stop calling pg_decode_caughtup callback in non-recovery scenarios

Author: kelvich

multimaster.c

@@ -191,7 +191,7 @@ HTAB* MtmGid2State;
 static HTAB* MtmRemoteFunctions;
 static HTAB* MtmLocalTables;
 
-static bool MtmIsRecoverySession;
+bool MtmIsRecoverySession;
 
 static MtmCurrentTrans MtmTx;
 static dlist_head MtmLsnMapping = DLIST_STATIC_INIT(MtmLsnMapping);

multimaster.h

@@ -393,6 +393,7 @@ extern bool MtmMajorNode;
 extern bool MtmBackgroundWorker;
 extern char* MtmRefereeConnStr;
 extern bool  MtmEnforceLocalTx;
+extern bool MtmIsRecoverySession;
 
 
 extern void  MtmArbiterInitialize(void);

pglogical_output.c

@@ -441,7 +441,17 @@ pg_decode_caughtup(LogicalDecodingContext *ctx)
 {
 	PGLogicalOutputData* data = (PGLogicalOutputData*)ctx->output_plugin_private;
 
-	if (data->api) { 
+	/*
+	 * MtmOutputPluginPrepareWrite send some bytes to downstream,
+	 * so we must avoid calling it in normal (non-recovery) situation.
+	 *
+	 * It's dirty hack to use MtmIsRecoverySession here and better to
+	 * provide also filter-like callback, but we plan to migrate to native
+	 * output plugin, so this code should anyway go away during next
+	 * release.
+	 */
+	if (data->api && MtmIsRecoverySession)
+	{
 		MtmOutputPluginPrepareWrite(ctx, true, true);
 		data->api->write_caughtup(ctx->out, data, ctx->reader->EndRecPtr);
 		MtmOutputPluginWrite(ctx, true, true);