Allow walreceiver configuration to change on reload

The parameters primary_conninfo, primary_slot_name and
wal_receiver_create_temp_slot can now be changed with a simple "reload"
signal, no longer requiring a server restart.  This is achieved by
signalling the walreceiver process to terminate and having it start
again with the new values.

Thanks to Andres Freund, Kyotaro Horiguchi, Fujii Masao for discussion.

Author: Sergei Kornilov <sk@zsrv.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/19513901543181143@sas1-19a94364928d.qloud-c.yandex.net

1 files changed, 89 insertions, 47 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index c7d93d37351..8fe92962b0d 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -816,9 +816,13 @@ static XLogSource readSource = XLOG_FROM_ANY;
  * currently have a WAL file open. If lastSourceFailed is set, our last
  * attempt to read from currentSource failed, and we should try another source
  * next.
+ *
+ * pendingWalRcvRestart is set when a config change occurs that requires a
+ * walreceiver restart.  This is only valid in XLOG_FROM_STREAM state.
  */
 static XLogSource currentSource = XLOG_FROM_ANY;
 static bool lastSourceFailed = false;
+static bool pendingWalRcvRestart = false;
 
 typedef struct XLogPageReadPrivate
 {
@@ -11905,6 +11909,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 	for (;;)
 	{
 		XLogSource	oldSource = currentSource;
+		bool		startWalReceiver = false;
 
 		/*
 		 * First check if we failed to read from the current source, and
@@ -11939,54 +11944,11 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 						return false;
 
 					/*
-					 * If primary_conninfo is set, launch walreceiver to try
-					 * to stream the missing WAL.
-					 *
-					 * If fetching_ckpt is true, RecPtr points to the initial
-					 * checkpoint location. In that case, we use RedoStartLSN
-					 * as the streaming start position instead of RecPtr, so
-					 * that when we later jump backwards to start redo at
-					 * RedoStartLSN, we will have the logs streamed already.
-					 */
-					if (PrimaryConnInfo && strcmp(PrimaryConnInfo, "") != 0)
-					{
-						XLogRecPtr	ptr;
-						TimeLineID	tli;
-
-						if (fetching_ckpt)
-						{
-							ptr = RedoStartLSN;
-							tli = ControlFile->checkPointCopy.ThisTimeLineID;
-						}
-						else
-						{
-							ptr = RecPtr;
-
-							/*
-							 * Use the record begin position to determine the
-							 * TLI, rather than the position we're reading.
-							 */
-							tli = tliOfPointInHistory(tliRecPtr, expectedTLEs);
-
-							if (curFileTLI > 0 && tli < curFileTLI)
-								elog(ERROR, "according to history file, WAL location %X/%X belongs to timeline %u, but previous recovered WAL file came from timeline %u",
-									 (uint32) (tliRecPtr >> 32),
-									 (uint32) tliRecPtr,
-									 tli, curFileTLI);
-						}
-						curFileTLI = tli;
-						RequestXLogStreaming(tli, ptr, PrimaryConnInfo,
-											 PrimarySlotName,
-											 wal_receiver_create_temp_slot);
-						receivedUpto = 0;
-					}
-
-					/*
-					 * Move to XLOG_FROM_STREAM state in either case. We'll
-					 * get immediate failure if we didn't launch walreceiver,
-					 * and move on to the next state.
+					 * Move to XLOG_FROM_STREAM state, and set to start a
+					 * walreceiver if necessary.
 					 */
 					currentSource = XLOG_FROM_STREAM;
+					startWalReceiver = true;
 					break;
 
 				case XLOG_FROM_STREAM:
@@ -12138,7 +12100,71 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 					Assert(StandbyMode);
 
 					/*
-					 * Check if WAL receiver is still active.
+					 * First, shutdown walreceiver if its restart has been
+					 * requested -- but no point if we're already slated for
+					 * starting it.
+					 */
+					if (pendingWalRcvRestart && !startWalReceiver)
+					{
+						ShutdownWalRcv();
+
+						/*
+						 * Re-scan for possible new timelines if we were
+						 * requested to recover to the latest timeline.
+						 */
+						if (recoveryTargetTimeLineGoal ==
+							RECOVERY_TARGET_TIMELINE_LATEST)
+							rescanLatestTimeLine();
+
+						startWalReceiver = true;
+					}
+					pendingWalRcvRestart = false;
+
+					/*
+					 * Launch walreceiver if needed.
+					 *
+					 * If fetching_ckpt is true, RecPtr points to the initial
+					 * checkpoint location. In that case, we use RedoStartLSN
+					 * as the streaming start position instead of RecPtr, so
+					 * that when we later jump backwards to start redo at
+					 * RedoStartLSN, we will have the logs streamed already.
+					 */
+					if (startWalReceiver &&
+						PrimaryConnInfo && strcmp(PrimaryConnInfo, "") != 0)
+					{
+						XLogRecPtr	ptr;
+						TimeLineID	tli;
+
+						if (fetching_ckpt)
+						{
+							ptr = RedoStartLSN;
+							tli = ControlFile->checkPointCopy.ThisTimeLineID;
+						}
+						else
+						{
+							ptr = RecPtr;
+
+							/*
+							 * Use the record begin position to determine the
+							 * TLI, rather than the position we're reading.
+							 */
+							tli = tliOfPointInHistory(tliRecPtr, expectedTLEs);
+
+							if (curFileTLI > 0 && tli < curFileTLI)
+								elog(ERROR, "according to history file, WAL location %X/%X belongs to timeline %u, but previous recovered WAL file came from timeline %u",
+									 (uint32) (tliRecPtr >> 32),
+									 (uint32) tliRecPtr,
+									 tli, curFileTLI);
+						}
+						curFileTLI = tli;
+						RequestXLogStreaming(tli, ptr, PrimaryConnInfo,
+											 PrimarySlotName,
+											 wal_receiver_create_temp_slot);
+						receivedUpto = 0;
+					}
+
+					/*
+					 * Check if WAL receiver is active or wait to start up.
 					 */
 					if (!WalRcvStreaming())
 					{
@@ -12267,6 +12293,22 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 }
 
 /*
+ * Set flag to signal the walreceiver to restart.  (The startup process calls
+ * this on noticing a relevant configuration change.)
+ */
+void
+StartupRequestWalReceiverRestart(void)
+{
+	if (currentSource == XLOG_FROM_STREAM && WalRcvRunning())
+	{
+		ereport(LOG,
+				(errmsg("wal receiver process shutdown requested")));
+
+		pendingWalRcvRestart = true;
+	}
+}
+
+/*
  * Determine what log level should be used to report a corrupt WAL record
  * in the current WAL page, previously read by XLogPageRead().
  *