| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Parallel append plan instability/randomness |
| Date: | 2018-01-08 05:56:21 |
| Message-ID: | 7400.1515390981@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> writes:
> The fact that b_star gets moved from 5th position to the first
> position in the scans, indicates that it's cost shoots up from 1.04 to
> a value greater than 1.16. It does not look like a case where two
> costs are almost same due to which their positions swap sometimes. I
> am trying to figure out what else can it be ...
The gut feeling I had upon seeing the failure was that the plan shape
depends on the order in which rows happen to be read from the system
catalogs by a heapscan. I've not tried to run that idea to ground yet.
regards, tom lane
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