| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | t(dot)katsumata1122(at)gmail(dot)com |
| Cc: | pgsql-bugs(at)postgresql(dot)org |
| Subject: | Re: BUG #12584: small bug about estimation of rows |
| Date: | 2015-01-18 22:06:37 |
| Message-ID: | 20684.1421618797@sss.pgh.pa.us |
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| Lists: | pgsql-bugs |
t(dot)katsumata1122(at)gmail(dot)com writes:
> I found a bug about estimating rows without pg_class.reltuples.
> ...
> It should be using sizeof(ItemIdData) at line 512, so the estimated rows
> should be "rows=2260".
> I could understand ignoring alignment of data here from comment of the
> source code,
> but I couldn't find the reason of using sizeof(ItemPointerData) at this
> point.
> Usually this would not cause big problem, but it seems odd to me.
> Is there any reason to use sizeof(ItemPointerData) ?
You're absolutely right, that's a thinko. Adjusted in HEAD. I'm not
inclined to back-patch it though, since there's a risk of changing
plan choices which is something we don't like to do in stable branches
unless the planner is clearly doing the wrong thing.
regards, tom lane
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| Previous Message | pgsql-004 | 2015-01-18 17:50:56 | BUG #12589: Poor randomness from random() with some seeds; poor resolution |