[PGPRO-4074] Port LogicalDecodingCaughtUp callback.

tags: multimaster
(cherry picked from commit d75ea7f66dfea0644d0bf98011f4bc2fd32bcd63)

Author: arssher

src/backend/replication/logical/logical.c

@@ -1040,6 +1040,35 @@ message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 	error_context_stack = errcallback.previous;
 }
 
+void LogicalDecodingCaughtUp(LogicalDecodingContext *ctx)
+{
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.caughtup_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "caughtup";
+	state.report_location = ctx->reader->EndRecPtr;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = InvalidTransactionId;
+	ctx->write_location = ctx->reader->EndRecPtr;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.caughtup_cb(ctx);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.

src/backend/replication/walsender.c

@@ -1380,6 +1380,7 @@ WalSndWaitForWal(XLogRecPtr loc)
 {
 	int			wakeEvents;
 	static XLogRecPtr RecentFlushPtr = InvalidXLogRecPtr;
+	bool		caughtup_cb_called = false;
 
 	/*
 	 * Fast path to avoid acquiring the spinlock in case we already know we
@@ -1459,6 +1460,15 @@ WalSndWaitForWal(XLogRecPtr loc)
 
 		/* Waiting for new WAL. Since we need to wait, we're now caught up. */
 		WalSndCaughtUp = true;
+		/*
+		 * Call cb only once: if it writes anyting, it'll probably call
+		 * WalSndWriteData who sets latch, thus creating busy loop.
+		 */
+		if (!caughtup_cb_called && logical_decoding_ctx)
+		{
+			LogicalDecodingCaughtUp(logical_decoding_ctx);
+			caughtup_cb_called = true;
+		}
 
 		/*
 		 * Try to flush any pending output to the client.

src/include/replication/logical.h

@@ -120,6 +120,8 @@ extern void LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn,
 												  XLogRecPtr restart_lsn);
 extern void LogicalConfirmReceivedLocation(XLogRecPtr lsn);
 
+extern void LogicalDecodingCaughtUp(LogicalDecodingContext *ctx);
+
 extern bool filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id);
 
 #endif

src/include/replication/output_plugin.h

@@ -139,6 +139,11 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (struct LogicalDecodingContext *ct
  */
 typedef void (*LogicalDecodeShutdownCB) (struct LogicalDecodingContext *ctx);
 
+/*
+ * Called when WAL sender caught up.
+ */
+typedef void (*LogicalDecodeCaughtUpCB) (struct LogicalDecodingContext * ctx);
+
 /*
  * Output plugin callbacks
  */
@@ -157,6 +162,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeAbortPreparedCB abort_prepared_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
+	LogicalDecodeCaughtUpCB caughtup_cb;
 } OutputPluginCallbacks;
 
 /* Functions in replication/logical/logical.c */