Re: SSI bug?

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Dan Ports <drkp(at)csail(dot)mit(dot)edu>, YAMAMOTO Takashi <yamt(at)mwd(dot)biglobe(dot)ne(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: SSI bug?
Date: 2011-03-31 18:31:37
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On 31.03.2011 21:23, Kevin Grittner wrote:
> Dan Ports<drkp(at)csail(dot)mit(dot)edu> wrote:
>> On Thu, Mar 31, 2011 at 11:06:30AM -0500, Kevin Grittner wrote:
>>> The only thing I've been on the fence about is whether it
>>> makes more sense to allocate it all up front or to continue to
> allow
>>> incremental allocation but set a hard limit on the number of
> entries
>>> allocated for each shared memory HTAB. Is there a performance-
>>> related reason to choose one path or the other?
>> Seems like it would be marginally better to allocate it up front --
> then
>> you don't have the cost of having to split buckets later as it
> grows.
> The attached patch should cover that.

That's not enough. The hash tables can grow beyond the maximum size you
specify in ShmemInitHash. It's just a hint to size the directory within
the hash table.

We'll need to teach dynahash not to allocate any more entries after the
preallocation. A new HASH_NO_GROW flag to hash_create() seems like a
suitable interface.

Heikki Linnakangas

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