At 01:05 AM 22/11/2002 +1100, Philip Warner wrote:
I have confirmed that I get the same strategy as you on an empty DB; I
think you should run an ANALYZE then try the query again. We run an
analyze every night.
I should point out that as of recent versions of PG (7.1?), ANALYZE is a
lot cheaper than it used to be: current implementations take a random
sampling of data from each table file -- they no longer scan the entire
database.
It samples a statistically relevant proportion of the data to build a
profile, which the planner/optimizer then uses. Without running it, you
will definitely see odd behaviour, most likely based on a near empty database.
The optimizer output from your earlier queries seems to indicate that it
thinks the messageblks table has 1453 rows. If the database is really 5GB,
then I think it is planning based on very old analysis.
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