On Thu, Jul 20, 2017 at 12:51 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Robert Haas <robertmh...@gmail.com> writes: > > I think that's a valid point. There are also other concerns here - > > e.g. whether instead of adopting the patch as proposed we ought to (a) > > use some smaller size, or (b) keep the size as-is but reduce the > > maximum fraction of shared_buffers that can be consumed, or (c) divide > > the ring buffer size through by autovacuum_max_workers. Personally, > > of those approaches, I favor (b). I think a 16MB ring buffer is > > probably just fine if you've got 8GB of shared_buffers but I'm > > skeptical about it when you've got 128MB of shared_buffers. > > WFM. I agree with *not* dividing the basic ring buffer size by > autovacuum_max_workers. If you have allocated more AV workers, I think > you expect AV to go faster, not for the workers to start fighting among > themselves. > But fighting among themselves is just what they do regarding the autovacuum_vacuum_cost_limit, so I don't see why it should be one way there but different here. The reason for setting autovacuum_max_workers to N is so that small tables aren't completely starved of vacuuming even if N-1 larger tables are already being vacuumed simultaneously. Now the small tables get vacuumed at speed 1/N, which kind of sucks, but that is the mechanism we currently have. Of course just because we are in a hole with vacuum_cost_limit doesn't mean we should dig ourselves deeper, but we are being inconsistent then. Cheers, Jeff
