| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Petr Jelinek <petr(at)2ndquadrant(dot)com> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Tobias Florek <postgres(at)ibotty(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Subject: | Re: [NOVICE] WHERE clause not used when index is used |
| Date: | 2016-03-01 18:47:05 |
| Message-ID: | 19581.1456858025@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers pgsql-novice |
I wrote:
> I'm not sure if the costing change is a bug or not --- the non-bitmap scan
> does seem to be cheaper in reality, but not by a couple orders of
> magnitude as the planner now thinks.
Ah, scratch that, I wasn't looking closely enough. The 9.4 plan is an
IndexScan whereas 9.5+ uses IndexOnlyScan, which accounts for the cost
differential. The reason it changed is the remove_unused_subquery_outputs
patch (55d5b3c08279b487), which allows the subquery to know that it
doesn't actually have to return all columns of tenk1, so that an
index-only scan is legal.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Robert Haas | 2016-03-01 18:54:46 | Re: psql completion for ids in multibyte string |
| Previous Message | Robert Haas | 2016-03-01 18:33:02 | Re: Fixing wrong comment on PQmblen and PQdsplen. |
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2016-03-01 20:03:39 | Re: [NOVICE] WHERE clause not used when index is used |
| Previous Message | Tom Lane | 2016-03-01 18:32:10 | Re: [NOVICE] WHERE clause not used when index is used |