Add pg_shmem_allocations view.

This tells you about allocations that have been made from the main
shared memory segment. The original patch also tried to show information
about dynamic shared memory allocation as well, but I decided to
leave that problem for another time.

Andres Freund and Robert Haas, reviewed by Michael Paquier, Marti
Raudsepp, Tom Lane, Álvaro Herrera, and Kyotaro Horiguchi.

Discussion: http://postgr.es/m/20140504114417.GM12715@awork2.anarazel.de

2 files changed, 110 insertions, 2 deletions

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 2fc3e3ff90a..773edf85e78 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -547,6 +547,12 @@ CREATE VIEW pg_config AS
 REVOKE ALL on pg_config FROM PUBLIC;
 REVOKE EXECUTE ON FUNCTION pg_config() FROM PUBLIC;
 
+CREATE VIEW pg_shmem_allocations AS
+    SELECT * FROM pg_get_shmem_allocations();
+
+REVOKE ALL ON pg_shmem_allocations FROM PUBLIC;
+REVOKE EXECUTE ON FUNCTION pg_get_shmem_allocations() FROM PUBLIC;
+
 -- Statistics views
 
 CREATE VIEW pg_stat_all_tables AS
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index a4f0ec1a673..2892a573e4a 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -66,12 +66,16 @@
 #include "postgres.h"
 
 #include "access/transam.h"
+#include "fmgr.h"
+#include "funcapi.h"
 #include "miscadmin.h"
 #include "storage/lwlock.h"
 #include "storage/pg_shmem.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
+#include "utils/builtins.h"
 
+static void *ShmemAllocRaw(Size size, Size *allocated_size);
 
 /* shared memory global variables */
 
@@ -157,8 +161,9 @@ void *
 ShmemAlloc(Size size)
 {
 	void	   *newSpace;
+	Size		allocated_size;
 
-	newSpace = ShmemAllocNoError(size);
+	newSpace = ShmemAllocRaw(size, &allocated_size);
 	if (!newSpace)
 		ereport(ERROR,
 				(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -175,6 +180,20 @@ ShmemAlloc(Size size)
 void *
 ShmemAllocNoError(Size size)
 {
+	Size		allocated_size;
+
+	return ShmemAllocRaw(size, &allocated_size);
+}
+
+/*
+ * ShmemAllocRaw -- allocate align chunk and return allocated size
+ *
+ * Also sets *allocated_size to the number of bytes allocated, which will
+ * be equal to the number requested plus any padding we choose to add.
+ */
+static void *
+ShmemAllocRaw(Size size, Size *allocated_size)
+{
 	Size		newStart;
 	Size		newFree;
 	void	   *newSpace;
@@ -191,6 +210,7 @@ ShmemAllocNoError(Size size)
 	 * won't be sufficient.
 	 */
 	size = CACHELINEALIGN(size);
+	*allocated_size = size;
 
 	Assert(ShmemSegHdr != NULL);
 
@@ -441,8 +461,10 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
 	}
 	else
 	{
+		Size	allocated_size;
+
 		/* It isn't in the table yet. allocate and initialize it */
-		structPtr = ShmemAllocNoError(size);
+		structPtr = ShmemAllocRaw(size, &allocated_size);
 		if (structPtr == NULL)
 		{
 			/* out of memory; remove the failed ShmemIndex entry */
@@ -455,6 +477,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
 							name, size)));
 		}
 		result->size = size;
+		result->allocated_size = allocated_size;
 		result->location = structPtr;
 	}
 
@@ -503,3 +526,82 @@ mul_size(Size s1, Size s2)
 				 errmsg("requested shared memory size overflows size_t")));
 	return result;
 }
+
+/* SQL SRF showing allocated shared memory */
+Datum
+pg_get_shmem_allocations(PG_FUNCTION_ARGS)
+{
+#define PG_GET_SHMEM_SIZES_COLS 4
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+	HASH_SEQ_STATUS hstat;
+	ShmemIndexEnt *ent;
+	Size	named_allocated = 0;
+	Datum		values[PG_GET_SHMEM_SIZES_COLS];
+	bool		nulls[PG_GET_SHMEM_SIZES_COLS];
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	LWLockAcquire(ShmemIndexLock, LW_SHARED);
+
+	hash_seq_init(&hstat, ShmemIndex);
+
+	/* output all allocated entries */
+	memset(nulls, 0, sizeof(nulls));
+	while ((ent = (ShmemIndexEnt *) hash_seq_search(&hstat)) != NULL)
+	{
+		values[0] = CStringGetTextDatum(ent->key);
+		values[1] = Int64GetDatum((char *) ent->location - (char *) ShmemSegHdr);
+		values[2] = Int64GetDatum(ent->size);
+		values[3] = Int64GetDatum(ent->allocated_size);
+		named_allocated += ent->allocated_size;
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
+
+	/* output shared memory allocated but not counted via the shmem index */
+	values[0] = CStringGetTextDatum("<anonymous>");
+	nulls[1] = true;
+	values[2] = Int64GetDatum(ShmemSegHdr->freeoffset - named_allocated);
+	values[3] = values[2];
+	tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+
+	/* output as-of-yet unused shared memory */
+	nulls[0] = true;
+	values[1] = Int64GetDatum(ShmemSegHdr->freeoffset);
+	nulls[1] = false;
+	values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemSegHdr->freeoffset);
+	values[3] = values[2];
+	tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+
+	LWLockRelease(ShmemIndexLock);
+
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}