1 files changed, 75 insertions, 0 deletions

diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 41243d0187a..8288da5277f 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -29,6 +29,7 @@
 #include "postgres.h"
 
 #include "access/xact.h"
+#include "access/xlogutils.h"
 #include "access/xlog_internal.h"
 #include "fmgr.h"
 #include "miscadmin.h"
@@ -41,6 +42,7 @@
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "utils/builtins.h"
+#include "utils/inval.h"
 #include "utils/memutils.h"
 
 /* data for errcontext callback */
@@ -1949,3 +1951,76 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
 	rb->totalTxns = 0;
 	rb->totalBytes = 0;
 }
+
+/*
+ * Read up to the end of WAL starting from the decoding slot's restart_lsn.
+ * Return true if any meaningful/decodable WAL records are encountered,
+ * otherwise false.
+ */
+bool
+LogicalReplicationSlotHasPendingWal(XLogRecPtr end_of_wal)
+{
+	bool		has_pending_wal = false;
+
+	Assert(MyReplicationSlot);
+
+	PG_TRY();
+	{
+		LogicalDecodingContext *ctx;
+
+		/*
+		 * Create our decoding context in fast_forward mode, passing start_lsn
+		 * as InvalidXLogRecPtr, so that we start processing from the slot's
+		 * confirmed_flush.
+		 */
+		ctx = CreateDecodingContext(InvalidXLogRecPtr,
+									NIL,
+									true,	/* fast_forward */
+									XL_ROUTINE(.page_read = read_local_xlog_page,
+											   .segment_open = wal_segment_open,
+											   .segment_close = wal_segment_close),
+									NULL, NULL, NULL);
+
+		/*
+		 * Start reading at the slot's restart_lsn, which we know points to a
+		 * valid record.
+		 */
+		XLogBeginRead(ctx->reader, MyReplicationSlot->data.restart_lsn);
+
+		/* Invalidate non-timetravel entries */
+		InvalidateSystemCaches();
+
+		/* Loop until the end of WAL or some changes are processed */
+		while (!has_pending_wal && ctx->reader->EndRecPtr < end_of_wal)
+		{
+			XLogRecord *record;
+			char	   *errm = NULL;
+
+			record = XLogReadRecord(ctx->reader, &errm);
+
+			if (errm)
+				elog(ERROR, "could not find record for logical decoding: %s", errm);
+
+			if (record != NULL)
+				LogicalDecodingProcessRecord(ctx, ctx->reader);
+
+			has_pending_wal = ctx->processing_required;
+
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		/* Clean up */
+		FreeDecodingContext(ctx);
+		InvalidateSystemCaches();
+	}
+	PG_CATCH();
+	{
+		/* clear all timetravel entries */
+		InvalidateSystemCaches();
+
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+
+	return has_pending_wal;
+}