Hello Horiguchi-san,
On 09/17/2015 12:45 PM, Kyotaro HORIGUCHI wrote:
After all, what should be done to properly ignore useless
conditions would be,
1. Make create_index_paths() to make the list of restrict
clauses which are implied by the index predicate of the index
in focus. The list would be stored as a member in
IndexOptInfo. Then create index clauses excluding the listed
clauses and call get_index_paths using them. Modify
check_index_only() to ignore the listed clauses when pulling
varattnos. This is similar but different a bit to what I said
in the previous mail.
2. Pass the listed clauses to generated IndexPath.
3. Modify extract_nonindex_conditions to be called with the
exclusion list and the cluases are exluded from the result of
the function.
4. Make create_indexscan_plan to extract qpqual excluding the
exclusion list.
The same result could be obtained by more smarter way but the
steps above will archive right decision on whether to do index
only scan on partial index and correct cost estimate propery
ignoring unused restrictions.
Does this make sense for you?
Yes, this seems sane. I've been poking at this a bit too, and I came to
the same plan in general, except that I think it's better to build list
of clauses that are *not* implied by the index, because that's what we
need both in cost_index and check_index_only.
It also seems to me that this change (arguably a bug fix) should pretty
much make the original patch irrelevant, because check_index_only can
simply walk over the new list.
regards
--
Tomas Vondra http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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