On Wed, 26 Jul 2023 at 14:41, Alvaro Herrera <alvhe...@alvh.no-ip.org> wrote: > > Hello > > On 2023-Jul-26, Thomas wen wrote: > > > Hi Hackes: I found this page : > > https://pgsql-hackers.postgresql.narkive.com/cMxBwq65/incremental-checkopints,PostgreSQL > > no incremental checkpoints have been implemented so far. When a > > checkpoint is triggered, the performance jitter of PostgreSQL is very > > noticeable. I think incremental checkpoints should be implemented as > > soon as possible > > I think my first question is why do you think that is necessary; there > are probably other tools to achieve better performance. For example, > you may want to try making checkpoint_completion_target closer to 1, and > the checkpoint interval longer (both checkpoint_timeout and > max_wal_size). Also, changing shared_buffers may improve things. You > can try adding more RAM to the machine.
Even with all those tuning options, a significant portion of a checkpoint's IO (up to 50%) originates from FPIs in the WAL, which (in general) will most often appear at the start of each checkpoint due to each first update to a page after a checkpoint needing an FPI. If instead we WAL-logged only the pages we are about to write to disk (like MySQL's double-write buffer, but in WAL instead of a separate cyclical buffer file), then a checkpoint_completion_target close to 1 would probably solve the issue, but with "WAL-logged torn page protection at first update after checkpoint" we'll probably always have higher-than-average FPI load just after a new checkpoint. Kind regards, Matthias van de Meent Neon (https://neon.tech/)