Hi, On Fri, 10 May 2024 at 19:09, Masahiko Sawada <sawada.m...@gmail.com> wrote: > > On Fri, May 10, 2024 at 7:26 PM Nazir Bilal Yavuz <byavu...@gmail.com> wrote: > > > > Hi, > > > > Thank you for working on this! > > > > On Wed, 1 May 2024 at 06:37, Masahiko Sawada <sawada.m...@gmail.com> wrote: > > > > > > Thank you for further testing! I've pushed the patch. > > > > I realized a behaviour change while looking at 'Use pgBufferUsage for > > block reporting in analyze' thread [1]. Since that change applies here > > as well, I thought it is better to mention it here. > > > > Before this commit, VacuumPageMiss did not count the blocks if its > > read was already completed by other backends [2]. Now, > > 'pgBufferUsage.local_blks_read + pgBufferUsage.shared_blks_read' > > counts every block attempted to be read; possibly double counting if > > someone else has already completed the read. > > True. IIUC there is such a difference only in HEAD but not in v15 and > v16. The following comment in WaitReadBuffers() says that it's a > traditional behavior that we count blocks as read even if someone else > has already completed its I/O: > > /* > * We count all these blocks as read by this backend. This is traditional > * behavior, but might turn out to be not true if we find that someone > * else has beaten us and completed the read of some of these blocks. In > * that case the system globally double-counts, but we traditionally don't > * count this as a "hit", and we don't have a separate counter for "miss, > * but another backend completed the read". > */ > > So I think using pgBufferUsage for (parallel) vacuum is a legitimate > usage and makes it more consistent with other parallel operations.
That sounds logical. Thank you for the clarification. -- Regards, Nazir Bilal Yavuz Microsoft
