On Fri, Sep 28, 2018 at 10:58 PM Andrey Lepikhov <a.lepik...@postgrespro.ru> wrote: > I am reviewing this patch too. And join to Peter Eisentraut opinion > about splitting the patch into a hierarchy of two or three patches: > "functional" - tid stuff and "optimizational" - suffix truncation & > splitting. My reasons are simplification of code review, investigation > and benchmarking.
As I mentioned to Peter, I don't think that I can split out the heap TID stuff from the suffix truncation stuff. At least not without making the patch even more complicated, for no benefit. I will split out the "brain" of the patch (the _bt_findsplitloc() stuff, which decides on a split point using sophisticated rules) from the "brawn" (the actually changes to how index scans work, including the heap TID stuff, as well as the code for actually physically performing suffix truncation). The brain of the patch is where most of the complexity is, as well as most of the code. The brawn of the patch is _totally unusable_ without intelligence around split points, but I'll split things up along those lines anyway. Doing so should make the whole design a little easier to see follow. > Now benchmarking is not clear. Possible performance degradation from TID > ordering interfere with positive effects from the optimizations in > non-trivial way. Is there any evidence of a regression in the last 2 versions? I've been using pgbench, which didn't show any. That's not a sympathetic case for the patch, though it would be nice to confirm if there was some small improvement there. I've seen contradictory results (slight improvements and slight regressions), but that was with a much earlier version, so it just isn't relevant now. pgbench is mostly interesting as a thing that we want to avoid regressing. Once I post the next version, it would be great if somebody could use HammerDB's OLTP test, which seems like the best fair use implementation of TPC-C that's available. I would like to make that the "this is why you should care, even if you happen to not believe in the patch's strategic importance" benchmark. TPC-C is clearly the most influential database benchmark ever, so I think that that's a fair request. (See the TPC-C commentary at https://www.hammerdb.com/docs/ch03s02.html, for example.) -- Peter Geoghegan
