> rel->pages = RelationGetNumberOfBlocks(relation);
Is RelationGetNumberOfBlocks cheap enough that you can easily use it for the
optimizer ?
I myself have always preferred more stable estimates that only change
when told to. I never liked that vacuum (without analyze) and create index
change those values, imho only analyze should. But I am used to applications
that prepare a query and hold the plan for days or weeks. If you happen to
create the plan when the table is by chance empty you lost.
But it seems I am quite alone with that opinion.
> A variant of this is to set reltuples = density, relpages = 1 instead
> of 0, which makes the relpages value a lie but would be even less likely
> to confuse client-side code.
I would let analyze still fill in the correct values.
The 0 or 1 page previous denstity could be used for only when the table is empty.
I don't think eighter would confuse client-side code more or less.
More confusing for client-side code would be if the two would not show the
analyze results any more.
I would like to see this configurable. Like "use_analyzed_stats" or
"enable_online_statistics" or some such that can be used more future
online statistics.
One setting would use:
pages = RelationGetNumberOfBlocks(relation)
count = pages * reltuples / relpages
the other:
pages = relpages
count = relcount
Andreas
