Fix 'skip-empty-xacts' option in test_decoding for streaming mode.

In streaming mode, the transaction can be decoded in multiple streams and
those streams can be interleaved with streams of other transactions. So,
we can't remember the transaction's write status in the logical decoding
context because that might get changed due to some other transactions and
lead to wrong answers for 'skip-empty-xacts' option. We decided to keep
each transaction's write status in the ReorderBufferTxn to avoid
interleaved streams changing the status of some unrelated transactions.

Diagnosed-by: Amit Kapila
Author: Dilip Kumar
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1LR7=XNM_TLmpZMFuV8ZQpoxkem--NZJYf8YXmesbvwLA@mail.gmail.com

contrib/test_decoding/expected/concurrent_stream.out

-Parsed test spec with 2 sessions
+Parsed test spec with 3 sessions
 
-starting permutation: s0_begin s0_ddl s1_ddl s1_begin s1_toast_insert s1_commit s1_get_stream_changes
+starting permutation: s0_begin s0_ddl s1_ddl s1_begin s1_toast_insert s2_ddl s1_commit s1_get_stream_changes
 step s0_begin: BEGIN;
 step s0_ddl: CREATE TABLE stream_test1(data text);
 step s1_ddl: CREATE TABLE stream_test(data text);
 step s1_begin: BEGIN;
 step s1_toast_insert: INSERT INTO stream_test SELECT large_val();
+step s2_ddl: CREATE TABLE stream_test2(data text);
 step s1_commit: COMMIT;
 step s1_get_stream_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
 data           

contrib/test_decoding/specs/concurrent_stream.spec

@@ -23,9 +23,15 @@ setup { SET synchronous_commit=on; }
 step "s0_begin" { BEGIN; }
 step "s0_ddl"   {CREATE TABLE stream_test1(data text);}
 
+session "s2"
+setup { SET synchronous_commit=on; }
+step "s2_ddl"   {CREATE TABLE stream_test2(data text);}
+
 # The transaction commit for s1_ddl will add the INTERNAL_SNAPSHOT change to
 # the currently running s0_ddl and we want to test that s0_ddl should not get
-# streamed when user asked to skip-empty-xacts.
+# streamed when user asked to skip-empty-xacts. Similarly, the
+# INTERNAL_SNAPSHOT change added by s2_ddl should not change the results for
+# what gets streamed.
 session "s1"
 setup { SET synchronous_commit=on; }
 step "s1_ddl"   { CREATE TABLE stream_test(data text); }
@@ -34,4 +40,4 @@ step "s1_toast_insert" {INSERT INTO stream_test SELECT large_val();}
 step "s1_commit" { COMMIT; }
 step "s1_get_stream_changes" { SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');}
 
-permutation "s0_begin" "s0_ddl" "s1_ddl" "s1_begin" "s1_toast_insert" "s1_commit" "s1_get_stream_changes"
+permutation "s0_begin" "s0_ddl" "s1_ddl" "s1_begin" "s1_toast_insert" "s2_ddl" "s1_commit" "s1_get_stream_changes"

contrib/test_decoding/test_decoding.c

@@ -34,10 +34,24 @@ typedef struct
 	bool		include_xids;
 	bool		include_timestamp;
 	bool		skip_empty_xacts;
-	bool		xact_wrote_changes;
 	bool		only_local;
 } TestDecodingData;
 
+/*
+ * Maintain the per-transaction level variables to track whether the
+ * transaction and or streams have written any changes. In streaming mode the
+ * transaction can be decoded in streams so along with maintaining whether the
+ * transaction has written any changes, we also need to track whether the
+ * current stream has written any changes. This is required so that if user
+ * has requested to skip the empty transactions we can skip the empty streams
+ * even though the transaction has written some changes.
+ */
+typedef struct
+{
+	bool		xact_wrote_changes;
+	bool		stream_wrote_changes;
+} TestDecodingTxnData;
+
 static void pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 							  bool is_init);
 static void pg_decode_shutdown(LogicalDecodingContext *ctx);
@@ -255,8 +269,12 @@ static void
 pg_decode_begin_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata =
+	MemoryContextAllocZero(ctx->context, sizeof(TestDecodingTxnData));
+
+	txndata->xact_wrote_changes = false;
+	txn->output_plugin_private = txndata;
 
-	data->xact_wrote_changes = false;
 	if (data->skip_empty_xacts)
 		return;
 
@@ -280,8 +298,13 @@ pg_decode_commit_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 					 XLogRecPtr commit_lsn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
+	bool		xact_wrote_changes = txndata->xact_wrote_changes;
+
+	pfree(txndata);
+	txn->output_plugin_private = NULL;
 
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !xact_wrote_changes)
 		return;
 
 	OutputPluginPrepareWrite(ctx, true);
@@ -442,18 +465,20 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 				 Relation relation, ReorderBufferChange *change)
 {
 	TestDecodingData *data;
+	TestDecodingTxnData *txndata;
 	Form_pg_class class_form;
 	TupleDesc	tupdesc;
 	MemoryContext old;
 
 	data = ctx->output_plugin_private;
+	txndata = txn->output_plugin_private;
 
 	/* output BEGIN if we haven't yet */
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !txndata->xact_wrote_changes)
 	{
 		pg_output_begin(ctx, data, txn, false);
 	}
-	data->xact_wrote_changes = true;
+	txndata->xact_wrote_changes = true;
 
 	class_form = RelationGetForm(relation);
 	tupdesc = RelationGetDescr(relation);
@@ -527,17 +552,19 @@ pg_decode_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 				   int nrelations, Relation relations[], ReorderBufferChange *change)
 {
 	TestDecodingData *data;
+	TestDecodingTxnData *txndata;
 	MemoryContext old;
 	int			i;
 
 	data = ctx->output_plugin_private;
+	txndata = txn->output_plugin_private;
 
 	/* output BEGIN if we haven't yet */
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !txndata->xact_wrote_changes)
 	{
 		pg_output_begin(ctx, data, txn, false);
 	}
-	data->xact_wrote_changes = true;
+	txndata->xact_wrote_changes = true;
 
 	/* Avoid leaking memory by using and resetting our own context */
 	old = MemoryContextSwitchTo(data->context);
@@ -592,8 +619,20 @@ pg_decode_stream_start(LogicalDecodingContext *ctx,
 					   ReorderBufferTXN *txn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
 
-	data->xact_wrote_changes = false;
+	/*
+	 * Allocate the txn plugin data for the first stream in the transaction.
+	 */
+	if (txndata == NULL)
+	{
+		txndata =
+			MemoryContextAllocZero(ctx->context, sizeof(TestDecodingTxnData));
+		txndata->xact_wrote_changes = false;
+		txn->output_plugin_private = txndata;
+	}
+
+	txndata->stream_wrote_changes = false;
 	if (data->skip_empty_xacts)
 		return;
 	pg_output_stream_start(ctx, data, txn, true);
@@ -615,8 +654,9 @@ pg_decode_stream_stop(LogicalDecodingContext *ctx,
 					  ReorderBufferTXN *txn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
 
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !txndata->stream_wrote_changes)
 		return;
 
 	OutputPluginPrepareWrite(ctx, true);
@@ -634,7 +674,23 @@ pg_decode_stream_abort(LogicalDecodingContext *ctx,
 {
 	TestDecodingData *data = ctx->output_plugin_private;
 
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	/*
+	 * stream abort can be sent for an individual subtransaction but we
+	 * maintain the output_plugin_private only under the toptxn so if this is
+	 * not the toptxn then fetch the toptxn.
+	 */
+	ReorderBufferTXN *toptxn = txn->toptxn ? txn->toptxn : txn;
+	TestDecodingTxnData *txndata = toptxn->output_plugin_private;
+	bool		xact_wrote_changes = txndata->xact_wrote_changes;
+
+	if (txn->toptxn == NULL)
+	{
+		Assert(txn->output_plugin_private != NULL);
+		pfree(txndata);
+		txn->output_plugin_private = NULL;
+	}
+
+	if (data->skip_empty_xacts && !xact_wrote_changes)
 		return;
 
 	OutputPluginPrepareWrite(ctx, true);
@@ -651,8 +707,13 @@ pg_decode_stream_commit(LogicalDecodingContext *ctx,
 						XLogRecPtr commit_lsn)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
+	bool		xact_wrote_changes = txndata->xact_wrote_changes;
+
+	pfree(txndata);
+	txn->output_plugin_private = NULL;
 
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !xact_wrote_changes)
 		return;
 
 	OutputPluginPrepareWrite(ctx, true);
@@ -681,13 +742,14 @@ pg_decode_stream_change(LogicalDecodingContext *ctx,
 						ReorderBufferChange *change)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
 
 	/* output stream start if we haven't yet */
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !txndata->stream_wrote_changes)
 	{
 		pg_output_stream_start(ctx, data, txn, false);
 	}
-	data->xact_wrote_changes = true;
+	txndata->xact_wrote_changes = txndata->stream_wrote_changes = true;
 
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)
@@ -734,12 +796,13 @@ pg_decode_stream_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 						  ReorderBufferChange *change)
 {
 	TestDecodingData *data = ctx->output_plugin_private;
+	TestDecodingTxnData *txndata = txn->output_plugin_private;
 
-	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	if (data->skip_empty_xacts && !txndata->stream_wrote_changes)
 	{
 		pg_output_stream_start(ctx, data, txn, false);
 	}
-	data->xact_wrote_changes = true;
+	txndata->xact_wrote_changes = txndata->stream_wrote_changes = true;
 
 	OutputPluginPrepareWrite(ctx, true);
 	if (data->include_xids)

src/backend/replication/logical/reorderbuffer.c

@@ -402,6 +402,7 @@ ReorderBufferGetTXN(ReorderBuffer *rb)
 
 	/* InvalidCommandId is not zero, so set it explicitly */
 	txn->command_id = InvalidCommandId;
+	txn->output_plugin_private = NULL;
 
 	return txn;
 }

src/include/replication/reorderbuffer.h

@@ -378,6 +378,11 @@ typedef struct ReorderBufferTXN
 
 	/* If we have detected concurrent abort then ignore future changes. */
 	bool		concurrent_abort;
+
+	/*
+	 * Private data pointer of the output plugin.
+	 */
+	void	   *output_plugin_private;
 } ReorderBufferTXN;
 
 /* so we can define the callbacks used inside struct ReorderBuffer itself */

src/tools/pgindent/typedefs.list

@@ -2505,6 +2505,7 @@ Tcl_Obj
 Tcl_Time
 TempNamespaceStatus
 TestDecodingData
+TestDecodingTxnData
 TestSpec
 TextFreq
 TextPositionState