Hi, I recently have seen some perf profiles in which _mdfd_getseg() was in the top #3 when VACUUMing large (~200GB) relations. Called by mdread(), mdwrite(). Looking at it's implementation, I am not surprised. It iterates over all segment entries a relations has; for every read or write. That's not painful for smaller relations, but at a couple of hundred GB it starts to be annoying. Especially if kernel readahead has already read in all data from disk.
I don't have a good idea what to do about this yet, but it seems like something that should be fixed mid-term. The best I can come up is is caching the last mdvec used, but that's fairly ugly. Alternatively it might be a good idea to not store MdfdVec as a linked list, but as a densely allocated array. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
