On 31.03.2011 21:23, Kevin Grittner wrote:
> Dan Ports<drkp@csail.mit.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 EnterpriseDB http://www.enterprisedb.com
