This is something we need to consider, but we'll need more evidence before making a choice. One thing that we have very little data about is how much difference it makes in the quality of planner choices.
Right, but is there a practical way to actually get this data?
If the distribution of data in the table is irregular, a higher stats target is needed to allow good planning choices. Therefore, the effect that the stats target has on planner choices depends on the regularity of the distribution of data at installations, and there is no way to know that in general AFAICS.
Also, I would expect that larger stats targets would slow down the parts of the planner that look at the stats, since there are more data values to examine. I do not have any numbers about this cost though --- do you want to try to get some?
Given the magnitude of the change (25 data elements versus 10), I wouldn't expect this to produce a major change in the total runtime of the optimizer. However, I don't know the optimizer that well, so I'll do some benchmarks when I get a chance.
-Neil
---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
