pgsql: Fix bugs in indexing of in-doubt HOT-updated tuples.

Fix bugs in indexing of in-doubt HOT-updated tuples.

If we find a DELETE_IN_PROGRESS HOT-updated tuple, it is impossible to know
whether to index it or not except by waiting to see if the deleting
transaction commits. If it doesn't, the tuple might again be LIVE, meaning
we have to index it. So wait and recheck in that case.

Also, we must not rely on ii_BrokenHotChain to decide that it's possible to
omit tuples from the index. That could result in omitting tuples that we
need, particularly in view of yesterday's fixes to not necessarily set
indcheckxmin (but it's broken even without that, as per my analysis today).
Since this is just an extremely marginal performance optimization, dropping
the test shouldn't hurt.

These cases are only expected to happen in system catalogs (they're
possible there due to early release of RowExclusiveLock in most
catalog-update code paths). Since reindexing of a system catalog isn't a
particularly performance-critical operation anyway, there's no real need to
be concerned about possible performance degradation from these changes.

The worst aspects of this bug were introduced in 9.0 --- 8.x will always
wait out a DELETE_IN_PROGRESS tuple. But I think dropping index entries
on the strength of ii_BrokenHotChain is dangerous even without that, so
back-patch removal of that optimization to 8.3 and 8.4.

Branch
------
REL8_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/3c34d7ee8e4617efd3d18999a4453f76bce93f55

Modified Files
--------------
src/backend/catalog/index.c | 61 +++++++++++++++++++++++-------------------
1 files changed, 33 insertions(+), 28 deletions(-)