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Re: Terrible Write Performance of a Stored Procedure

From: Scott Mead <scott(dot)lists(at)enterprisedb(dot)com>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: Brian Troutwine <goofyheadedpunk(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Terrible Write Performance of a Stored Procedure
Date: 2009-06-29 12:54:40
Message-ID: d3ab2ec80906290554j564dcdew7f992407df34882e@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-performance
>
> You're right that it should be removed, but this explanation is wrong. The
> behavior as configured is actually "if there are >=100 other transactions in
> progress, wait 0.1 second before committing after the first one gets
> committed", in hopes that one of the other 100 might also join along in the
> disk write.


  Thanks for the correction.  My question is how you're getting .1 seconds
from his commit_delay?

if (CommitDelay > 0 && enableFsync &&
    CountActiveBackends() >= CommitSiblings)
         pg_usleep(CommitDelay);

  Wouldn't this actually be 1 second based on a commit_delay of 100000?



>
>
> Since in this case max_connections it set to 100, it's actually impossible
> for the commit_delay/commit_siblings behavior to trigger give this
> configuration.  That's one reason it should be removed.  The other is that i
> general, if you don't exactly what you're doing, you shouldn't be touching
> either parameters; they don't do what people expect them to and it's
> extremely unlikely you'll encounter any of the rare use cases where they
> might help.


   After looking, I agree, thanks again for the correction Greg.

--Scott

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