>>> It really has very little impact. It only affects index scans, and
>>> even then only if effective_cache_size is less than the size of the
>> table.
>>>
>>> Essentially, when this kicks in, it models the effect that if you are
>>> index scanning a table much larger than the size of your cache, you
>>> might have to reread some blocks that you previously read in during
>>> *that same index scan*.
>>
>> Ok, thanks for clearing that up for me. Still, I think the doc could be
>> improved on this point (sorry to be a bit obsessed with that, but I'm one
>> of
>> the french translators, so I like the doc to be perfect :) )
>
>Yes, I agree. I was confused for quite a long time, too, until I read
>the code. I think many people think this value is much more important
>than it really is.
>
>(That having been said, I have no current plans to write such a doc
>patch myself.)
>
>...Robert
How about adding a comment to the wiki performance page....
http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server