On Wed, Jul 12, 2017 at 1:10 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: >>> Yes, I also think the same idea can be used, in fact, I have mentioned >>> it [1] as soon as you have committed that patch. Do we want to do >>> anything at this stage for PG-10? I don't think we should attempt >>> something this late unless people feel this is a show-stopper issue >>> for usage of hash indexes. If required, I think a separate function >>> can be provided to allow users to perform squeeze operation. >> >> Sorry, I have no idea how critical this squeeze thing is for the >> newfangled hash indexes, so I cannot comment on that. Does this make >> the indexes unusable in some way under some circumstances? > > It seems so. Basically, in the case of a large number of duplicates, > we hit the maximum number of overflow pages. There is a theoretical > possibility of hitting it but it could also happen that we are not > free the existing unused overflow pages due to which it keeps on > growing and hit the limit. I have requested up thread to verify if > that is happening in this case and I am still waiting for same. The > squeeze operation does free such unused overflow pages after cleaning > them. As this is a costly operation and needs a cleanup lock, so we > currently perform it only during Vacuum and next split from the bucket > which can have redundant overflow pages.
Oops. It was rather short-sighted of us not to increase HASH_MAX_BITMAPS when we bumped HASH_VERSION. Actually removing that limit is hard, but we could have easily bumped it for 128 to say 1024 without (I think) causing any problem, which would have given us quite a bit of headroom here. I suppose we could still try to jam that change in before beta3 (bumping HASH_VERSION again) but that might be asking for trouble. -- 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
