time for 100 write/read's for  DB_File                     4.79 seconds    2068480 bytes

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