v2-0001-Adding-id-parent_id-into-pg_backend_memory_contex.patch

From e9134ad5465d0dae626cf658def2ca58648d64c2 Mon Sep 17 00:00:00 2001
From: Melih Mutlu <m.melihmutlu@gmail.com>
Date: Tue, 13 Jun 2023 15:00:05 +0300
Subject: [PATCH v2] Adding id/parent_id into pg_backend_memory_contexts

Added three new fields into the tuples returned by
pg_get_backend_memory_contexts() to specify the parent/child relation
between memory contexts and the path from root to current context.

Context names cannot be relied on since they're not unique. Therefore,
unique id and parent_id are needed for each context. Those new id's are
assigned during pg_get_backend_memory_contexts() call and not stored
anywhere. So they may change in each pg_get_backend_memory_contexts()
call and shouldn't be used across differenct
pg_get_backend_memory_contexts() calls.

Context id's are start from 0 which is assigned to TopMemoryContext.
---
 doc/src/sgml/system-views.sgml      | 27 +++++++++++++
 src/backend/utils/adt/mcxtfuncs.c   | 59 ++++++++++++++++++++++++++---
 src/include/catalog/pg_proc.dat     |  6 +--
 src/test/regress/expected/rules.out |  7 +++-
 4 files changed, 89 insertions(+), 10 deletions(-)

diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index 57b228076e..7811130cfb 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -538,6 +538,33 @@
        Used space in bytes
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>context_id</structfield> <type>int4</type>
+      </para>
+      <para>
+       Current context id
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parent_id</structfield> <type>int4</type>
+      </para>
+      <para>
+       Parent context id
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>path</structfield> <type>int4</type>
+      </para>
+      <para>
+       Path to reach the current context from TopMemoryContext
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/utils/adt/mcxtfuncs.c b/src/backend/utils/adt/mcxtfuncs.c
index 92ca5b2f72..81cb35dd47 100644
--- a/src/backend/utils/adt/mcxtfuncs.c
+++ b/src/backend/utils/adt/mcxtfuncs.c
@@ -20,6 +20,7 @@
 #include "mb/pg_wchar.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
+#include "utils/array.h"
 #include "utils/builtins.h"
 
 /* ----------
@@ -28,6 +29,8 @@
  */
 #define MEMORY_CONTEXT_IDENT_DISPLAY_SIZE	1024
 
+static Datum convert_path_to_datum(List *path);
+
 /*
  * PutMemoryContextsStatsTupleStore
  *		One recursion level for pg_get_backend_memory_contexts.
@@ -35,9 +38,10 @@
 static void
 PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
 								 TupleDesc tupdesc, MemoryContext context,
-								 const char *parent, int level)
+								 const char *parent, int level, int *context_id,
+								 int parent_id, List *path)
 {
-#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS	9
+#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS	12
 
 	Datum		values[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
 	bool		nulls[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
@@ -45,6 +49,7 @@ PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
 	MemoryContext child;
 	const char *name;
 	const char *ident;
+	int  current_context_id = (*context_id)++;
 
 	Assert(MemoryContextIsValid(context));
 
@@ -103,13 +108,29 @@ PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
 	values[6] = Int64GetDatum(stat.freespace);
 	values[7] = Int64GetDatum(stat.freechunks);
 	values[8] = Int64GetDatum(stat.totalspace - stat.freespace);
+	values[9] = Int32GetDatum(current_context_id);
+
+	if(parent_id < 0)
+		/* TopMemoryContext has no parent context */
+		nulls[10] = true;
+	else
+		values[10] = Int32GetDatum(parent_id);
+
+	if (path == NIL)
+		nulls[11] = true;
+	else
+		values[11] = convert_path_to_datum(path);
+
 	tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 
+	path = lappend_int(path, current_context_id);
 	for (child = context->firstchild; child != NULL; child = child->nextchild)
 	{
-		PutMemoryContextsStatsTupleStore(tupstore, tupdesc,
-										 child, name, level + 1);
+		PutMemoryContextsStatsTupleStore(tupstore, tupdesc, child, name,
+										 level+1, context_id,
+										 current_context_id, path);
 	}
+	path = list_delete_last(path);
 }
 
 /*
@@ -120,10 +141,15 @@ Datum
 pg_get_backend_memory_contexts(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	int context_id = 0;
+	List *path = NIL;
+
+	elog(LOG, "pg_get_backend_memory_contexts called");
 
 	InitMaterializedSRF(fcinfo, 0);
 	PutMemoryContextsStatsTupleStore(rsinfo->setResult, rsinfo->setDesc,
-									 TopMemoryContext, NULL, 0);
+									 TopMemoryContext, NULL, 0, &context_id,
+									 -1, path);
 
 	return (Datum) 0;
 }
@@ -193,3 +219,26 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(true);
 }
+
+/*
+ * Convert a list of context ids to a int[] Datum
+ */
+static Datum
+convert_path_to_datum(List *path)
+{
+	Datum	   *datum_array;
+	int			length;
+	ArrayType  *result_array;
+	ListCell   *lc;
+
+	length = list_length(path);
+	datum_array = (Datum *) palloc(length * sizeof(Datum));
+	length = 0;
+	foreach(lc, path)
+	{
+		datum_array[length++] = Int32GetDatum((int) lfirst_int(lc));
+	}
+	result_array = construct_array_builtin(datum_array, length, INT4OID);
+
+	return PointerGetDatum(result_array);
+}
\ No newline at end of file
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 6996073989..49514ad792 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -8212,9 +8212,9 @@
   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}',
+  proallargtypes => '{text,text,text,int4,int8,int8,int8,int8,int8,int4,int4,_int4}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{name, ident, parent, level, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes, id, parent_id, path}',
   prosrc => 'pg_get_backend_memory_contexts' },
 
 # logging memory contexts of the specified backend
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index e07afcd4aa..c7112be09e 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1311,8 +1311,11 @@ pg_backend_memory_contexts| SELECT name,
     total_nblocks,
     free_bytes,
     free_chunks,
-    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);
+    used_bytes,
+    id,
+    parent_id,
+    path
+   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, id, parent_id, path);
 pg_config| SELECT name,
     setting
    FROM pg_config() pg_config(name, setting);
-- 
2.25.1