From cf41f56ba0d8c7f3bf92242020f742f201cf08d6 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Tue, 18 Nov 2025 14:24:12 -0500
Subject: [PATCH] resume

---
 src/backend/storage/aio/read_stream.c | 19 +++++++++++++++++++
 src/include/storage/read_stream.h     |  1 +
 2 files changed, 20 insertions(+)

diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c
index 031fde9f4cb..75bf92dc683 100644
--- a/src/backend/storage/aio/read_stream.c
+++ b/src/backend/storage/aio/read_stream.c
@@ -100,6 +100,7 @@ struct ReadStream
 	int16		pinned_buffers;
 	int16		distance;
 	int16		initialized_buffers;
+	int16		resume_distance;
 	int			read_buffers_flags;
 	bool		sync_mode;		/* using io_method=sync */
 	bool		batch_mode;		/* READ_STREAM_USE_BATCHING */
@@ -464,6 +465,7 @@ read_stream_look_ahead(ReadStream *stream)
 		if (blocknum == InvalidBlockNumber)
 		{
 			/* End of stream. */
+			stream->resume_distance = stream->distance;
 			stream->distance = 0;
 			break;
 		}
@@ -711,6 +713,7 @@ read_stream_begin_impl(int flags,
 		stream->distance = Min(max_pinned_buffers, stream->io_combine_limit);
 	else
 		stream->distance = 1;
+	stream->resume_distance = stream->distance;
 
 	/*
 	 * Since we always access the same relation, we can initialize parts of
@@ -862,6 +865,7 @@ read_stream_next_buffer(ReadStream *stream, void **per_buffer_data)
 		else
 		{
 			/* No more blocks, end of stream. */
+			stream->resume_distance = stream->distance;
 			stream->distance = 0;
 			stream->oldest_buffer_index = stream->next_buffer_index;
 			stream->pinned_buffers = 0;
@@ -1034,6 +1038,19 @@ read_stream_next_block(ReadStream *stream, BufferAccessStrategy *strategy)
 	return read_stream_get_block(stream, NULL);
 }
 
+/*
+ * Resume looking ahead after the block number callback reported end-of-stream.
+ * This is useful for streams of self-referential blocks, after a buffer needed
+ * to be consumed and examined to find more block numbers.
+ */
+void
+read_stream_resume(ReadStream *stream)
+{
+	if (stream->pinned_buffers > 0)
+		elog(ERROR, "read stream must be exhausted before resuming");
+	stream->distance = stream->resume_distance;
+}
+
 /*
  * Reset a read stream by releasing any queued up buffers, allowing the stream
  * to be used again for different blocks.  This can be used to clear an
@@ -1047,6 +1064,8 @@ read_stream_reset(ReadStream *stream)
 	Buffer		buffer;
 
 	/* Stop looking ahead. */
+	if (stream->distance > 0)
+		stream->resume_distance = stream->distance;
 	stream->distance = 0;
 
 	/* Forget buffered block number and fast path state. */
diff --git a/src/include/storage/read_stream.h b/src/include/storage/read_stream.h
index 9b0d65161d0..e29ac50fc9e 100644
--- a/src/include/storage/read_stream.h
+++ b/src/include/storage/read_stream.h
@@ -99,6 +99,7 @@ extern ReadStream *read_stream_begin_smgr_relation(int flags,
 												   ReadStreamBlockNumberCB callback,
 												   void *callback_private_data,
 												   size_t per_buffer_data_size);
+extern void read_stream_resume(ReadStream *stream);
 extern void read_stream_reset(ReadStream *stream);
 extern void read_stream_end(ReadStream *stream);
 
-- 
2.47.3