On Mon, Mar 10, 2025 at 11:57 PM Masahiko Sawada <sawada.m...@gmail.com> wrote: > > On Sun, Mar 9, 2025 at 11:12 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > > However, in the heap vacuum phase, the leader process needed > > > to process all blocks, resulting in soft page faults while creating > > > Page Table Entries (PTEs). Without the patch, the backend process had > > > already created PTEs during the heap scan, thus preventing these > > > faults from occurring during the heap vacuum phase. > > > > > > > This part is again not clear to me because I am assuming all the data > > exists in shared buffers before the vacuum, so why the page faults > > will occur in the first place. > > IIUC PTEs are process-local data. So even if physical pages are loaded > to PostgreSQL's shared buffer (and paga caches), soft page faults (or > minor page faults)[1] can occur if these pages are not yet mapped in > its page table. >
Okay, I got your point. BTW, I noticed that even for the case where all the data is in shared_buffers, the performance improvement for workers greater than two does decrease marginally. Am I reading the data correctly? If so, what is the theory, and do we have recommendations for a parallel degree? -- With Regards, Amit Kapila.
