[Koha-bugs] [Bug 17833] New: Memcached silently fails to _initilize_memcached() on the second time it is invoked

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

https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=17833

            Bug ID: 17833
           Summary: Memcached silently fails to _initilize_memcached() on
                    the second time it is invoked
 Change sponsored?: ---
           Product: Koha
           Version: master
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P5 - low
         Component: Architecture, internals, and plumbing
          Assignee: gmcharlt at gmail.com
          Reporter: olli-antti.kivilahti at jns.fi
        QA Contact: testopia at bugs.koha-community.org

When _initilize_memcached() is called the first time, it sets the
'ismemcached'-key and returns 1.

When _initilize_memcached() is called the second time, the 'ismemcached'-key
already exists and '' is returned (this default to False in Perl).
Koha thinks that memcached is not in use and decides to use some other caching
mechanism instead.

Cache::Memcached::Fast returns undef on server error:
https://metacpan.org/pod/Cache::Memcached::Fast#add

Koha MUST listen to undefined, instead of False to define whether or not
memcached is properly working.


Also added simple helpful diagnostics to help identify and log when this
memcached server connection problem arises.


Here is a small test run to verify this behaviour:
root at kohadev:~# echo "fresh memcached start"
fresh memcached start
root at kohadev:~# perl l.pl
127.0.0.1:4545 1.4.14 (Ubuntu)
def  : '1'
getkey: 'text'
root at kohadev:~# echo "val already cached"
val already cached
root at kohadev:~# perl l.pl
127.0.0.1:4545 1.4.14 (Ubuntu)
def  : ''
getkey: 'text'
root at kohadev:~# echo "memcached killed and not responding"
memcached killed and not responding
root at kohadev:~# perl l.pl
undef
getkey: ''
root at kohadev:~# echo "The return value is undefined"
The return value is undefined
root at kohadev:~#



Here is the code snippet used to test the Memcached-server in the previous
example output:

kivilahtio at koha_ci_1 /h/k/Koha> cat t.pl
use Cache::Memcached::Fast;
use Modern::Perl;

my $memd = new Cache::Memcached::Fast({
    servers => [ '/lxcBindMount/tmp/memcached.sock' ],
    namespace => 'koha_ci_1:',
    connect_timeout => 0.2,
    io_timeout => 0.5,
    close_on_error => 1,
    max_failures => 3,
    failure_timeout => 2,
    ketama_points => 150,
    nowait => 1,
    hash_namespace => 1,
});


# Get server versions.
my $versions = $memd->server_versions;
while (my ($server, $version) = each %$versions) {
    print "$server $version\n";
}

# Store scalars.
my $rv = $memd->add('skey', 'text');
print "undef\n" if not defined $rv;
print "def  : '$rv'\n" if defined $rv;
print "getkey: '".$memd->get('skey')."'\n";

-- 
You are receiving this mail because:
You are watching all bug changes.