| From: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Using indices for UNION. |
| Date: | 2014-01-14 09:10:40 |
| Message-ID: | 20140114.181040.107133006.horiguchi.kyotaro@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
This is cont'd from CF3.
http://www.postgresql.org/message-id/20131122.165927.27412386.horiguchi.kyotaro@lab.ntt.co.jp
The issue in brief is that UNION is never flattened differently
to UNION ALL so UNION cannot make use of index scan even if
usable.
This patch flattens UNION likewise currently did for UNION ALL.
This patch needs another 'UNION ALL' patch and further gain with
even another 'Widening application of indices' patch. ('Ready for
Commit' now in CF3..)
http://www.postgresql.org/message-id/20140114.180447.145186052.horiguchi.kyotaro@lab.ntt.co.jp
http://www.postgresql.org/message-id/20140114.180810.122352231.horiguchi.kyotaro@lab.ntt.co.jp
You can see the detailed outlines in the message at here,
http://www.postgresql.org/message-id/20131031.194251.12577697.horiguchi.kyotaro@lab.ntt.co.jp
The attached patche is rebased to current 9.4dev HEAD and make
check at the topmost directory and src/test/isolation are passed
without error.
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
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