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Display the leader apply worker's PID for parallel apply workers.

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Add leader_pid to pg_stat_subscription. leader_pid is the process ID of
the leader apply worker if this process is a parallel apply worker. If
this field is NULL, it indicates that the process is a leader apply
worker or a synchronization worker. The new column makes it easier to
distinguish parallel apply workers from other kinds of workers and helps
to identify the leader for the parallel workers corresponding to a
particular subscription.

Additionally, update the leader_pid column in pg_stat_activity as well to
display the PID of the leader apply worker for parallel apply workers.

Author: Hou Zhijie
Reviewed-by: Peter Smith, Sawada Masahiko, Amit Kapila, Shveta Mallik
Discussion: https://postgr.es/m/CAA4eK1+wyN6zpaHUkCLorEWNx75MG0xhMwcFhvjqm2KURZEAGw@mail.gmail.com
This commit is contained in:
Amit Kapila
2023-01-18 09:03:12 +05:30
parent 14bdb3f13d
commit d540a02a72
11 changed files with 106 additions and 44 deletions
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21
src/backend/utils/adt/pgstatfuncs.c
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@ -25,6 +25,7 @@
#include "pgstat.h"
#include "postmaster/bgworker_internals.h"
#include "postmaster/postmaster.h"
#include "replication/logicallauncher.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/acl.h"
@ -409,9 +410,9 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
/*
* If a PGPROC entry was retrieved, display wait events and lock
* group leader information if any. To avoid extra overhead, no
* extra lock is being held, so there is no guarantee of
* consistency across multiple rows.
* group leader or apply leader information if any. To avoid
* extra overhead, no extra lock is being held, so there is no
* guarantee of consistency across multiple rows.
*/
if (proc != NULL)
{
@ -426,14 +427,24 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
/*
* Show the leader only for active parallel workers. This
* leaves the field as NULL for the leader of a parallel
* group.
* leaves the field as NULL for the leader of a parallel group
* or the leader of parallel apply workers.
*/
if (leader && leader->pid != beentry->st_procpid)
{
values[28] = Int32GetDatum(leader->pid);
nulls[28] = false;
}
else if (beentry->st_backendType == B_BG_WORKER)
{
int leader_pid = GetLeaderApplyWorkerPid(beentry->st_procpid);
if (leader_pid != InvalidPid)
{
values[28] = Int32GetDatum(leader_pid);
nulls[28] = false;
}
}
}
if (wait_event_type)