We currently execute a lot of joins as Nested Loops which would be more efficient if we could batch together all the outer keys and execute a single inner bitmap index scan for all of them together.
Essentially what I'm saying is that we're missing a trick with Hash Joins which currently require that we can execute the inner side once without any parameters from the outer side. Instead what we could do is build up the hash table, then scan the hash table building up an array of keys and pass them as a parameter to the inner side. The inner side could do a bitmap index scan to fetch them all at once and start returning them just as normal to the hash join. There are a couple details: 1) Batched hash joins. Actually I think this would be fairly straightforward. You want to rescan the inner side once for each batch. That would actually be easier than what we currently do with saving tuples to files and all that. 2) How to pass the keys. This could be a bit tricky especially for multi-column keys. My first thought was to build up an actually Array node but that only really works for single-column keys I think. Besides it would be more efficient to somehow arrange to pass over a reference to the whole hash. I fear the real complexity would be (as always) in the planner rather than the executor. I haven't really looked into what it would take to arrange this or how to decide when to do it. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's RemoteDBA services! ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
