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Fix collector hangs if requesting backend is gone #122

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876c7e9
Fix collector hangs if requesting backend is gone
Medvecrab Aug 6, 2026
2c22a04
Remove PG-13 support
Medvecrab Aug 6, 2026
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6 changes: 3 additions & 3 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ PostgreSQL installation. It is available from
[github](https://github.com/postgrespro/pg_wait_sampling)
under the same license as
[PostgreSQL](http://www.postgresql.org/about/licence/)
and supports PostgreSQL 13+.
and supports PostgreSQL 14+.

Installation
------------
Expand All @@ -62,10 +62,10 @@ repository: https://download.postgresql.org/pub/repos/
Manual build
------------

`pg_wait_sampling` is PostgreSQL extension which requires PostgreSQL 13 or
`pg_wait_sampling` is PostgreSQL extension which requires PostgreSQL 14 or
higher. Before build and install you should ensure following:

* PostgreSQL version is 13 or higher.
* PostgreSQL version is 14 or higher.
* You have development package of PostgreSQL installed or you built
PostgreSQL from source.
* Your PATH variable is configured so that `pg_config` command available, or
Expand Down
97 changes: 31 additions & 66 deletions pg_wait_sampling.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
* pg_wait_sampling.c
* Track information about wait events.
*
* Copyright (c) 2015-2025, Postgres Professional
* Copyright (c) 2015-2026, Postgres Professional
*
* IDENTIFICATION
* contrib/pg_wait_sampling/pg_wait_sampling.c
Expand Down Expand Up @@ -75,9 +75,7 @@ static shmem_request_hook_type prev_shmem_request_hook = NULL;
static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
static PGPROC *search_proc(int backendPid);
static PlannedStmt *pgws_planner_hook(Query *parse,
#if PG_VERSION_NUM >= 130000
const char *query_string,
#endif
int cursorOptions, ParamListInfo boundParams
#if PG_VERSION_NUM >= 190000
, ExplainState *es
Expand All @@ -87,26 +85,20 @@ static void pgws_ExecutorStart(QueryDesc *queryDesc, int eflags);
static void pgws_ExecutorRun(QueryDesc *queryDesc,
ScanDirection direction,
uint64 count
#if PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 180000
#if PG_VERSION_NUM < 180000
,bool execute_once
#endif
);
static void pgws_ExecutorFinish(QueryDesc *queryDesc);
static void pgws_ExecutorEnd(QueryDesc *queryDesc);
static void pgws_ProcessUtility(PlannedStmt *pstmt,
const char *queryString,
#if PG_VERSION_NUM >= 140000
bool readOnlyTree,
#endif
ProcessUtilityContext context,
ParamListInfo params,
QueryEnvironment *queryEnv,
DestReceiver *dest,
#if PG_VERSION_NUM >= 130000
QueryCompletion *qc
#else
char *completionTag
#endif
);

/*---- GUC variables ----*/
Expand Down Expand Up @@ -654,6 +646,16 @@ receive_array(SHMRequest request, Size item_size, Size *count)
char *ptr;
MemoryContext oldctx;

/* Check that the collector was started to avoid NULL pointer dereference */
if (!pgws_collector_hdr->latch)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector wasn't started")));

/* Check that the collector exists to avoid getting stuck in shm_mq_receive */
if (pgws_collector_hdr->latch->owner_pid == 0)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector doesn't exist")));

/* Ensure nobody else trying to send request to queue */
pgws_init_lock_tag(&queueTag, PGWS_QUEUE_LOCK);
LockAcquire(&queueTag, ExclusiveLock, false, false);
Expand All @@ -664,19 +666,6 @@ receive_array(SHMRequest request, Size item_size, Size *count)
pgws_collector_hdr->request = request;
LockRelease(&collectorTag, ExclusiveLock, false);

/*
* Check that the collector was started to avoid NULL
* pointer dereference.
*/
if (!pgws_collector_hdr->latch)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector wasn't started")));

/* Check that the collector exists to avoid getting stuck in shm_mq_receive */
if (pgws_collector_hdr->latch->owner_pid == 0)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector doesn't exist")));

SetLatch(pgws_collector_hdr->latch);

shm_mq_set_receiver(recv_mq, MyProc);
Expand Down Expand Up @@ -837,6 +826,16 @@ pg_wait_sampling_reset_profile(PG_FUNCTION_ARGS)

check_shmem();

/* Check that the collector was started to avoid NULL pointer dereference */
if (!pgws_collector_hdr->latch)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector wasn't started")));

/* Check that the collector exists to avoid setting pgws_collector_hdr->request */
if (pgws_collector_hdr->latch->owner_pid == 0)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector doesn't exist")));

pgws_init_lock_tag(&queueTag, PGWS_QUEUE_LOCK);

LockAcquire(&queueTag, ExclusiveLock, false, false);
Expand All @@ -846,14 +845,6 @@ pg_wait_sampling_reset_profile(PG_FUNCTION_ARGS)
pgws_collector_hdr->request = PROFILE_RESET;
LockRelease(&collectorTag, ExclusiveLock, false);

/*
* Check that the collector was started to avoid NULL
* pointer dereference.
*/
if (!pgws_collector_hdr->latch)
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
errmsg("pg_wait_sampling collector wasn't started")));

SetLatch(pgws_collector_hdr->latch);

LockRelease(&queueTag, ExclusiveLock, false);
Expand Down Expand Up @@ -959,9 +950,7 @@ pg_wait_sampling_get_history(PG_FUNCTION_ARGS)
*/
static PlannedStmt *
pgws_planner_hook(Query *parse,
#if PG_VERSION_NUM >= 130000
const char *query_string,
#endif
int cursorOptions,
ParamListInfo boundParams
#if PG_VERSION_NUM >= 190000
Expand All @@ -985,19 +974,15 @@ pgws_planner_hook(Query *parse,
/* Invoke original hook if needed */
if (planner_hook_next)
result = planner_hook_next(parse,
#if PG_VERSION_NUM >= 130000
query_string,
#endif
cursorOptions, boundParams
#if PG_VERSION_NUM >= 190000
, es
#endif
);
else
result = standard_planner(parse,
#if PG_VERSION_NUM >= 130000
query_string,
#endif
cursorOptions, boundParams
#if PG_VERSION_NUM >= 190000
, es
Expand Down Expand Up @@ -1043,7 +1028,7 @@ static void
pgws_ExecutorRun(QueryDesc *queryDesc,
ScanDirection direction,
uint64 count
#if PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 180000
#if PG_VERSION_NUM < 180000
,bool execute_once
#endif
)
Expand All @@ -1055,16 +1040,16 @@ pgws_ExecutorRun(QueryDesc *queryDesc,
PG_TRY();
{
if (prev_ExecutorRun)
#if PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 180000
prev_ExecutorRun(queryDesc, direction, count, execute_once);
#else
#if PG_VERSION_NUM >= 180000
prev_ExecutorRun(queryDesc, direction, count);
#else
prev_ExecutorRun(queryDesc, direction, count, execute_once);
#endif
else
#if PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 180000
standard_ExecutorRun(queryDesc, direction, count, execute_once);
#else
#if PG_VERSION_NUM >= 180000
standard_ExecutorRun(queryDesc, direction, count);
#else
standard_ExecutorRun(queryDesc, direction, count, execute_once);
#endif
nesting_level--;
if (nesting_level == 0)
Expand Down Expand Up @@ -1132,18 +1117,12 @@ pgws_ExecutorEnd(QueryDesc *queryDesc)
static void
pgws_ProcessUtility(PlannedStmt *pstmt,
const char *queryString,
#if PG_VERSION_NUM >= 140000
bool readOnlyTree,
#endif
ProcessUtilityContext context,
ParamListInfo params,
QueryEnvironment *queryEnv,
DestReceiver *dest,
#if PG_VERSION_NUM >= 130000
QueryCompletion *qc
#else
char *completionTag
#endif
)
{
int i = MyProc - ProcGlobal->allProcs;
Expand All @@ -1160,30 +1139,16 @@ pgws_ProcessUtility(PlannedStmt *pstmt,
{
if (prev_ProcessUtility)
prev_ProcessUtility(pstmt, queryString,
#if PG_VERSION_NUM >= 140000
readOnlyTree,
#endif
context, params, queryEnv,
dest,
#if PG_VERSION_NUM >= 130000
qc
#else
completionTag
#endif
);
qc);
else
standard_ProcessUtility(pstmt, queryString,
#if PG_VERSION_NUM >= 140000
readOnlyTree,
#endif
context, params, queryEnv,
dest,
#if PG_VERSION_NUM >= 130000
qc
#else
completionTag
#endif
);
qc);
nesting_level--;
if (nesting_level == 0)
pgws_proc_queryids[i] = UINT64CONST(0);
Expand Down
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