Re: update query taking too long

Chris wrote (in part):

> I didn't have logging set up before but it's up and running now and I
> was getting
>
> LOG: checkpoints are occurring too frequently (26 seconds apart)
> HINT: Consider increasing the configuration parameter
> "checkpoint_segments".
>
> So I increased that from 10 to 30 and it finished:
>
> UPDATE 3500101
> Time: 146513.349 ms
>
I have not used postgreSQL since I tried it once in about 1998 (when I found
it unsatisfactory, but much has changed since then), but I am going to try
it again. What would be a good checkpointing interval? I would guess 26
seconds is too often. What considerations go into picking a checkpointing
interval?

I note, from the book "PostgreSQL" second edition by Douglas and Doublas,
the following parameters are available:

WAL_BUFFERS The default is 8.
CHECKPOINT_SEGMENTS The default is 3. This would have been too low for the
O.P. Would it make sense to start with a higher value
or is this a good value and just not appropriate for
the O.P.? Should CHECKPOINT_SEGMENTS be raised until
the checkpointing is about half CHECKPOINT_TIMEOUT,
e.g., 150 seconds while the dbms is running typical
work?
CHECKPOINT_TIMEOUT The default is 300 seconds.
CHECKPOINT_WARNING The default is 30 seconds.

My machine has 8 GBytes RAM and it worked perfectly well (very very little
paging) when it had 4 GBytes RAM. I doubled it because it was cheap at the
time and I was afraid it would become unavailable later. It is usually
between 2/3 and 3/4 used by the cache. When I run IBM DB2 on it, the choke
point is the IO time spent writing the logfiles.

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