v00 just the counter

Makefile

@@ -0,0 +1,21 @@
+EXTENSION = pacs
+DATA = pacs--0.0.1.sql
+REGRESS = pacs
+MODULES = pacs
+
+TAP_TESTS = 1
+
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+
+%.man.1: README.%.md
+	pandoc -s $< -o $@
+	@echo man -l $@
+
+pgbench: NPROCS=$(shell nproc)
+pgbench: NJOBS=$(shell nproc)
+pgbench: sql/pgbench.sql
+	pgbench -f $< -T 10 --progress 1 --no-vacuum \
+		-c $$(( $(NPROCS) * 4 )) \
+		-j $$(( $(NJOBS) * 4 ))

expected/pacs.out

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+CREATE EXTENSION slim;
+CREATE EXTENSION pacs;
+SELECT pacs_reset_all_measures();
+ pacs_reset_all_measures 
+-------------------------
+ 
+(1 row)
+
+-- create a measure
+SELECT pacs_create_measure('A');
+ pacs_create_measure 
+---------------------
+ 
+(1 row)
+
+-- increment it 3 times
+SELECT pacs_increment_measure('A');
+ pacs_increment_measure 
+------------------------
+ 
+(1 row)
+
+SELECT pacs_increment_measure('A');
+ pacs_increment_measure 
+------------------------
+ 
+(1 row)
+
+SELECT pacs_increment_measure('A');
+ pacs_increment_measure 
+------------------------
+ 
+(1 row)
+
+-- check measure value is 3
+SELECT pacs_get_measure('A');
+ pacs_get_measure 
+------------------
+                3
+(1 row)
+
+-- reset the measure
+SELECT pacs_reset_measure('A');
+ pacs_reset_measure 
+--------------------
+ 
+(1 row)
+
+-- should be 0 now
+SELECT pacs_get_measure('A');
+ pacs_get_measure 
+------------------
+                0
+(1 row)
+
+-- increment again
+SELECT pacs_increment_measure('A');
+ pacs_increment_measure 
+------------------------
+ 
+(1 row)
+
+-- should be 1
+SELECT pacs_get_measure('A');
+ pacs_get_measure 
+------------------
+                1
+(1 row)
+
+-- and drop the measure
+SELECT pacs_drop_measure('A');
+ pacs_drop_measure 
+-------------------
+ 
+(1 row)
+
+-- get stats from pacs (empty)
+-- SELECT * FROM pacs_get_stats();
+-- create 2 measures
+SELECT pacs_create_measure('B');
+ pacs_create_measure 
+---------------------
+ 
+(1 row)
+
+SELECT pacs_create_measure('C');
+ pacs_create_measure 
+---------------------
+ 
+(1 row)
+
+-- expect 2 measures
+-- SELECT * FROM pacs_get_stats();
+-- drop one
+SELECT pacs_drop_measure('B');
+ pacs_drop_measure 
+-------------------
+ 
+(1 row)
+
+-- so result now is 1
+-- SELECT * FROM pacs_get_stats();
+--
+-- SPECIAL CASES
+--
+-- measure A has been dropped already.
+-- but it's not erroing, as expected.
+SELECT pacs_drop_measure('A');
+ pacs_drop_measure 
+-------------------
+ 
+(1 row)
+
+-- trying to get value for an inexisting measure
+-- should ERROR
+SELECT pacs_get_measure('absent');
+ERROR:  measure "absent" does not exist
+HINT:  ensure the measure name is correct or $$ select create_measure('absent')$$ to create it
+-- reseting an inexsting measure
+-- but it's not erroing, as expected
+SELECT pacs_reset_measure('absent');
+ pacs_reset_measure 
+--------------------
+ 
+(1 row)
+
+-- the measure still does not exist
+-- so we have an error
+SELECT pacs_get_measure('absent');
+ERROR:  measure "absent" does not exist
+HINT:  ensure the measure name is correct or $$ select create_measure('absent')$$ to create it
+-- however increment always create the measure if it does not exists
+SELECT pacs_increment_measure('absent');
+ pacs_increment_measure 
+------------------------
+ 
+(1 row)
+
+-- and now we can fetch value (should be 1)
+SELECT pacs_get_measure('absent');
+ pacs_get_measure 
+------------------
+                1
+(1 row)
+
+-- and we drop the "absent" measure (yeah, it's confusing)
+SELECT pacs_drop_measure('absent');
+ pacs_drop_measure 
+-------------------
+ 
+(1 row)
+

pacs--0.0.1.sql

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+/*
+ * measures
+ */
+CREATE FUNCTION pacs_reset_all_measures()
+RETURNS void
+AS 'MODULE_PATHNAME', 'pacs_reset_all_measures'
+LANGUAGE C STRICT;
+
+CREATE FUNCTION pacs_reset_measure(measure_name Name)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pacs_reset_measure'
+LANGUAGE C STRICT;
+
+CREATE FUNCTION pacs_create_measure(measure_name Name)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pacs_create_measure'
+LANGUAGE C STRICT;
+CREATE FUNCTION pacs_drop_measure(measure_name Name)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pacs_drop_measure'
+LANGUAGE C STRICT;
+
+CREATE FUNCTION pacs_increment_measure(measure_name Name)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pacs_increment_measure'
+LANGUAGE C STRICT;
+CREATE FUNCTION pacs_get_measure(measure_name Name)
+RETURNS bigint
+AS 'MODULE_PATHNAME', 'pacs_get_measure'
+LANGUAGE C STRICT;

pacs.c

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+/*--------------------------------------------------------------------------
+ *
+ * pacs.c
+ *		Code for easier management of "measures".
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+#include "fmgr.h"
+
+#include "common/hashfn.h"
+#include "pgstat.h"
+#include "utils/builtins.h"
+#include "utils/pgstat_internal.h"
+
+#include "pacs.h"
+
+PG_MODULE_MAGIC;
+
+/* structure for measure */
+typedef struct MeasureStatEntry
+{
+    PgStat_Counter measure;
+} MeasureStatEntry;
+
+/* boilerplace structure for all measures */
+typedef struct MeasuresStatShared
+{
+    PgStatShared_Common header;
+    MeasureStatEntry stats;
+} MeasuresStatShared;
+
+/* boilerplate declaration */
+static bool measure_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
+
+/* declare our measures stats */
+static const PgStat_KindInfo measures = {
+    .name = "measures",
+    .fixed_amount = false,
+
+    /* Measures are system-wide */
+    .accessed_across_databases = true,
+
+    .shared_size = sizeof(MeasuresStatShared),
+    .shared_data_off = offsetof(MeasuresStatShared, stats),
+    .shared_data_len = sizeof(((MeasuresStatShared *) 0)->stats),
+    .pending_size = sizeof(MeasureStatEntry),
+    .flush_pending_cb = measure_flush_cb,
+};
+
+/*
+ * Compute stats entry idx from measure name with an 8-byte hash.
+ */
+#define PGSTAT_MEASURE_IDX(name) hash_bytes_extended((const unsigned char *) name, strlen(name), 0)
+
+/*
+ * Kind ID reserved for statistics of measures.
+ */
+#define PGSTAT_KIND_MEASURE	(PGSTAT_KIND_CUSTOM_MIN + 1)
+
+/* Track if stats are loaded */
+static bool measures_loaded = false;
+
+void
+_PG_init(void)
+{
+	if (!process_shared_preload_libraries_in_progress)
+		return;
+
+   ereport(LOG,
+            (errmsg("Module pacs is starting"),
+             errdetail("providing advanced stats structures.")));
+    pgstat_register_kind(PGSTAT_KIND_MEASURE, &measures);
+
+    /* mark stats as loaded */
+    measures_loaded = true;
+}
+
+/*
+ * Callback for flushing a measure
+ */
+static bool
+measure_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
+{
+    MeasureStatEntry *localent;
+    MeasuresStatShared *shfuncent;
+
+    localent = (MeasureStatEntry *) entry_ref->pending;
+    shfuncent = (MeasuresStatShared *) entry_ref->shared_stats;
+
+    if (!pgstat_lock_entry(entry_ref, nowait))
+        return false;
+
+    shfuncent->stats.measure += localent->measure;
+    return true;
+}
+
+static void
+check_loaded()
+{
+    if (!measures_loaded)
+        ereport(ERROR,
+                (errcode(ERRCODE_UNDEFINED_OBJECT),
+                 errmsg("measures module not loaded"),
+                 errhint("check shared_preload_libraries")));
+}
+
+/*
+ * The following code contains:
+ * - the exported C functions
+ * - the SQL API
+ */
+/*
+ * Create a measure
+ */
+PGDLLEXPORT void
+pacsCreateMeasure(const char *name)
+{
+    PgStat_EntryRef *entry_ref;
+    MeasuresStatShared *shstatent;
+
+    /* error if disabled */
+    check_loaded();
+
+    entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_MEASURE, InvalidOid,
+                                            PGSTAT_MEASURE_IDX(name), false);
+    shstatent = (MeasuresStatShared *) entry_ref->shared_stats;
+
+    /* initialize shared memory data */
+    memset(&shstatent->stats, 0, sizeof(shstatent->stats));
+    pgstat_unlock_entry(entry_ref);
+}
+
+/*
+ * SQL API
+ */
+PG_FUNCTION_INFO_V1(pacs_create_measure);
+Datum
+pacs_create_measure(PG_FUNCTION_ARGS)
+{
+    Name              name;
+
+    name = PG_GETARG_NAME(0);
+    pacsCreateMeasure(NameStr(*name));
+    PG_RETURN_VOID();
+}
+
+/*
+ * Drop a measure
+ *
+ * XXX register to create, drop to unregister...
+ */
+PGDLLEXPORT void
+pacsDropMeasure(const char *name)
+{
+    /* error if disabled */
+    check_loaded();
+
+    /* drop and on faillure inform for later garbage collection */
+    if (!pgstat_drop_entry(PGSTAT_KIND_MEASURE, InvalidOid,
+                           PGSTAT_MEASURE_IDX(name)))
+        pgstat_request_entry_refs_gc();
+}
+
+PG_FUNCTION_INFO_V1(pacs_drop_measure);
+Datum
+pacs_drop_measure(PG_FUNCTION_ARGS)
+{
+    Name              name;
+
+    name = PG_GETARG_NAME(0);
+    pacsDropMeasure(NameStr(*name));
+    PG_RETURN_VOID();
+}
+
+/*
+ * Increment a measure
+ *
+ * By design, PostgreSQL does create the measure if absent!
+ *
+ * we do not manage ereport() here to not add overhead.
+ * XXX is it accurate ?
+ */
+PGDLLEXPORT void
+pacsIncrementMeasure(const char *name)
+{
+    PgStat_EntryRef *entry_ref;
+    MeasuresStatShared *shstatent;
+    MeasureStatEntry *statent;
+
+    /* quick leave if disabled */
+    if (!measures_loaded)
+      return;
+
+    entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_MEASURE, InvalidOid,
+                                            PGSTAT_MEASURE_IDX(name), false);
+
+    shstatent = (MeasuresStatShared *) entry_ref->shared_stats;
+    statent = &shstatent->stats;
+
+    /* Update the measure */
+    statent->measure++;
+
+    pgstat_unlock_entry(entry_ref);
+}
+
+PG_FUNCTION_INFO_V1(pacs_increment_measure);
+Datum
+pacs_increment_measure(PG_FUNCTION_ARGS)
+{
+    Name              name;
+
+    name = PG_GETARG_NAME(0);
+    pacsIncrementMeasure(NameStr(*name));
+    PG_RETURN_VOID();
+}
+
+/*
+ * Support function for the SQL-callable functions. Returns
+ * a pointer to the measure struct.
+ */
+static MeasureStatEntry *
+pacsGetMeasure(const char *name)
+{
+    MeasureStatEntry *entry = NULL;
+
+    /* error if disabled */
+    check_loaded();
+
+    /* Compile the lookup key as a hash of the measure name */
+    entry = (MeasureStatEntry *) pgstat_fetch_entry(PGSTAT_KIND_MEASURE,
+                                                    InvalidOid,
+                                                    PGSTAT_MEASURE_IDX(name));
+    return entry;
+}
+
+/*
+ * SQL function returning the measure current value.
+ */
+PG_FUNCTION_INFO_V1(pacs_get_measure);
+Datum
+pacs_get_measure(PG_FUNCTION_ARGS)
+{
+    MeasureStatEntry  *entry;
+    Name              name;
+
+    name = PG_GETARG_NAME(0);
+
+    entry = pacsGetMeasure(NameStr(*name));
+    if (entry == NULL)
+        ereport(ERROR,
+                (errcode(ERRCODE_UNDEFINED_OBJECT),
+                errmsg("measure \"%s\" does not exist",
+                       NameStr(*name)),
+                errhint("ensure the measure name is correct or "
+                        "$$ select create_measure('%s')$$ to create it",
+                        NameStr(*name))));
+
+    PG_RETURN_INT64(entry->measure);
+}
+
+/*
+ * Reset a measure
+ */
+PGDLLEXPORT void
+pacsResetMeasure(const char *name)
+{
+    /* error if disabled */
+    check_loaded();
+    pgstat_reset_entry(PGSTAT_KIND_MEASURE, InvalidOid,
+                       PGSTAT_MEASURE_IDX(name), 0);
+    return;
+}
+
+/*
+ * SQL function reseting the measure(s)
+ */
+PG_FUNCTION_INFO_V1(pacs_reset_measure);
+Datum
+pacs_reset_measure(PG_FUNCTION_ARGS)
+{
+    Name    name;
+    name = PG_GETARG_NAME(0);
+    pacsResetMeasure(NameStr(*name));
+    PG_RETURN_VOID();
+}
+
+/*
+ * Reset a measure
+ */
+PGDLLEXPORT void
+pacsResetAllMeasures(void)
+{
+    /* error if disabled */
+    check_loaded();
+    pgstat_reset_of_kind(PGSTAT_KIND_MEASURE);
+    return;
+}
+
+PG_FUNCTION_INFO_V1(pacs_reset_all_measures);
+Datum
+pacs_reset_all_measures(PG_FUNCTION_ARGS)
+{
+    pacsResetAllMeasures();
+    PG_RETURN_VOID();
+}
+
+// PG_FUNCTION_INFO_V1(pacs_list_all_measures);
+// PGDLLEXPORT void
+// pacs_list_all_measures(PgStat_Kind kind)
+// {
+//     HASH_SEQ_STATUS status;
+//     PgStat_EntryRef *entry_ref;
+//
+//     const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+//     if (!kind_info || !kind_info->hash_table)
+//     {
+//         elog(ERROR, "Invalid or unsupported statistics kind.");
+//         return;
+//     }
+//
+//     hash_seq_init(&status, kind_info->hash_table);
+//
+//     while ((entry_ref = hash_seq_search(&status)) != NULL)
+//     {
+//         elog(INFO, "Key for kind %d: %u/%llu", kind,
+//             entry_ref->key.dboid, (unsigned long long)entry_ref->key.objid);
+//     }
+// }

pacs.control

@@ -0,0 +1,5 @@
+comment = 'Provides PostgresSQL Advanced Cumulative Statistics'
+default_version = '0.0.1'
+relocatable = true
+module_pathname = '$libdir/pacs'
+requires = 'slim'

pacs.h

@@ -0,0 +1,29 @@
+/*--------------------------------------------------------------------------
+ *
+ * pacs.h
+ *		Definitions for easier statistics management.
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#ifndef PACS
+#define PACS
+
+extern void RegisterMeasuresInPgStat(void);
+
+/* creating/dropping stats */
+extern void pacsCreateMeasure(const char *name);
+extern void pacsDropMeasure(const char *name);
+
+/* working with stats content */
+extern void pacsIncrementMeasure(const char *name);
+extern void pacsResetAllMeasures(void);
+extern void pacsResetMeasure(const char *name);
+
+/* statsmgr_stats.c */
+extern void RegisterPacsInPgStat(void);
+
+#endif

sql/pacs.sql

@@ -0,0 +1,59 @@
+CREATE EXTENSION slim;
+CREATE EXTENSION pacs;
+
+SELECT pacs_reset_all_measures();
+
+-- create a measure
+SELECT pacs_create_measure('A');
+-- increment it 3 times
+SELECT pacs_increment_measure('A');
+SELECT pacs_increment_measure('A');
+SELECT pacs_increment_measure('A');
+-- check measure value is 3
+SELECT pacs_get_measure('A');
+-- reset the measure
+SELECT pacs_reset_measure('A');
+-- should be 0 now
+SELECT pacs_get_measure('A');
+-- increment again
+SELECT pacs_increment_measure('A');
+-- should be 1
+SELECT pacs_get_measure('A');
+-- and drop the measure
+SELECT pacs_drop_measure('A');
+
+-- get stats from pacs (empty)
+-- SELECT * FROM pacs_get_stats();
+-- create 2 measures
+SELECT pacs_create_measure('B');
+SELECT pacs_create_measure('C');
+-- expect 2 measures
+-- SELECT * FROM pacs_get_stats();
+-- drop one
+SELECT pacs_drop_measure('B');
+-- so result now is 1
+-- SELECT * FROM pacs_get_stats();
+
+--
+-- SPECIAL CASES
+--
+-- measure A has been dropped already.
+-- but it's not erroing, as expected.
+SELECT pacs_drop_measure('A');
+
+-- trying to get value for an inexisting measure
+-- should ERROR
+SELECT pacs_get_measure('absent');
+
+-- reseting an inexsting measure
+-- but it's not erroing, as expected
+SELECT pacs_reset_measure('absent');
+-- the measure still does not exist
+-- so we have an error
+SELECT pacs_get_measure('absent');
+-- however increment always create the measure if it does not exists
+SELECT pacs_increment_measure('absent');
+-- and now we can fetch value (should be 1)
+SELECT pacs_get_measure('absent');
+-- and we drop the "absent" measure (yeah, it's confusing)
+SELECT pacs_drop_measure('absent');