Fix tracking of temp table relation extensions as writes

Karina figured out that I (Andres) confused BufferUsage.temp_blks_written with
BufferUsage.local_blks_written in fcdda1e4b5.

Tests in core PG can't easily test this, as BufferUsage is just used for
EXPLAIN (ANALYZE, BUFFERS) and pg_stat_statements. Thus this commit adds tests
for this to pg_stat_statements.

Reported-by: Karina Litskevich <litskevichkarina@gmail.com>
Author: Karina Litskevich <litskevichkarina@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CACiT8ibxXA6+0amGikbeFhm8B84XdQVo6D0Qfd1pQ1s8zpsnxQ@mail.gmail.com
Backpatch: 16-, where fcdda1e4b5 was merged

contrib/pg_stat_statements/expected/dml.out

@@ -139,6 +139,33 @@ SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
      1 |    1 | SELECT pg_stat_statements_reset()
 (10 rows)
 
+-- check that [temp] table relation extensions are tracked as writes
+CREATE TABLE pgss_extend_tab (a int, b text);
+CREATE TEMP TABLE pgss_extend_temp_tab (a int, b text);
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+INSERT INTO pgss_extend_tab (a, b) SELECT generate_series(1, 1000), 'something';
+INSERT INTO pgss_extend_temp_tab (a, b) SELECT generate_series(1, 1000), 'something';
+WITH sizes AS (
+  SELECT
+    pg_relation_size('pgss_extend_tab') / current_setting('block_size')::int8 AS rel_size,
+    pg_relation_size('pgss_extend_temp_tab') / current_setting('block_size')::int8 AS temp_rel_size
+)
+SELECT
+    SUM(local_blks_written) >= (SELECT temp_rel_size FROM sizes) AS temp_written_ok,
+    SUM(local_blks_dirtied) >= (SELECT temp_rel_size FROM sizes) AS temp_dirtied_ok,
+    SUM(shared_blks_written) >= (SELECT rel_size FROM sizes) AS written_ok,
+    SUM(shared_blks_dirtied) >= (SELECT rel_size FROM sizes) AS dirtied_ok
+FROM pg_stat_statements;
+ temp_written_ok | temp_dirtied_ok | written_ok | dirtied_ok 
+-----------------+-----------------+------------+------------
+ t               | t               | t          | t
+(1 row)
+
 SELECT pg_stat_statements_reset();
  pg_stat_statements_reset 
 --------------------------

contrib/pg_stat_statements/sql/dml.sql

@@ -73,4 +73,23 @@ MERGE INTO pgss_dml_tab USING pgss_dml_tab st ON (st.a = pgss_dml_tab.a AND st.a
 DROP TABLE pgss_dml_tab;
 
 SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- check that [temp] table relation extensions are tracked as writes
+CREATE TABLE pgss_extend_tab (a int, b text);
+CREATE TEMP TABLE pgss_extend_temp_tab (a int, b text);
+SELECT pg_stat_statements_reset();
+INSERT INTO pgss_extend_tab (a, b) SELECT generate_series(1, 1000), 'something';
+INSERT INTO pgss_extend_temp_tab (a, b) SELECT generate_series(1, 1000), 'something';
+WITH sizes AS (
+  SELECT
+    pg_relation_size('pgss_extend_tab') / current_setting('block_size')::int8 AS rel_size,
+    pg_relation_size('pgss_extend_temp_tab') / current_setting('block_size')::int8 AS temp_rel_size
+)
+SELECT
+    SUM(local_blks_written) >= (SELECT temp_rel_size FROM sizes) AS temp_written_ok,
+    SUM(local_blks_dirtied) >= (SELECT temp_rel_size FROM sizes) AS temp_dirtied_ok,
+    SUM(shared_blks_written) >= (SELECT rel_size FROM sizes) AS written_ok,
+    SUM(shared_blks_dirtied) >= (SELECT rel_size FROM sizes) AS dirtied_ok
+FROM pg_stat_statements;
+
 SELECT pg_stat_statements_reset();

src/backend/storage/buffer/localbuf.c

@@ -431,7 +431,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 
 	*extended_by = extend_by;
 
-	pgBufferUsage.temp_blks_written += extend_by;
+	pgBufferUsage.local_blks_written += extend_by;
 
 	return first_block;
 }