On Tue, Nov 12, 2013 at 2:47 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> That's right, we store 90 days and roll up data older than that into a
> different table.
Ah-hah. The default statistics target is 100, so indeed ANALYZE is going to be able to fit every date entry in the table into the most-common-values list. In this situation, you'd rather that there were some uncertainty left. Given that the distribution of the date column is (I assume) pretty level, you don't really need full information about this column. I'd try backing off the stats target for the date column (and only the date column --- see ALTER TABLE SET STATISTICS) to 50 or even less.
That was it! I set it to 50 on all the 90-days tables and now we no longer see that regular increase in disk reads between midnight of the new day and the 1:37am re-analyze.
