On Fri, Jan 10, 2025 at 10:49 PM Vladlen Popolitov <v.popoli...@postgrespro.ru> wrote: > > Amit Langote писал(а) 2025-01-10 18:22: > > On Fri, Jan 10, 2025 at 7:36 PM David Rowley <dgrowle...@gmail.com> > > wrote: > >> On Fri, 10 Jan 2025 at 22:53, Vladlen Popolitov > >> <v.popoli...@postgrespro.ru> wrote: > >> > In case of query > >> > select count(*) from test_table where a_1 = 1000000; > >> > I would expect increase of query time due to additional if...else . It > >> > is not clear > >> > what code was eliminated to decrease query time. > >> > >> Are you talking about the code added to ExecInitSeqScan() to determine > >> which node function to call? If so, that's only called during executor > >> startup. The idea here is to reduce the branching during execution by > >> calling one of those special functions which has a more specialised > >> version of the ExecScan code for the particular purpose it's going to > >> be used for. > > > > Looks like I hadn't mentioned this key aspect of the patch in the > > commit message, so did that in the attached. > > > > Vladlen, does what David wrote and the new commit message answer your > > question(s)? > > Hi Amit, > > Yes, David clarified the idea, but it is still hard to believe in 5% of > improvements. > The query > select count(*) from test_table where a_1 = 1000000; > has both qual and projection, and ExecScanExtended() will be generated > similar to ExecScan() (the same not NULL values to check in if()). > Do you have some scripts to reproduce your benchmark?
The benchmark is provided [0]. Here is a rough comparison of compiled variants' assembly code. <ExecSeqScan>: start 2b8590, end 2b868c => 252 <ExecSeqScanWithProject>: start 2b8034, end 2b8140 => 268 <ExecSeqScanWithQual>: start 2b8144, end 2b831c => 472 <ExecSeqScanWithQualProject>: start 2b8320, end 2b858c => 620 Before Amit's optimization, it was basically called the ExecSeqScanWithQualProject, you can see the other 3 variants all have some reduction in function size. > -- > Best regards, > > Vladlen Popolitov. [0] https://docs.google.com/spreadsheets/d/1AsJOUgIfSsYIJUJwbXk4aO9FVOFOrBCvrfmdQYkHIw4/edit?usp=sharing -- Regards Junwang Zhao
