[Koha-bugs] [Bug 7879] New: Memoize::Memcached two times slower than it should be

[bugzilla-daemon at bugs.koha-community.org]

http://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=7879

          Priority: P5 - low
 Change sponsored?: ---
            Bug ID: 7879
          Assignee: gmcharlt at gmail.com
           Summary: Memoize::Memcached two times slower than it should be
        QA Contact: koha.sekjal at gmail.com
          Severity: enhancement
    Classification: Unclassified
                OS: All
          Reporter: dpavlin at rot13.org
          Hardware: All
            Status: NEW
           Version: rel_3_6
         Component: Architecture, internals, and plumbing
           Product: Koha

Created attachment 8791
  -->
http://bugs.koha-community.org/bugzilla3/attachment.cgi?id=8791&action=edit
Memoize::Memcached 2x speedup

While profiling Koha with memcached turned on I was stunned by NYTProf results:

Calls     P     F     Exclus  Inclus  Subroutine
55    2    1    1.70s    1.70s    Memoize::Memcached::EXISTS
55    2    1    1.68s    1.68s    Memoize::Memcached::FETCH

Code analysts showed that it generates two FETCH requests for each item.

Attached patch fixes upstream module and might be beneficial on existing Koha
installations which use memcached.

It uses shared variable, and it's safe in CGI installations.

Having shared variable showed another characteristic of current code: 

55    2    1    33.8ms    33.8ms    Memoize::Memcached::EXISTS
55    2    1    362µs    362µs    Memoize::Memcached::FETCH

This is good, but a little bit too fast. Examining hit and miss ratio stored in
Koha::Persistant::stats it turns out that we are accessing memcache 106 times,
but only 4 times for new values.

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