Tom Lane wrote: > Russell Smith <mr-russ@xxxxxxxxxx> writes: >> It is possible that analyze is not getting the number of dead rows >> right? > > Hah, I think you are on to something. ANALYZE is telling the truth about > how many "dead" rows it saw, but its notion of "dead" is "not good > according to SnapshotNow". Thus, rows inserted by a not-yet-committed > transaction would be counted as dead. So if these are background > auto-analyzes being done in parallel with inserting transactions that run > for awhile, They are. > seeing a few not-yet-committed rows would be unsurprising. That is a very interesting possibility. I can see that it is certainly a possible explanation, since my insert transactions take between 0.04 to 0.1 minutes (sorry, decimal stopwatch) of real time, typically putting 1700 rows into about a half dozen tables. And the ANALYZE is whatever autovacuum chooses to do. So if new not-yet-committed rows are considered dead, that would be a sufficient explanation. So I am, retroactively, unsurprised. > I wonder if that is worth fixing? I'm not especially concerned about the > cosmetic aspect of it, but if we mistakenly launch an autovacuum on the > strength of an inflated estimate of dead rows, that could be costly. > Well, since I was more interested in the explanation than in the fixing, in that sense I do not care if it is fixed or not. While it may create a slight slowdown (if it is an error), the applications run "fast enough." I would not even get the fix until Red Hat get around to putting it in (I run postgresql-8.1.9-1.el5 that is in their RHEL5 distribution), that probably will not be until RHEL6 and the soonest, and I will probably skip that one and wait until RHEL7 comes out in about 3 years. But somewhere perhaps a reminder of this should be placed where someone like me would find it, so we would not have to go through this again for someone else. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 22:05:01 up 22 days, 15:23, 0 users, load average: 4.16, 4.22, 4.10 ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
