Re: Update using primary key slow

Denis <denis(dot)sailer(at)yellowbook(dot)com> writes:
> tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane) wrote in
> news:19722(dot)1130429883(at)sss(dot)pgh(dot)pa(dot)us:
>> The 183 msec is the time needed to *fetch* the row, not the time to
>> update it. So it could well be that the other time is just the time
>> needed to update the table and indexes. If this seems slower than
>> your hardware ought to be able to handle, I'd wonder about how
>> recently the table has been vacuumed.

> Here is the latest vacuum today.

> INFO: "contract": removed 64146 row versions in 26115 pages
> DETAIL: CPU 1.94s/2.55u sec elapsed 7.78 sec.
> INFO: "contract": found 64146 removable, 5106307 nonremovable row
> versions in 129154 pages
> DETAIL: 890 dead row versions cannot be removed yet.
> There were 1905028 unused item pointers.

The "unused item pointers" number seems a bit high, but otherwise that
looks pretty reasonable.

Is it possible that the particular row you were updating has been
updated quite a lot of times since the last vacuum? Or even quite
a few times within a single transaction? The only thing I can think
of that would explain such a slow fetch is if the code has to reject
a bunch of recently-dead versions of the row.

regards, tom lane