On 4/21/05, Bruce Momjian <pgman@candle.pha.pa.us> wrote: > > I believe Tom is completing this TODO item: > > * Allow non-bitmap indexes to be combined by creating bitmaps in memory >
Thanks Bruce. That definitely answers my first question about lossy index types. Sorry for asking a TODO answered question. [MENTAL NOTE: Check TODOs as well as archives...] I'm still curious about the implications of this (my) assumption: > > It will also keep long lists of ORs from turning what would have been > > a >10% index scan into a seq scan, yes? I suppose there is some > > balance that needs to be calculated on > > number-of-conditions-per-index-scan vs startup-cost-of-X-index-scans. > > E.g., if you have table with 10M rows and an IN clause with 500 > > elements, it might be better to start 20 index scans with 25 condition > > each instead of a single big index scan (what we do now if the cost > > isn't too high), 500 index scans (what a simple "spin off a scan per > > condition" algo would do, and what it _looks_ like the new code did to > > your test query...), or a seq scan. > > Though I'm not sure if I was completely clear there... And just to be clear, unless I'm just misunderstanding the TODO, it looks like this: > > unrelated indexes? Could this bitmapping code be used to combine > > indexes from different tables, say in a large UNION or inherited table > > setup? should be true when the implementation is complete. The reason I ask about the inherited table index bitmapping is that it might provide a way to check for cross-partition UNIQUE constraints. Perhaps something like: ALTER TABLE base_table ADD CONSTRAINT col_global_uniq_constraint GLOBALLY UNIQUE (unique_column); That could use a bitmapped OR scan of indexes on "unique_column" on the base table and all descendant tables to check for a unique value across a "partitioned table". Hmmm... thinking more, I suppose it could just to a quick scan of each index in order, so that might not be useful. -- Mike Rylander [EMAIL PROTECTED] GPLS -- PINES Development Database Developer http://open-ils.org ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
