On 10.9.2014 20:31, Robert Haas wrote: > On Wed, Sep 10, 2014 at 2:25 PM, Heikki Linnakangas > <hlinnakan...@vmware.com> wrote: >> The dense-alloc-v5.patch looks good to me. I have committed that with minor >> cleanup (more comments below). I have not looked at the second patch. > > Gah. I was in the middle of doing this. Sigh. > >>> * the chunks size is 32kB (instead of 16kB), and we're using 1/4 >>> threshold for 'oversized' items >>> >>> We need the threshold to be >=8kB, to trigger the special case >>> within AllocSet. The 1/4 rule is consistent with ALLOC_CHUNK_FRACTION. >> >> Should we care about the fact that if there are only a few tuples, we will >> nevertheless waste 32kB of memory for the chunk? I guess not, but I thought >> I'd mention it. The smallest allowed value for work_mem is 64kB. > > I think we should change the threshold here to 1/8th. The worst case > memory wastage as-is ~32k/5 > 6k.
So you'd lower the threshold to 4kB? That may lower the wastage in the chunks, but palloc will actually allocate 8kB anyway, wasting up to additional 4kB. So I don't see how lowering the threshold to 1/8th improves the situation ... Tomas -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
