After any checkpoint, close all smgr files handles in bgwriter

Author: simonat2ndQuadrant

src/backend/postmaster/bgwriter.c

@@ -276,6 +276,15 @@ BackgroundWriterMain(void)
 		 */
 		pgstat_send_bgwriter();
 
+		if (FirstCallSinceLastCheckpoint())
+		{
+			/*
+			 * After any checkpoint, close all smgr files.	This is so we
+			 * won't hang onto smgr references to deleted files indefinitely.
+			 */
+			smgrcloseall();
+		}
+
 		/*
 		 * Sleep until we are signaled or BgWriterDelay has elapsed.
 		 *

src/backend/postmaster/checkpointer.c

@@ -1346,3 +1346,28 @@ UpdateSharedMemoryConfig(void)
 
 	elog(DEBUG2, "checkpointer updated shared memory configuration values");
 }
+
+/*
+ * FirstCallSinceLastCheckpoint allows a process to take an action once
+ * per checkpoint cycle by asynchronously checking for checkpoint completion.
+ */
+bool
+FirstCallSinceLastCheckpoint(void)
+{
+	/* use volatile pointer to prevent code rearrangement */
+	volatile CheckpointerShmemStruct *cps = CheckpointerShmem;
+	static int 	ckpt_done = 0;
+	int 		new_done;
+	bool 		FirstCall = false;
+
+	SpinLockAcquire(&cps->ckpt_lck);
+	new_done = cps->ckpt_done;
+	SpinLockRelease(&cps->ckpt_lck);
+
+	if (new_done != ckpt_done)
+		FirstCall = true;
+
+	ckpt_done = new_done;
+
+	return FirstCall;
+}

src/include/postmaster/bgwriter.h

@@ -38,4 +38,6 @@ extern void AbsorbFsyncRequests(void);
 extern Size CheckpointerShmemSize(void);
 extern void CheckpointerShmemInit(void);
 
+extern bool FirstCallSinceLastCheckpoint(void);
+
 #endif   /* _BGWRITER_H */