Even though Ijust proposed it, now I think that the idea of having postgres automatically gather statistics only when an estimate is grossly wrong is not a good one. This will just obscure the need to run analyze, and many people will then always be using moderately bad statistics without realizing it.2. Instability of plans. Right now, the planner will not change plans underneath you --- you have to issue an explicit VACUUM or ANALYZE to change the terms of discussion. That would stop being true if physical file size were always taken into account. Maybe this is a problem, or maybe it isn't ... as someone who likes to be able to debug planner behavior without actually creating umpteen-gig test tables, my world view may be a bit skewed ...
It's certainly doable if we decide the pluses outweigh the minuses. Thoughts?
(I think I used postgres in a production environment for about six months without even knowing about the ANALYZE command--with small data sets it's not obvious--and it was still blazingly fast compared to foxpro.)
If pgautovacuum does ANALYZE and we can get most people to use pgautovacuum, I think this problem will go away.
Another possibility is simply to make postgres generate a warning, saying:
WARNING: statistics for table xxxxxx are off by a factor of y. You should ANALYZE this table.
Paul
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