Re: Improvement of checkpoint IO scheduler for stable transaction responses

On 2013-06-16 17:27:56 +0300, Heikki Linnakangas wrote:

> A long time ago, Itagaki wrote a patch to sort the checkpoint writes: www.postgresql.org/message-id/flat/20070614153758.6A62.ITAGAKI.TAKAHIRO@oss.ntt.co.jp.
> He posted very promising performance numbers, but it was dropped because Tom
> couldn't reproduce the numbers, and because sorting requires allocating a
> large array, which has the risk of running out of memory, which would be bad
> when you're trying to checkpoint.

Hm. We could allocate the array early on since the number of buffers
doesn't change. Sure that would be pessimistic, but that seems fine.

Alternatively I can very well imagine that it would still be beneficial
to sort the dirty buffers in shared buffers. I.e. scan till we found 50k
dirty pages, sort them and only then write them out.