On 2016-02-22 20:44:35 +0100, Fabien COELHO wrote: > > >>Random updates on 16 tables which total to 1.1GB of data, so this is in > >>buffer, no significant "read" traffic. > >> > >>(1) with 16 tablespaces (1 per table) on 1 disk : 680.0 tps > >> per second avg, stddev [ min q1 median d3 max ] <=300tps > >> 679.6 ± 750.4 [0.0, 317.0, 371.0, 438.5, 2724.0] 19.5% > >> > >>(2) with 1 tablespace on 1 disk : 956.0 tps > >> per second avg, stddev [ min q1 median d3 max ] <=300tps > >> 956.2 ± 796.5 [3.0, 488.0, 583.0, 742.0, 2774.0] 2.1% > > > >Interesting. That doesn't reflect my own tests, even on rotating media, > >at all. I wonder if it's related to: > >https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=23d0127096cb91cb6d354bdc71bd88a7bae3a1d5 > > > >If you use your 12.04 kernel, that'd not be fixed. Which might be a > >reason to do it as you suggest. > > > >Could you share the exact details of that workload? > > See attached scripts (sh to create the 16 tables in the default or 16 table > spaces, small sql bench script, stat computation script). > > The per-second stats were computed with: > > grep progress: pgbench.out | cut -d' ' -f4 | avg.py --length=1000 > --limit=300 > > Host is 8 cpu 16 GB, 2 HDD in RAID 1.
Well, that's not a particularly meaningful workload. You increased the number of flushed to the same number of disks considerably. For a meaningful comparison you'd have to compare using one writeback context for N tablespaces on N separate disks/raids, and using N writeback contexts for the same. Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers