Re: explanation of some configs

On Sat, 2009-02-07 at 01:52 +0100, Thomas Finneid wrote:
> Hi
>
> I am having some problem understanding the details of a couple of
> configuration directives. Here is what I think I understand it so far:
>
> effective_cache_size
> - specifies in how many B/KB/MB will be used to cache data
> between pg and the OS?
> - what is actually cached and how it is actually used by the
> planner and how does it affect the planner and the queries?
> -in other words, when and why do I need to set this parameter?

This is just a hint to tell the planner how much cache will generally be
available. The number should be reflective of your shared buffers +
available operating system cache. If you database is postgresql only you
can generally set this very high 75% of available ram. If not then you
need to tone it down.

>
> checkpoint_segments
> - specifies the number of segments?

The number of segments that will be used before a checkpoint is forced.

> size: number*16MB?

Yes but they are not preallocated.

> - means when number of WAL segments has filled up and matches
> checkpoint segment, dirty data is written to disk?

A checkpoint occurs.

Joshua D. Drake

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