On Thu, Dec 10, 2015 at 11:36 AM, Andres Freund <and...@anarazel.de> wrote: >> In fact, having no way to get the relation length other than scanning >> 1000 files doesn't seem like an especially good choice even if we used >> a better data structure. Putting a header page in the heap would make >> getting the length of a relation O(1) instead of O(segments), and for >> a bonus, we'd be able to reliably detect it if a relation file >> disappeared out from under us. That's a difficult project and >> definitely not my top priority, but this code is old and crufty all >> the same.) > > The md layer doesn't really know whether it's dealing with an index, or > with an index, or ... So handling this via a metapage doesn't seem > particularly straightforward.
It's not straightforward, but I don't think that's the reason. What we could do is look at the call sites that use RelationGetNumberOfBlocks() and change some of them to get the information some other way instead. I believe get_relation_info() and initscan() are the primary culprits, accounting for some enormous percentage of the system calls we do on a read-only pgbench workload. Those functions certainly know enough to consult a metapage if we had such a thing. -- 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
