On Sat, Jan 11, 2025 at 4:57 PM Junwang Zhao <zhjw...@gmail.com> wrote: > > 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
Here is my compile options: meson setup $HOME/build --prefix=$HOME/pgsql --buildtype=release and I use `objdump -D postgres | less` to see the assembly code. > > 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 -- Regards Junwang Zhao
