Hi, On 2020-06-12 14:37:15 -0700, Andres Freund wrote: > On 2020-06-11 11:14:02 -0700, Jeff Davis wrote: > > On Thu, 2020-06-11 at 10:45 -0700, Andres Freund wrote: > > > Did you run any performance tests? > > > > Yes, I reproduced your ~12% regression from V12, and this patch nearly > > eliminated it for me. > > I spent a fair bit of time looking at the difference. Jeff had let me > know on chat that he was still seeing some difference, but couldn't > quite figure out where that was. > > Trying it out myself, I observed that the patch helped, but not that > much. After a bit I found one major reason for why: > LookupTupleHashEntryHash() assigned the hash to pointer provided by the > caller's before doing the insertion. That ended up causing a pipeline > stall (I assume it's store forwarding, but not sure). Moving the > assignment to the caller variable to after the insertion got rid of > that.
This is still not resolved. We're right now slower than 12. It's effectively not possible to do performance comparisons right now. This was nearly two months ago. Greetings, Andres Freund
