Re: Hash indexes and effective_cache_size in CREATE INDEX documentation

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Geoghegan <pg(at)heroku(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hash indexes and effective_cache_size in CREATE INDEX documentation
Date: 2016-07-31 17:05:56
Message-ID: 32276.1469984756@sss.pgh.pa.us
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I wrote:
> Peter Geoghegan <pg(at)heroku(dot)com> writes:
>> The CREATE INDEX documentation states:
>> "For hash indexes, the value of effective_cache_size is also relevant
>> to index creation time: PostgreSQL will use one of two different hash
>> index creation methods depending on whether the estimated index size
>> is more or less than effective_cache_size.

> Oooh. That should've been changed by 4adc2f72, and then again in
> 9563d5b5. Will fix.

After looking at that a bit, I'm strongly tempted to just take out
the last two sentences of the para, reducing it to the advice concerning
maintenance_work_mem. That seems sufficient to describe the current
behavior, and given our awful track record about maintaining this
documentation, I'm not sure that going into more detail is really
a good idea. Comments?

regards, tom lane

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