2011/9/14 Tom Lane <tgl@xxxxxxxxxxxxx> writes: > (...) I think that > the current state of affairs is still what depesz said, namely that > there might be cases where they'd be a win to use, except the lack of > WAL support is a killer. I imagine somebody will step up and do that > eventually. How much of work (in man days) do you estimate would this mean for someone who can program but has to learn PG internals first? Stefan 2011/9/14 Tom Lane <tgl@xxxxxxxxxxxxx>: > Peter Geoghegan <peter@xxxxxxxxxxxxxxx> writes: >> On 14 September 2011 00:04, Stefan Keller <sfkeller@xxxxxxxxx> wrote: >>> Has this been verified on a recent release? I can't believe that hash >>> performs so bad over all these points. Theory tells me otherwise and >>> http://en.wikipedia.org/wiki/Hash_table seems to be a success. > >> Hash indexes have been improved since 2005 - their performance was >> improved quite a bit in 9.0. Here's a more recent analysis: > >> http://www.depesz.com/index.php/2010/06/28/should-you-use-hash-index/ > > Yeah, looking into the git logs shows several separate major changes > committed during 2008, including storing only the hash code not the > whole indexed value (big win on wide values, and lets you index values > larger than one index page, which doesn't work in btree). I think that > the current state of affairs is still what depesz said, namely that > there might be cases where they'd be a win to use, except the lack of > WAL support is a killer. I imagine somebody will step up and do that > eventually. > > The big picture though is that we're not going to remove hash indexes, > even if they're nearly useless in themselves, because hash index > opclasses provide the foundation for the system's knowledge of how to > do the datatype-specific hashing needed for hash joins and hash > aggregation. And those things *are* big wins, even if hash indexes > themselves never become so. > > regards, tom lane > -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
