[pgpool-general: 8393] Re: Query cache in shared memory bed performance

[Avi Raboah]

Hi,

Thanks for the fast response.

Do you think that if i’ll used memcached instead of shmem the performance
would be better?
Probably memcached using a better locking mechanism.

Thanks,

Avi.
On Tue, 13 Sep 2022 at 7:18 Tatsuo Ishii <ishii at sraoss.co.jp> wrote:

> > Hi,
> >
> > I ran 100 connections concurrently with pooling and query cache enabled,
> > and I saw a poor performance which indicting  on a very big query waits.
> >
> > I found in code that there is a locking mechanism when fetching from
> shmem.
> >
> > Could you please share why you make a critical section when pgpool trying
> > to read from cache?
>
> Because concurrent modifications to the tables could delete query
> cache, which will confuse process that are reading the cache.
>
> 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).
>
> 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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