[pgpool-hackers: 4195] Re: [pgpool-general: 8406] Re: Query cache in shared memory bed performance

[Tatsuo Ishii]

Hi Pgpool-II developers,

>> Ideally the process reading query cache should only grab a shared
>> lock, which will not block other reading process. Unfortunately we do
>> not have shared lock facility (we only have exclusive lock).
> 
> I have created a proof of concept patch to implement the share lock
> using flock(2). Attached is a graph showing the benchmark result. The
> Y axis is the number of queries executed within 1 second. The X axis
> is the number of concurrent session.
> 
> As you can see new implementation (enable query cache (flock,
> exclusive lock for update), green line) outperforms existing
> implementation using exclusive lock only (red line) as number of
> concurrent users increases. Note that this is somewhat extreme case
> because the cache hit ratio is 100% (i.e. exactly same query is used
> during the benchmark). So the difference will not be that big in the
> wild.
> 
> The actual query used was:
> SELECT repeat('abcdefg', 500);
> 
> The blue line is the case when query cache is disabled just for
> reference.
> 
> The benchmark was performed on a Ubuntu 20 box with 16GB mem, 6 physical
> cores, 12 vcores.

Attached is the v1 of the patch. The difference from the patch posted
at pgpool-general is, adding on_proc_exit so that the lock file is
unlinked upon the pgpool main process exits. If there's no objection,
I will add this to the master branch.

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp
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