Thanks a lot for your help.
On 10/17/06, Dawid Kuroczko <qnex42(at)gmail(dot)com> wrote:
> On 10/17/06, soni de <soni(dot)de(at)gmail(dot)com> wrote:
> > I didn't understand the "Bitmap Scan" and the sentence "indexes will be
> > dynamically converted to bitmaps in memory". What does mean by "Bitmap Scan"
> > in database?
> > Can anybody help us regarding above query?
> Assume you have a table:
> CREATE TABLE foo (
> some_key int,
> some_time timestamp with time zone,
> some_data text
> And two indexes:
> CREATE INDEX foo_key ON foo (some_key);
> CREATE INDEX foo_time ON foo (some_time);
> Now, you make a query:
> SELECT * from foo WHERE some_key > 10 AND some_time >
> ...originally planner would choose only one index to use -- and would use
> one which it think its best.
> The 8.1 version does differently: It will scan foo_key index -- make a
> bitmap out of it,
> scan foo_time index -- make another bitmap out of it, binary AND these
> and will read the data from the table using such combined bitmap. It
> could as well
> use "OR" if you used OR in your query.
> Hence -- it can be faster, especially for large tables and selective
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