On Wed, Feb 15, 2017 at 12:48 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> ... Maybe that difference matters to the memory prefetching >> controller, I dunno, but it seems funny that we did the PGXACT work to >> reduce the number of cache lines that had to be touched in order to >> take a snapshot to improve performance, and now we're talking about >> increasing it again, also to improve performance. > > Yes. I was skeptical that the original change was adequately proven > to be a good idea, and I'm even more skeptical this time. I think > every single number that's been reported about this is completely > machine-specific, and likely workload-specific too, and should not > be taken as a reason to do anything.
The original change definitely worked on read-only pgbench workloads on both x86 and Itanium, and the gains were pretty significant at higher client counts. I don't know whether we tested POWER. Read-only pgbench throughput is not the world, of course, but it's a reasonable proxy for high-concurrency, read-mostly workloads involving short transactions, so it's not nothing, either. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
