| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Greg Smith <gsmith(at)gregsmith(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: I/O on select count(*) |
| Date: | 2008-05-15 07:07:09 |
| Message-ID: | 28388.1210835229@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Greg Smith <gsmith(at)gregsmith(dot)com> writes:
> ... To put that another way: if I've run a manual vacuum, is it true
> that it will have updated all the hint bits to XMIN_COMMITTED for all the
> tuples that were all done when the vacuum started?
Any examination whatsoever of a tuple --- whether by vacuum or any
ordinary DML operation --- will update its hint bits to match the
commit/abort status of the inserting/deleting transaction(s) as of
the instant of the examination. Your statement above is true but
is weaker than reality.
regards, tom lane
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