From cf79eb29e3a56549d7880260e76c2d1295ccadd0 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Tue, 24 Feb 2026 15:45:51 +0200 Subject: [PATCH v3 2/3] Convert pg_stat_statements to use the new interface --- .../pg_stat_statements/pg_stat_statements.c | 163 ++++++++---------- 1 file changed, 69 insertions(+), 94 deletions(-) diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c index 4a427533bd8..017387ae955 100644 --- a/contrib/pg_stat_statements/pg_stat_statements.c +++ b/contrib/pg_stat_statements/pg_stat_statements.c @@ -248,7 +248,7 @@ typedef struct pgssEntry */ typedef struct pgssSharedState { - LWLock *lock; /* protects hashtable search/modification */ + LWLockPadded lock; /* protects hashtable search/modification */ double cur_median_usage; /* current median usage in hashtable */ Size mean_query_len; /* current mean entry text length */ slock_t mutex; /* protects following fields only: */ @@ -258,13 +258,35 @@ typedef struct pgssSharedState pgssGlobalStats stats; /* global statistics for pgss */ } pgssSharedState; +/* Links to shared memory state */ +static pgssSharedState *pgss; +static HTAB *pgss_hash; + +static void pgss_shmem_init(void *arg); + +static ShmemStructDesc pgssSharedStateShmemDesc = +{ + .name = "pg_stat_statements", + .size = sizeof(pgssSharedState), + .init_fn = pgss_shmem_init, + .ptr = (void *) &pgss, +}; + +static ShmemHashDesc pgssSharedHashDesc = +{ + .name = "pg_stat_statements hash", + .init_size = 0, /* set from 'pgss_max' */ + .max_size = 0, /* set from 'pgss_max' */ + .ptr = &pgss_hash, +}; + + /*---- Local variables ----*/ /* Current nesting depth of planner/ExecutorRun/ProcessUtility calls */ static int nesting_level = 0; /* Saved hook values */ -static shmem_request_hook_type prev_shmem_request_hook = NULL; static shmem_startup_hook_type prev_shmem_startup_hook = NULL; static post_parse_analyze_hook_type prev_post_parse_analyze_hook = NULL; static planner_hook_type prev_planner_hook = NULL; @@ -274,10 +296,6 @@ static ExecutorFinish_hook_type prev_ExecutorFinish = NULL; static ExecutorEnd_hook_type prev_ExecutorEnd = NULL; static ProcessUtility_hook_type prev_ProcessUtility = NULL; -/* Links to shared memory state */ -static pgssSharedState *pgss = NULL; -static HTAB *pgss_hash = NULL; - /*---- GUC variables ----*/ typedef enum @@ -330,7 +348,6 @@ PG_FUNCTION_INFO_V1(pg_stat_statements_1_13); PG_FUNCTION_INFO_V1(pg_stat_statements); PG_FUNCTION_INFO_V1(pg_stat_statements_info); -static void pgss_shmem_request(void); static void pgss_shmem_startup(void); static void pgss_shmem_shutdown(int code, Datum arg); static void pgss_post_parse_analyze(ParseState *pstate, Query *query, @@ -365,7 +382,6 @@ static void pgss_store(const char *query, int64 queryId, static void pg_stat_statements_internal(FunctionCallInfo fcinfo, pgssVersion api_version, bool showtext); -static Size pgss_memsize(void); static pgssEntry *entry_alloc(pgssHashKey *key, Size query_offset, int query_len, int encoding, bool sticky); static void entry_dealloc(void); @@ -390,6 +406,8 @@ static int comp_location(const void *a, const void *b); void _PG_init(void) { + HASHCTL info; + /* * In order to create our shared memory area, we have to be loaded via * shared_preload_libraries. If not, fall out without hooking into any of @@ -470,11 +488,22 @@ _PG_init(void) MarkGUCPrefixReserved("pg_stat_statements"); + /* + * Register our shared memory needs, including hash table + */ + ShmemRegisterStruct(&pgssSharedStateShmemDesc); + + info.keysize = sizeof(pgssHashKey); + info.entrysize = sizeof(pgssEntry); + pgssSharedHashDesc.init_size = pgss_max; + pgssSharedHashDesc.max_size = pgss_max; + ShmemRegisterHash(&pgssSharedHashDesc, + &info, + HASH_ELEM | HASH_BLOBS); + /* * Install hooks. */ - prev_shmem_request_hook = shmem_request_hook; - shmem_request_hook = pgss_shmem_request; prev_shmem_startup_hook = shmem_startup_hook; shmem_startup_hook = pgss_shmem_startup; prev_post_parse_analyze_hook = post_parse_analyze_hook; @@ -493,31 +522,31 @@ _PG_init(void) ProcessUtility_hook = pgss_ProcessUtility; } -/* - * shmem_request hook: request additional shared resources. We'll allocate or - * attach to the shared resources in pgss_shmem_startup(). - */ static void -pgss_shmem_request(void) +pgss_shmem_init(void *arg) { - if (prev_shmem_request_hook) - prev_shmem_request_hook(); + int tranche_id; - RequestAddinShmemSpace(pgss_memsize()); - RequestNamedLWLockTranche("pg_stat_statements", 1); + tranche_id = LWLockNewTrancheId("pg_stat_statements"); + LWLockInitialize(&pgss->lock.lock, tranche_id); + pgss->cur_median_usage = ASSUMED_MEDIAN_INIT; + pgss->mean_query_len = ASSUMED_LENGTH_INIT; + SpinLockInit(&pgss->mutex); + pgss->extent = 0; + pgss->n_writers = 0; + pgss->gc_count = 0; + pgss->stats.dealloc = 0; + pgss->stats.stats_reset = GetCurrentTimestamp(); } /* - * shmem_startup hook: allocate or attach to shared memory, - * then load any pre-existing statistics from file. - * Also create and load the query-texts file, which is expected to exist - * (even if empty) while the module is enabled. + * shmem_startup hook: Load any pre-existing statistics from file at + * postmaster startup. Also create and load the query-texts file, which is + * expected to exist (even if empty) while the module is enabled. */ static void pgss_shmem_startup(void) { - bool found; - HASHCTL info; FILE *file = NULL; FILE *qfile = NULL; uint32 header; @@ -530,54 +559,14 @@ pgss_shmem_startup(void) if (prev_shmem_startup_hook) prev_shmem_startup_hook(); - /* reset in case this is a restart within the postmaster */ - pgss = NULL; - pgss_hash = NULL; + if (IsUnderPostmaster) + return; /* nothing to do in backends */ /* - * Create or attach to the shared memory state, including hash table + * Set up a shmem exit hook to dump the statistics to disk on postmaster + * (or standalone backend) exit. */ - LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE); - - pgss = ShmemInitStruct("pg_stat_statements", - sizeof(pgssSharedState), - &found); - - if (!found) - { - /* First time through ... */ - pgss->lock = &(GetNamedLWLockTranche("pg_stat_statements"))->lock; - pgss->cur_median_usage = ASSUMED_MEDIAN_INIT; - pgss->mean_query_len = ASSUMED_LENGTH_INIT; - SpinLockInit(&pgss->mutex); - pgss->extent = 0; - pgss->n_writers = 0; - pgss->gc_count = 0; - pgss->stats.dealloc = 0; - pgss->stats.stats_reset = GetCurrentTimestamp(); - } - - info.keysize = sizeof(pgssHashKey); - info.entrysize = sizeof(pgssEntry); - pgss_hash = ShmemInitHash("pg_stat_statements hash", - pgss_max, pgss_max, - &info, - HASH_ELEM | HASH_BLOBS); - - LWLockRelease(AddinShmemInitLock); - - /* - * If we're in the postmaster (or a standalone backend...), set up a shmem - * exit hook to dump the statistics to disk. - */ - if (!IsUnderPostmaster) - on_shmem_exit(pgss_shmem_shutdown, (Datum) 0); - - /* - * Done if some other process already completed our initialization. - */ - if (found) - return; + on_shmem_exit(pgss_shmem_shutdown, (Datum) 0); /* * Note: we don't bother with locks here, because there should be no other @@ -1337,7 +1326,7 @@ pgss_store(const char *query, int64 queryId, key.toplevel = (nesting_level == 0); /* Lookup the hash table entry with shared lock. */ - LWLockAcquire(pgss->lock, LW_SHARED); + LWLockAcquire(&pgss->lock.lock, LW_SHARED); entry = (pgssEntry *) hash_search(pgss_hash, &key, HASH_FIND, NULL); @@ -1358,11 +1347,11 @@ pgss_store(const char *query, int64 queryId, */ if (jstate) { - LWLockRelease(pgss->lock); + LWLockRelease(&pgss->lock.lock); norm_query = generate_normalized_query(jstate, query, query_location, &query_len); - LWLockAcquire(pgss->lock, LW_SHARED); + LWLockAcquire(&pgss->lock.lock, LW_SHARED); } /* Append new query text to file with only shared lock held */ @@ -1377,8 +1366,8 @@ pgss_store(const char *query, int64 queryId, do_gc = need_gc_qtexts(); /* Need exclusive lock to make a new hashtable entry - promote */ - LWLockRelease(pgss->lock); - LWLockAcquire(pgss->lock, LW_EXCLUSIVE); + LWLockRelease(&pgss->lock.lock); + LWLockAcquire(&pgss->lock.lock, LW_EXCLUSIVE); /* * A garbage collection may have occurred while we weren't holding the @@ -1517,7 +1506,7 @@ pgss_store(const char *query, int64 queryId, } done: - LWLockRelease(pgss->lock); + LWLockRelease(&pgss->lock.lock); /* We postpone this clean-up until we're out of the lock */ if (norm_query) @@ -1806,7 +1795,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo, * we need to partition the hash table to limit the time spent holding any * one lock. */ - LWLockAcquire(pgss->lock, LW_SHARED); + LWLockAcquire(&pgss->lock.lock, LW_SHARED); if (showtext) { @@ -2043,7 +2032,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo, tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls); } - LWLockRelease(pgss->lock); + LWLockRelease(&pgss->lock.lock); free(qbuffer); } @@ -2082,20 +2071,6 @@ pg_stat_statements_info(PG_FUNCTION_ARGS) PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls))); } -/* - * Estimate shared memory space needed. - */ -static Size -pgss_memsize(void) -{ - Size size; - - size = MAXALIGN(sizeof(pgssSharedState)); - size = add_size(size, hash_estimate_size(pgss_max, sizeof(pgssEntry))); - - return size; -} - /* * Allocate a new hashtable entry. * caller must hold an exclusive lock on pgss->lock @@ -2725,7 +2700,7 @@ entry_reset(Oid userid, Oid dbid, int64 queryid, bool minmax_only) (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("pg_stat_statements must be loaded via \"shared_preload_libraries\""))); - LWLockAcquire(pgss->lock, LW_EXCLUSIVE); + LWLockAcquire(&pgss->lock.lock, LW_EXCLUSIVE); num_entries = hash_get_num_entries(pgss_hash); stats_reset = GetCurrentTimestamp(); @@ -2819,7 +2794,7 @@ done: record_gc_qtexts(); release_lock: - LWLockRelease(pgss->lock); + LWLockRelease(&pgss->lock.lock); return stats_reset; } -- 2.47.3