On Mon, 2022-11-28 at 10:59 -0800, Andres Freund wrote: > On 2022-11-26 22:10:06 -0500, Reid Thompson wrote: > > - zero allocated bytes after fork to avoid double counting > > postmaster allocations > > I still don't understand this - postmaster shouldn't be counted at > all. It > doesn't have a PgBackendStatus. There simply shouldn't be any tracked > allocations from it. > > Greetings, > > Andres Freund
Hi Andres, I based this on the following. It appears to me that Postmaster populates the local variable that *my_allocated_bytes points to. That allocation is passed to forked children, and if not zeroed out, will be double counted as part of the child allocation. Is this invalid? $ ps -ef|grep postgres postgres 6389 1 0 Dec01 ? 00:00:17 /usr/sbin/pgbouncer -d /etc/pgbouncer/pgbouncer.ini rthompso 2937799 1 0 09:45 ? 00:00:00 /tmp/postgres/install/pg-stats-memory/bin/postgres -D /var/tmp/pg-stats-memory -p 5433 rthompso 2937812 2937799 0 09:45 ? 00:00:00 postgres: checkpointer rthompso 2937813 2937799 0 09:45 ? 00:00:00 postgres: background writer rthompso 2937816 2937799 0 09:45 ? 00:00:00 postgres: walwriter rthompso 2937817 2937799 0 09:45 ? 00:00:00 postgres: autovacuum launcher rthompso 2937818 2937799 0 09:45 ? 00:00:00 postgres: logical replication launcher rthompso 2938877 2636586 0 09:46 pts/4 00:00:00 /usr/lib/postgresql/12/bin/psql -h localhost -p 5433 postgres rthompso 2938909 2937799 0 09:46 ? 00:00:00 postgres: rthompso postgres 127.0.0.1(44532) idle rthompso 2942164 1987403 0 09:49 pts/3 00:00:00 grep postgres Bracketing fork_process() calls with logging to print *my_allocated_bytes immediately prior and after fork_process... To me, this indicates that the forked children for this invocation (checkpointer, walwriter, autovac launcher, client backend, autovac worker, etc) are inheriting 240672 bytes from postmaster. $ ccat logfile 2022-12-02 09:45:05.871 EST [2937799] LOG: starting PostgreSQL 16devel on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0, 64-bit 2022-12-02 09:45:05.872 EST [2937799] LOG: listening on IPv4 address "127.0.0.1", port 5433 2022-12-02 09:45:05.874 EST [2937799] LOG: listening on Unix socket "/tmp/.s.PGSQL.5433" parent StartChildProcess process. pid: 2937799 *my_allocated_bytes: 240672 parent StartChildProcess process. pid: 2937799 *my_allocated_bytes: 240672 parent StartChildProcess process. pid: 2937799 *my_allocated_bytes: 240672 child StartChildProcess process. pid: 2937812 *my_allocated_bytes: 240672 child StartChildProcess process. pid: 2937813 *my_allocated_bytes: 240672 child StartChildProcess process. pid: 2937814 *my_allocated_bytes: 240672 2022-12-02 09:45:05.884 EST [2937814] LOG: database system was shut down at 2022-12-02 09:41:13 EST parent StartChildProcess process. pid: 2937799 *my_allocated_bytes: 240672 parent StartAutoVacLauncher process. pid: 2937799 *my_allocated_bytes: 240672 child StartChildProcess process. pid: 2937816 *my_allocated_bytes: 240672 parent do_start_bgworker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacLauncher process. pid: 2937817 *my_allocated_bytes: 240672 2022-12-02 09:45:05.889 EST [2937799] LOG: database system is ready to accept connections child do_start_bgworker process. pid: 2937818 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2938417 *my_allocated_bytes: 240672 parent BackendStartup process. pid: 2937799 *my_allocated_bytes: 240672 child BackendStartup process. pid: 2938909 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2938910 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2939340 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2939665 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2940038 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2940364 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2940698 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2941317 *my_allocated_bytes: 240672 parent StartAutoVacWorker process. pid: 2937799 *my_allocated_bytes: 240672 child StartAutoVacWorker process. pid: 2941825 *my_allocated_bytes: 240672 Reid Thompson Senior Software Engineer Crunchy Data, Inc. reid.thomp...@crunchydata.com www.crunchydata.com
