Re: PostgreSQL 8.0 occasionally slow down

2007/6/29, Richard Huxton <dev(at)archonet(dot)com>:
>
> Ho Fat Tsang wrote:
> > Hi Richard,
> >
> > I've tested again according your suggestion. I noticed that for each
> > time the pgsql slow down, there is a short period a process called
> > "pdflush"
> > eating up lot of I/O. I've goolgled and know it is a process for writing
> > dirty pages back to the disk by the Linux kernel. I will have further
> > investigation on this process with my limited knowledge on Linux kernel.
>
> Well, pdflush is responsible for flushing dirty pages to disk on behalf
> of all processes.
>
> If it's doing it every 3 minutes while checkpoints are happening every
> 30 seconds then I don't see how it's PG that's responsible.
>
> There are three possibilities:
> 1. PG isn't actually checkpointing every 30 seconds.
> 2. There is a burst of query activity every 3 minutes that causes a lot
> of writing.
> 3. Some other process is responsible.

Exactly ! you are right, finally i have found that the root cause for this
is the application that use PG. There is memory leak using MappedByteBuffer
(writing in java), it leads high I/O loading and finally reaches the ratio
that pdflush is being kicked start in the kernel.

Thank you for helping a lot in digging out this issue ! learn much for you
guys !

> Correct me if i am wrong. It seems postgresql 8.0 does not bundle
> > auto-vacuum by default. So all vacuum and analyse are done manually ? So
> > what i have tested related to vaccuum is running auto-vacuum (a
> executeable
> > located in /bin) parallel under normal production load but it seems
> won't
> > help.
>
> Can't remember whether 8.0 had autovacuum bundled and turned off or not
> bundled at all. If it's not running it can't be causing this problem
> though.
>
> --
> Richard Huxton
> Archonet Ltd
>