From 929cafe2955c375167f3a17fd22afc885a34a45b Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Tue, 3 Feb 2026 21:51:40 +0200 Subject: [PATCH 1/1] Move 'wait_event_info' to PgBackendStatus --- src/backend/storage/lmgr/proc.c | 9 ------- src/backend/utils/activity/backend_status.c | 28 +++++++++++++++++---- src/backend/utils/adt/pgstatfuncs.c | 14 ++++------- src/backend/utils/adt/waitfuncs.c | 5 ++-- src/include/storage/proc.h | 2 -- src/include/utils/backend_status.h | 10 ++++++++ 6 files changed, 40 insertions(+), 28 deletions(-) diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index fdeed0f3953..cf4fefd952f 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -521,9 +521,6 @@ InitProcess(void) Assert(MyProc->lockGroupLeader == NULL); Assert(dlist_is_empty(&MyProc->lockGroupMembers)); - /* Initialize wait event information. */ - MyProc->wait_event_info = 0; - /* Initialize fields for group transaction status update. */ MyProc->clogGroupMember = false; MyProc->clogGroupMemberXid = InvalidTransactionId; @@ -540,9 +537,6 @@ InitProcess(void) OwnLatch(&MyProc->procLatch); SwitchToSharedLatch(); - /* now that we have a proc, report wait events to shared memory */ - pgstat_set_wait_event_storage(&MyProc->wait_event_info); - /* * We might be reusing a semaphore that belonged to a failed process. So * be careful and reinitialize its value here. (This is not strictly @@ -710,9 +704,6 @@ InitAuxiliaryProcess(void) OwnLatch(&MyProc->procLatch); SwitchToSharedLatch(); - /* now that we have a proc, report wait events to shared memory */ - pgstat_set_wait_event_storage(&MyProc->wait_event_info); - /* Check that group locking fields are in a proper initial state. */ Assert(MyProc->lockGroupLeader == NULL); Assert(dlist_is_empty(&MyProc->lockGroupMembers)); diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c index c84e6536580..7c4f2c209c8 100644 --- a/src/backend/utils/activity/backend_status.c +++ b/src/backend/utils/activity/backend_status.c @@ -322,6 +322,7 @@ pgstat_bestart_initial(void) lbeentry.st_progress_command_target = InvalidOid; lbeentry.st_query_id = INT64CONST(0); lbeentry.st_plan_id = INT64CONST(0); + lbeentry.st_wait_event_info = 0; /* * we don't zero st_progress_param here to save cycles; nobody should @@ -369,6 +370,9 @@ pgstat_bestart_initial(void) #endif PGSTAT_END_WRITE_ACTIVITY(vbeentry); + + /* now that we have a backend entry, report wait events to shared memory */ + pgstat_set_wait_event_storage(unvolatize(uint32 *, &vbeentry->st_wait_event_info)); } /* ---------- @@ -585,8 +589,6 @@ pgstat_report_activity(BackendState state, const char *cmd_str) { if (beentry->st_state != STATE_DISABLED) { - volatile PGPROC *proc = MyProc; - /* * track_activities is disabled, but we last reported a * non-disabled state. As our final update, change the state and @@ -597,11 +599,11 @@ pgstat_report_activity(BackendState state, const char *cmd_str) beentry->st_state_start_timestamp = 0; beentry->st_activity_raw[0] = '\0'; beentry->st_activity_start_timestamp = 0; - /* st_xact_start_timestamp and wait_event_info are also disabled */ + /* st_xact_start_timestamp and st_wait_event_info are also disabled */ beentry->st_xact_start_timestamp = 0; beentry->st_query_id = INT64CONST(0); beentry->st_plan_id = INT64CONST(0); - proc->wait_event_info = 0; + beentry->st_wait_event_info = 0; PGSTAT_END_WRITE_ACTIVITY(beentry); } return; @@ -895,6 +897,13 @@ pgstat_read_current_status(void) if (localentry->backendStatus.st_procpid > 0) { memcpy(&localentry->backendStatus, unvolatize(PgBackendStatus *, beentry), sizeof(PgBackendStatus)); + /* + * st_wait_event_info is not protected by the changecount, so + * make sure we read it atomically. (Any half-way decent + * memcpy() implementation will read it as one word, but let's + * not assume it) + */ + localentry->backendStatus.st_wait_event_info = beentry->st_wait_event_info; /* * For each PgBackendStatus field that is a pointer, copy the @@ -1189,6 +1198,15 @@ pgstat_get_backend_type_by_proc_number(ProcNumber procNumber) return status->st_backendType; } +uint32 +pgstat_get_wait_event_info_by_proc_number(ProcNumber procNumber) +{ + volatile PgBackendStatus *status = &BackendStatusArray[procNumber]; + + /* st_wait_event_info doesn't use the changecount mechanism */ + return status->st_wait_event_info; +} + /* ---------- * cmp_lbestatus * @@ -1210,7 +1228,7 @@ cmp_lbestatus(const void *a, const void *b) * * Support function for the SQL-callable pgstat* functions. Returns * our local copy of the current-activity entry for one backend, - * or NULL if the given beid doesn't identify any known session. + * or NULL if the given procNumber doesn't identify any known session. * * The argument is the ProcNumber of the desired session * (note that this is unlike pgstat_get_local_beentry_by_index()). diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c index 73ca0bb0b7f..21dd32acf29 100644 --- a/src/backend/utils/adt/pgstatfuncs.c +++ b/src/backend/utils/adt/pgstatfuncs.c @@ -32,8 +32,6 @@ #include "utils/builtins.h" #include "utils/timestamp.h" -#define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var)))) - #define HAS_PGSTAT_PERMISSIONS(role) (has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS) || has_privs_of_role(GetUserId(), role)) #define PG_STAT_GET_RELENTRY_INT64(stat) \ @@ -469,7 +467,7 @@ pg_stat_get_activity(PG_FUNCTION_ARGS) uint32 raw_wait_event; PGPROC *leader; - raw_wait_event = UINT32_ACCESS_ONCE(proc->wait_event_info); + raw_wait_event = beentry->st_wait_event_info; wait_event_type = pgstat_get_wait_event_type(raw_wait_event); wait_event = pgstat_get_wait_event(raw_wait_event); @@ -817,15 +815,14 @@ pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS) { int32 procNumber = PG_GETARG_INT32(0); PgBackendStatus *beentry; - PGPROC *proc; const char *wait_event_type = NULL; if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL) wait_event_type = ""; else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid)) wait_event_type = ""; - else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL) - wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info); + else + wait_event_type = pgstat_get_wait_event_type(beentry->st_wait_event_info); if (!wait_event_type) PG_RETURN_NULL(); @@ -838,15 +835,14 @@ pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS) { int32 procNumber = PG_GETARG_INT32(0); PgBackendStatus *beentry; - PGPROC *proc; const char *wait_event = NULL; if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL) wait_event = ""; else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid)) wait_event = ""; - else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL) - wait_event = pgstat_get_wait_event(proc->wait_event_info); + else + wait_event = pgstat_get_wait_event(beentry->st_wait_event_info); if (!wait_event) PG_RETURN_NULL(); diff --git a/src/backend/utils/adt/waitfuncs.c b/src/backend/utils/adt/waitfuncs.c index 135e7ba8a7a..862ad8733f8 100644 --- a/src/backend/utils/adt/waitfuncs.c +++ b/src/backend/utils/adt/waitfuncs.c @@ -17,11 +17,10 @@ #include "storage/proc.h" #include "storage/procarray.h" #include "utils/array.h" +#include "utils/backend_status.h" #include "utils/fmgrprotos.h" #include "utils/wait_event.h" -#define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var)))) - /* * pg_isolation_test_session_is_blocked - support function for isolationtester @@ -56,7 +55,7 @@ pg_isolation_test_session_is_blocked(PG_FUNCTION_ARGS) if (proc == NULL) PG_RETURN_BOOL(false); /* session gone: definitely unblocked */ wait_event_type = - pgstat_get_wait_event_type(UINT32_ACCESS_ONCE(proc->wait_event_info)); + pgstat_get_wait_event_type(pgstat_get_wait_event_info_by_proc_number(GetNumberFromPGProc(proc))); if (wait_event_type && strcmp("InjectionPoint", wait_event_type) == 0) PG_RETURN_BOOL(true); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 81f1960a635..99efcbebb64 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -298,8 +298,6 @@ struct PGPROC */ TransactionId procArrayGroupMemberXid; - uint32 wait_event_info; /* proc's wait information */ - /* Support for group transaction status update. */ bool clogGroupMember; /* true, if member of clog group */ pg_atomic_uint32 clogGroupNext; /* next clog group member */ diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h index 781e48c0c10..616d1047954 100644 --- a/src/include/utils/backend_status.h +++ b/src/include/utils/backend_status.h @@ -174,6 +174,15 @@ typedef struct PgBackendStatus /* plan identifier, optionally computed using planner_hook */ int64 st_plan_id; + + /* + * Proc's wait information. This *not* protected by the changecount + * mechanism, because reading and writing an uint32 is assumed to atomic. + * This is updated very frequently, so we want to keep the overhead as + * small as possible. + */ + uint32 st_wait_event_info; + } PgBackendStatus; @@ -332,6 +341,7 @@ extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer, extern int64 pgstat_get_my_query_id(void); extern int64 pgstat_get_my_plan_id(void); extern BackendType pgstat_get_backend_type_by_proc_number(ProcNumber procNumber); +extern uint32 pgstat_get_wait_event_info_by_proc_number(ProcNumber procNumber); /* ---------- -- 2.47.3