Fix an uninitialized access in hash_xlog_squeeze_page().

Commit 861f86beea changed hash_xlog_squeeze_page() to start reading
the write buffer conditionally but forgot to initialize it leading to an
uninitialized access.

Reported-by: Alexander Lakhin
Author: Hayato Kuroda
Reviewed-by: Alexander Lakhin, Amit Kapila
Discussion: http://postgr.es/m/62ed1a9f-746a-8e86-904b-51b9b806a1d9@gmail.com

meson.build

@@ -2924,8 +2924,12 @@ potentially_conflicting_files = []
 foreach t : potentially_conflicting_files_t
   potentially_conflicting_files += t.full_path()
 endforeach
-foreach t : configure_files
-  t = '@0@'.format(t)
+foreach t1 : configure_files
+  if meson.version().version_compare('>=0.59')
+    t = fs.parent(t1) / fs.name(t1)
+  else
+    t = '@0@'.format(t1)
+  endif
   potentially_conflicting_files += meson.current_build_dir() / t
 endforeach
 foreach sub, fnames : generated_sources_ac

src/backend/access/hash/hash_xlog.c

@@ -632,7 +632,7 @@ hash_xlog_squeeze_page(XLogReaderState *record)
 	XLogRecPtr	lsn = record->EndRecPtr;
 	xl_hash_squeeze_page *xldata = (xl_hash_squeeze_page *) XLogRecGetData(record);
 	Buffer		bucketbuf = InvalidBuffer;
-	Buffer		writebuf;
+	Buffer		writebuf = InvalidBuffer;
 	Buffer		ovflbuf;
 	Buffer		prevbuf = InvalidBuffer;
 	Buffer		mapbuf;

src/backend/storage/lmgr/proc.c

@@ -614,6 +614,13 @@ InitAuxiliaryProcess(void)
 	 * Arrange to clean up at process exit.
 	 */
 	on_shmem_exit(AuxiliaryProcKill, Int32GetDatum(proctype));
+
+	/*
+	 * Now that we have a PGPROC, we could try to acquire lightweight locks.
+	 * Initialize local state needed for them.  (Heavyweight locks cannot be
+	 * acquired in aux processes.)
+	 */
+	InitLWLockAccess();
 }
 
 /*

src/backend/utils/init/miscinit.c

@@ -107,9 +107,8 @@ InitPostmasterChild(void)
 
 	/*
 	 * Set reference point for stack-depth checking.  This might seem
-	 * redundant in !EXEC_BACKEND builds; but it's not because the postmaster
-	 * launches its children from signal handlers, so we might be running on
-	 * an alternative stack.
+	 * redundant in !EXEC_BACKEND builds, but it's better to keep the depth
+	 * logic the same with and without that build option.
 	 */
 	(void) set_stack_base();
 

src/test/regress/expected/hash_index.out

@@ -298,6 +298,20 @@ ROLLBACK;
 INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 500) as i;
 CHECKPOINT;
 VACUUM hash_cleanup_heap;
+TRUNCATE hash_cleanup_heap;
+-- Insert tuples to both the primary bucket page and overflow pages.
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 500) as i;
+-- Fill overflow pages by "dead" tuples.
+BEGIN;
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 1500) as i;
+ROLLBACK;
+-- And insert some tuples again. During squeeze operation, these will be moved
+-- to other overflow pages and also allow overflow pages filled by dead tuples
+-- to be freed. Note the main purpose of this test is to test the case where
+-- we don't need to move any tuple from the overflow page being freed.
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 50) as i;
+CHECKPOINT;
+VACUUM hash_cleanup_heap;
 -- Clean up.
 DROP TABLE hash_cleanup_heap;
 -- Index on temp table.

src/test/regress/sql/hash_index.sql

@@ -284,6 +284,23 @@ INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 500) as i;
 CHECKPOINT;
 VACUUM hash_cleanup_heap;
 
+TRUNCATE hash_cleanup_heap;
+
+-- Insert tuples to both the primary bucket page and overflow pages.
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 500) as i;
+-- Fill overflow pages by "dead" tuples.
+BEGIN;
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 1500) as i;
+ROLLBACK;
+-- And insert some tuples again. During squeeze operation, these will be moved
+-- to other overflow pages and also allow overflow pages filled by dead tuples
+-- to be freed. Note the main purpose of this test is to test the case where
+-- we don't need to move any tuple from the overflow page being freed.
+INSERT INTO hash_cleanup_heap SELECT 1 FROM generate_series(1, 50) as i;
+
+CHECKPOINT;
+VACUUM hash_cleanup_heap;
+
 -- Clean up.
 DROP TABLE hash_cleanup_heap;