Jeff Larsen wrote:
If it's possible to consider this abstractly, is there any particular
reason why there is such a vast difference in performance? I would
guess that is has something to do with how the WHERE conditions are
applied to a view composed of a UNION of queries. Perhaps this is an
opportunity for improvement in the code. In the first case, it's as if
the server is doing the union on all rows (over 10 million altogether
in my case) without filtering, then applying the conditions to the
result. Maybe there is no better way.
I can post query plans if anyone is interested. I haven't really
learned how to make sense out of them myself yet.
For my purposes, I'm content to use the union of separate views in my
application, so if this doesn't pique anyone's interest, feel free to
ignore it.
I hit this as well in less impacting statements. I found myself curious
that the sub-plan would have to be executed in full before it applied
the filter. Perhaps PostgreSQL has difficulty pushing WHERE conditions
through the rule system? It's an area I only barely understand, so I
never looked further...
I'm interested, but do not have anything of value to provide either. :-)
Cheers,
mark
--
Mark Mielke <mark@xxxxxxxxx>
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TIP 6: explain analyze is your friend
