Add pg_backend_memory_contexts system view.

This view displays the usages of all the memory contexts of the server
process attached to the current session. This information is useful to
investigate the cause of backend-local memory bloat.

This information can be also collected by calling
MemoryContextStats(TopMemoryContext) via a debugger. But this technique
cannot be uesd in some environments because no debugger is available there.
And it outputs lots of text messages and it's not easy to analyze them.
So, pg_backend_memory_contexts view allows us to access to backend-local
memory contexts information more easily.

Bump catalog version.

Author: Atsushi Torikoshi, Fujii Masao
Reviewed-by: Tatsuhito Kasahara, Andres Freund, Daniel Gustafsson, Robert Haas, Michael Paquier
Discussion: https://postgr.es/m/72a656e0f71d0860161e0b3f67e4d771@oss.nttdata.com

5 files changed, 161 insertions, 1 deletions

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 8625cbeab6e..ba5a23ac252 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -554,6 +554,9 @@ CREATE VIEW pg_shmem_allocations AS
 REVOKE ALL ON pg_shmem_allocations FROM PUBLIC;
 REVOKE EXECUTE ON FUNCTION pg_get_shmem_allocations() FROM PUBLIC;
 
+CREATE VIEW pg_backend_memory_contexts AS
+    SELECT * FROM pg_get_backend_memory_contexts();
+
 -- Statistics views
 
 CREATE VIEW pg_stat_all_tables AS
diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index abda22fa570..d9bb2499db7 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -21,8 +21,10 @@
 
 #include "postgres.h"
 
+#include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "utils/builtins.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
 
@@ -67,6 +69,12 @@ static void MemoryContextStatsPrint(MemoryContext context, void *passthru,
 #define AssertNotInCriticalSection(context) \
 	Assert(CritSectionCount == 0 || (context)->allowInCritSection)
 
+/* ----------
+ * The max bytes for showing identifiers of MemoryContext.
+ * ----------
+ */
+#define MEMORY_CONTEXT_IDENT_DISPLAY_SIZE	1024
+
 /*****************************************************************************
  *	  EXPORTED ROUTINES														 *
  *****************************************************************************/
@@ -1220,3 +1228,133 @@ pchomp(const char *in)
 		n--;
 	return pnstrdup(in, n);
 }
+
+/*
+ * PutMemoryContextsStatsTupleStore
+ *		One recursion level for pg_get_backend_memory_contexts.
+ */
+static void
+PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
+								TupleDesc tupdesc, MemoryContext context,
+								const char *parent, int level)
+{
+#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS	9
+
+	Datum		values[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
+	bool		nulls[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
+	MemoryContextCounters stat;
+	MemoryContext child;
+	const char *name;
+	const char *ident;
+
+	AssertArg(MemoryContextIsValid(context));
+
+	name = context->name;
+	ident = context->ident;
+
+	/*
+	 * To be consistent with logging output, we label dynahash contexts
+	 * with just the hash table name as with MemoryContextStatsPrint().
+	 */
+	if (ident && strcmp(name, "dynahash") == 0)
+	{
+		name = ident;
+		ident = NULL;
+	}
+
+	/* Examine the context itself */
+	memset(&stat, 0, sizeof(stat));
+	(*context->methods->stats) (context, NULL, (void *) &level, &stat);
+
+	memset(values, 0, sizeof(values));
+	memset(nulls, 0, sizeof(nulls));
+
+	if (name)
+		values[0] = CStringGetTextDatum(name);
+	else
+		nulls[0] = true;
+
+	if (ident)
+	{
+		int		idlen = strlen(ident);
+		char		clipped_ident[MEMORY_CONTEXT_IDENT_DISPLAY_SIZE];
+
+		/*
+		 * Some identifiers such as SQL query string can be very long,
+		 * truncate oversize identifiers.
+		 */
+		if (idlen >= MEMORY_CONTEXT_IDENT_DISPLAY_SIZE)
+			idlen = pg_mbcliplen(ident, idlen, MEMORY_CONTEXT_IDENT_DISPLAY_SIZE - 1);
+
+		memcpy(clipped_ident, ident, idlen);
+		clipped_ident[idlen] = '\0';
+		values[1] = CStringGetTextDatum(clipped_ident);
+	}
+	else
+		nulls[1] = true;
+
+	if (parent)
+		values[2] = CStringGetTextDatum(parent);
+	else
+		nulls[2] = true;
+
+	values[3] = Int32GetDatum(level);
+	values[4] = Int64GetDatum(stat.totalspace);
+	values[5] = Int64GetDatum(stat.nblocks);
+	values[6] = Int64GetDatum(stat.freespace);
+	values[7] = Int64GetDatum(stat.freechunks);
+	values[8] = Int64GetDatum(stat.totalspace - stat.freespace);
+	tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+
+	for (child = context->firstchild; child != NULL; child = child->nextchild)
+	{
+		PutMemoryContextsStatsTupleStore(tupstore, tupdesc,
+								  child, name, level + 1);
+	}
+}
+
+/*
+ * pg_get_backend_memory_contexts
+ *		SQL SRF showing backend memory context.
+ */
+Datum
+pg_get_backend_memory_contexts(PG_FUNCTION_ARGS)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+
+	/* 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);
+
+	PutMemoryContextsStatsTupleStore(tupstore, tupdesc,
+								TopMemoryContext, NULL, 0);
+
+	/* clean up and return the tuplestore */
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 92849511219..3e677976300 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202007251
+#define CATALOG_VERSION_NO	202008191
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 082a11f2708..27989971db7 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7807,6 +7807,15 @@
   proargnames => '{name,off,size,allocated_size}',
   prosrc => 'pg_get_shmem_allocations' },
 
+# memory context of local backend
+{ oid => '2282', descr => 'information about all memory contexts of local backend',
+  proname => 'pg_get_backend_memory_contexts', prorows => '100', proretset => 't',
+  provolatile => 'v', proparallel => 'r', prorettype => 'record', proargtypes => '',
+  proallargtypes => '{text,text,text,int4,int8,int8,int8,int8,int8}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o}',
+  proargnames => '{name, ident, parent, level, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes}',
+  prosrc => 'pg_get_backend_memory_contexts' },
+
 # non-persistent series generator
 { oid => '1066', descr => 'non-persistent series generator',
   proname => 'generate_series', prorows => '1000',
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 601734a6f1e..2a18dc423e2 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1324,6 +1324,16 @@ pg_available_extensions| SELECT e.name,
     e.comment
    FROM (pg_available_extensions() e(name, default_version, comment)
      LEFT JOIN pg_extension x ON ((e.name = x.extname)));
+pg_backend_memory_contexts| SELECT pg_get_backend_memory_contexts.name,
+    pg_get_backend_memory_contexts.ident,
+    pg_get_backend_memory_contexts.parent,
+    pg_get_backend_memory_contexts.level,
+    pg_get_backend_memory_contexts.total_bytes,
+    pg_get_backend_memory_contexts.total_nblocks,
+    pg_get_backend_memory_contexts.free_bytes,
+    pg_get_backend_memory_contexts.free_chunks,
+    pg_get_backend_memory_contexts.used_bytes
+   FROM pg_get_backend_memory_contexts() pg_get_backend_memory_contexts(name, ident, parent, level, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes);
 pg_config| SELECT pg_config.name,
     pg_config.setting
    FROM pg_config() pg_config(name, setting);