Add skip-empty-xacts option to test_decoding for use in the regression tests.

The regression tests for contrib/test_decoding regularly failed on
postgres instances that were very slow. Either because the hardware
itself was slow or because very expensive debugging options like
CLOBBER_CACHE_ALWAYS were used.

The reason they failed was just that some additional transactions were
decoded. Analyze and vacuum, triggered by autovac.

To fix just add a option to test_decoding to only display transactions
in which a change was actually displayed. That's not pretty because it
removes information from the tests; but better than constantly failing
tests in very likely harmless ways.

Backpatch to 9.4 where logical decoding was introduced.

Discussion: 20140629142511.GA26930@awork2.anarazel.de

1 files changed, 42 insertions, 3 deletions

diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 6edc5fcd47a..fdbd313cda5 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -41,6 +41,8 @@ typedef struct
 	MemoryContext context;
 	bool		include_xids;
 	bool		include_timestamp;
+	bool		skip_empty_xacts;
+	bool		xact_wrote_changes;
 } TestDecodingData;
 
 static void pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
@@ -48,6 +50,10 @@ static void pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *
 static void pg_decode_shutdown(LogicalDecodingContext *ctx);
 static void pg_decode_begin_txn(LogicalDecodingContext *ctx,
 					ReorderBufferTXN *txn);
+static void pg_output_begin(LogicalDecodingContext *ctx,
+							TestDecodingData *data,
+							ReorderBufferTXN *txn,
+							bool last_write);
 static void pg_decode_commit_txn(LogicalDecodingContext *ctx,
 					 ReorderBufferTXN *txn, XLogRecPtr commit_lsn);
 static void pg_decode_change(LogicalDecodingContext *ctx,
@@ -82,7 +88,7 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 	ListCell   *option;
 	TestDecodingData *data;
 
-	data = palloc(sizeof(TestDecodingData));
+	data = palloc0(sizeof(TestDecodingData));
 	data->context = AllocSetContextCreate(ctx->context,
 										  "text conversion context",
 										  ALLOCSET_DEFAULT_MINSIZE,
@@ -90,6 +96,7 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 										  ALLOCSET_DEFAULT_MAXSIZE);
 	data->include_xids = true;
 	data->include_timestamp = false;
+	data->skip_empty_xacts = false;
 
 	ctx->output_plugin_private = data;
 
@@ -137,6 +144,17 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 			if (force_binary)
 				opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
 		}
+		else if (strcmp(elem->defname, "skip-empty-xacts") == 0)
+		{
+
+			if (elem->arg == NULL)
+				data->skip_empty_xacts = true;
+			else if (!parse_bool(strVal(elem->arg), &data->skip_empty_xacts))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				  errmsg("could not parse value \"%s\" for parameter \"%s\"",
+						 strVal(elem->arg), elem->defname)));
+		}
 		else
 		{
 			ereport(ERROR,
@@ -164,12 +182,22 @@ pg_decode_begin_txn(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_begin(ctx, data, txn, true);
+}
+
+static void
+pg_output_begin(LogicalDecodingContext *ctx, TestDecodingData *data, ReorderBufferTXN *txn, bool last_write)
+{
+	OutputPluginPrepareWrite(ctx, last_write);
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "BEGIN %u", txn->xid);
 	else
 		appendStringInfoString(ctx->out, "BEGIN");
-	OutputPluginWrite(ctx, true);
+	OutputPluginWrite(ctx, last_write);
 }
 
 /* COMMIT callback */
@@ -179,6 +207,9 @@ pg_decode_commit_txn(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, "COMMIT %u", txn->xid);
@@ -338,6 +369,14 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 	MemoryContext old;
 
 	data = ctx->output_plugin_private;
+
+	/* output BEGIN if we haven't yet */
+	if (data->skip_empty_xacts && !data->xact_wrote_changes)
+	{
+		pg_output_begin(ctx, data, txn, false);
+	}
+	data->xact_wrote_changes = true;
+
 	class_form = RelationGetForm(relation);
 	tupdesc = RelationGetDescr(relation);