Skip empty transaction stream in test_decoding.

We were decoding empty transactions via streaming APIs added in commit
45fdc9738b even when the user used the option 'skip-empty-xacts'. The APIs
makes no effort to skip empty xacts under the assumption that we will
never try to stream such transactions. However, that is not true because
we can pick to stream a transaction that has change messages for
REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT and we don't send such messages to
downstream rather they are just to update the internal state. So, we need
to skip such xacts when plugin uses the option 'skip-empty-xacts'.

Diagnosed-By: Amit Kapila
Author: Dilip Kumar
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1+OqgFNZkf7=ETe_y5ntjgDk3T0wcdkd4Sot_u1hySGfw@mail.gmail.com

1 files changed, 37 insertions, 18 deletions

diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 34745150e9b..e60ab34a5a7 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -64,6 +64,10 @@ static void pg_decode_message(LogicalDecodingContext *ctx,
 							  Size sz, const char *message);
 static void pg_decode_stream_start(LogicalDecodingContext *ctx,
 								   ReorderBufferTXN *txn);
+static void pg_output_stream_start(LogicalDecodingContext *ctx,
+								   TestDecodingData *data,
+								   ReorderBufferTXN *txn,
+								   bool last_write);
 static void pg_decode_stream_stop(LogicalDecodingContext *ctx,
 								  ReorderBufferTXN *txn);
 static void pg_decode_stream_abort(LogicalDecodingContext *ctx,
@@ -583,34 +587,38 @@ pg_decode_message(LogicalDecodingContext *ctx,
 	OutputPluginWrite(ctx, true);
 }
 
-/*
- * We never try to stream any empty xact so we don't need any special handling
- * for skip_empty_xacts in streaming mode APIs.
- */
 static void
 pg_decode_stream_start(LogicalDecodingContext *ctx,
 					   ReorderBufferTXN *txn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
-	OutputPluginPrepareWrite(ctx, true);
+	data->xact_wrote_changes = false;
+	if (data->skip_empty_xacts)
+		return;
+	pg_output_stream_start(ctx, data, txn, true);
+}
+
+static void
+pg_output_stream_start(LogicalDecodingContext *ctx, TestDecodingData *data, ReorderBufferTXN *txn, bool last_write)
+{
+	OutputPluginPrepareWrite(ctx, last_write);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "opening a streamed block for transaction TXN %u", txn->xid);
 	else
 		appendStringInfo(ctx->out, "opening a streamed block for transaction");
-	OutputPluginWrite(ctx, true);
+	OutputPluginWrite(ctx, last_write);
 }
 
-/*
- * We never try to stream any empty xact so we don't need any special handling
- * for skip_empty_xacts in streaming mode APIs.
- */
 static void
 pg_decode_stream_stop(LogicalDecodingContext *ctx,
 					  ReorderBufferTXN *txn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+		return;
+
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "closing a streamed block for transaction TXN %u", txn->xid);
@@ -619,10 +627,6 @@ pg_decode_stream_stop(LogicalDecodingContext *ctx,
 	OutputPluginWrite(ctx, true);
 }
 
-/*
- * We never try to stream any empty xact so we don't need any special handling
- * for skip_empty_xacts in streaming mode APIs.
- */
 static void
 pg_decode_stream_abort(LogicalDecodingContext *ctx,
 					   ReorderBufferTXN *txn,
@@ -630,6 +634,9 @@ pg_decode_stream_abort(LogicalDecodingContext *ctx,
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+		return;
+
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "aborting streamed (sub)transaction TXN %u", txn->xid);
@@ -638,10 +645,6 @@ pg_decode_stream_abort(LogicalDecodingContext *ctx,
 	OutputPluginWrite(ctx, true);
 }
 
-/*
- * We never try to stream any empty xact so we don't need any special handling
- * for skip_empty_xacts in streaming mode APIs.
- */
 static void
 pg_decode_stream_commit(LogicalDecodingContext *ctx,
 						ReorderBufferTXN *txn,
@@ -649,6 +652,9 @@ pg_decode_stream_commit(LogicalDecodingContext *ctx,
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+		return;
+
 	OutputPluginPrepareWrite(ctx, true);
 
 	if (data->include_xids)
@@ -676,6 +682,13 @@ pg_decode_stream_change(LogicalDecodingContext *ctx,
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
+	/* output stream start if we haven't yet */
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	{
+		pg_output_stream_start(ctx, data, txn, false);
+	}
+	data->xact_wrote_changes = true;
+
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "streaming change for TXN %u", txn->xid);
@@ -722,6 +735,12 @@ pg_decode_stream_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	{
+		pg_output_stream_start(ctx, data, txn, false);
+	}
+	data->xact_wrote_changes = true;
+
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "streaming truncate for TXN %u", txn->xid);