> If I have a freshly CLUSTERed table and queries that want to do a
> merge join, it seems to me that quite a bit of time is spent
> unnecessarily sorting the already-sorted table. An example such
> query I found in my log files is shown below. If I read the
> EXPLAIN ANALYZE output correctly, it's saying that roughly half
> the time (570-269 = 300 out of 670 ms) was spent sorting the
> already sorted data.

It still has to sort because the clustering isn't guarenteed to be 100%.   
However, such sorts should be very quick as they have little work to do.

Looking at your analyze, though, I think it's not the sort that's taking the 
time as it is that the full sorted entity_id column won't fit in work_mem.  
Try increasing it?


Josh Berkus
Aglio Database Solutions
San Francisco

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