Re: performance "tests"

Naomi Walker wrote:
>  From my many years of Informix knowledge, we noticed that checkpoints,
> during high activity times, did take a long time, because it locked the
> shared memory segment.  We found that setting the checkpoint knobs to flush
> almost constantly, overall, was much better for performance.
>
> Looking in postgresql.conf, it seems that some tweaking of :
> CHECKPOINT_SEGMENTS and CHECKPOINT_TIMEOUT are in order.
>
> I also see some interesting items in the WAL_* configuration parameters,
> and would look at these as well.  Again, in Informix-speak, we were able to
> control when the buffers flushed to disk, with parameters like:
>                          Start flushing buffers when they are X% full
>                             and keep flushing until they are X% full
>
> Overall, having TONS of buffers helped benchmark performance, but could
> have slowed down checkpoints had we not continually flushed to disk.

Actually, we don't lock shared memory like Informix does.  As I
remember, other backends can write to the WAL while we are doing the
checkpoint.  In fact, there is code in there that expects the WAL file
may grow during checkpointing.

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