oops dam spell checker really should be rarely sorry
Justin wrote:
Then why are the estimates so far off??? If estimates where correct
would it improve the performance that much.
Vaccum is set to run automatically so the stats stay update.
Total record count for the tables for all the tables put together is
around 120,000 the query returns only 458 records which is correct.
If i am correct in my understanding the reason the index improved the
query so much is the wooper table gets hit hard because it appears in
3 separate nested queries . So taking only 458 records returned from
the parent query times 3 for 1,375 table scans going through 21,873
records for a total number records being processed to 30,075,375 on a
table with no index. So if you look at it that way PostgreSql did
remarkably well processing the query in 18 to 20 seconds.
The idea behind adhoc indexes is when one shot queries or rarely used
queries are created that would require numerous indexes to run in a
decent time can be run in a faction of the time. This also saves
processing times across the entire system where creating indexes for
the all the possible queries is impractical
This does not take away the need for index but speed up ad-hoc
queries created from a website or other business analysis tool that
someone might create
Tom Lane wrote:
Justin <[EMAIL PROTECTED]> writes:
The idea of ad hoc indexes is speed up loop scans To prove my idea i
created a sql file in PGAdmin that creates the indexes on the fly then
runs the query then drops the indexs.
without the indexes it takes 18 to 19 seconds to run the query.
To create the index and do the query takes 400 milliseconds.
The example you show doesn't convince me of much of anything, because
the estimated rowcounts are so far off. I think you're basically
dealing with an estimation failure and it's pure luck that the extra
index fixes it.
regards, tom lane
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