On Mon, Jul 17, 2023 at 10:26 PM Andres Freund <and...@anarazel.de> wrote: > > Previously it was e.g. not really possible to distinguish that something like > this: > > ┌────────────────┬─────────────────┬────────────┬───────┐ > │ backend_type │ wait_event_type │ wait_event │ count │ > ├────────────────┼─────────────────┼────────────┼───────┤ > │ client backend │ LWLock │ WALInsert │ 32 │ > │ client backend │ (null) │ (null) │ 9 │ > │ walwriter │ IO │ WALWrite │ 1 │ > │ client backend │ Client │ ClientRead │ 1 │ > │ client backend │ LWLock │ WALWrite │ 1 │ > └────────────────┴─────────────────┴────────────┴───────┘ > > is a workload with a very different bottleneck than this: > > ┌────────────────┬─────────────────┬───────────────┬───────┐ > │ backend_type │ wait_event_type │ wait_event │ count │ > ├────────────────┼─────────────────┼───────────────┼───────┤ > │ client backend │ IPC │ WALWaitInsert │ 22 │ > │ client backend │ LWLock │ WALInsert │ 13 │ > │ client backend │ LWLock │ WALBufMapping │ 5 │ > │ walwriter │ (null) │ (null) │ 1 │ > │ client backend │ Client │ ClientRead │ 1 │ > │ client backend │ (null) │ (null) │ 1 │ > └────────────────┴─────────────────┴───────────────┴───────┘ > > even though they are very different > > FWIW, the former is bottlenecked by the number of WAL insertion locks, the > second is bottlenecked by copying WAL into buffers due to needing to flush > them. >
This gives a better idea of what's going on. +1 for separating these waits. -- With Regards, Amit Kapila.
