On Sun, Aug 25, 2013 at 10:11:50PM -0400, Tom Lane wrote:
Michael Paquier <michael.paquier@gmail.com> writes:
On Thu, Aug 22, 2013 at 11:55 PM, Blake Smith wrote:
The combined entry is used to support "contains (@>)" queries, and the key
only item is used to support "key contains (?)" queries. This change seems
to help especially with hstore keys that have high cardinalities. Downsides
of this change is that it requires an index rebuild, and the index will be
larger in size.
Index rebuild would be a problem only for minor releases,
That's completely false; people have expected major releases to be
on-disk-compatible for several years now. While there probably will be
future releases in which we are willing to break storage compatibility,
a contrib module doesn't get to dictate that.

What might be a practical solution, especially if this isn't always a
win (which seems likely given the index-bloat risk), is to make hstore
offer two different GIN index opclasses, one that works the traditional
way and one that works this way.

Another thing that needs to be taken into account here is Oleg and
Teodor's in-progress work on extending hstore:
https://www.pgcon.org/2013/schedule/events/518.en.html
I'm not sure if this patch would conflict with that at all, but it
needs to be considered.
We can disallow in-place upgrades for clusters that use certain contrib
modules --- we have done that in the past.

--
   Bruce Momjian <bruce@momjian.us> http://momjian.us
   EnterpriseDB http://enterprisedb.com

   + It's impossible for everything to be true. +

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