On Tue, Jan 10, 2017 at 6:42 AM, Masahiko Sawada <sawada.m...@gmail.com> wrote: > Attached result of performance test with scale factor = 500 and the > test script I used. I measured each test at four times and plot > average of last three execution times to sf_500.png file. When table > has index, vacuum execution time is smallest when number of index and > parallel degree is same.
It does seem from those results that parallel heap scans aren't paying off, and in fact are hurting. It could be your I/O that's at odds with the parallel degree settings rather than the approach (ie: your I/O system can't handle that many parallel scans), but in any case it does warrant a few more tests. I'd suggest you try to: 1. Disable parallel lazy vacuum, leave parallel index scans 2. Limit parallel degree to number of indexes, leaving parallel lazy vacuum enabled 3. Cap lazy vacuum parallel degree by effective_io_concurrency, and index scan parallel degree to number of indexes And compare against your earlier test results. I suspect 1 could be the winner, but 3 has a chance too (if e_i_c is properly set up for your I/O system). -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
