v17-0013-bufmgr-Return-whether-WaitReadBuffers-needed-to-.patch

From 2033801786bd7eaaa1320c772d38f06a12814b39 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Tue, 3 Mar 2026 16:50:50 -0500
Subject: [PATCH v17 13/18] bufmgr: Return whether WaitReadBuffers() needed to
 wait

In a subsequent commit read_stream.c will use this as an input to the read
ahead distance.

Author:
Reviewed-by:
Discussion: https://postgr.es/m/
Backpatch:
---
 src/include/storage/bufmgr.h        |  2 +-
 src/backend/storage/buffer/bufmgr.c | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 84933772e..bab57c2b5 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -250,7 +250,7 @@ extern bool StartReadBuffers(ReadBuffersOperation *operation,
 							 BlockNumber blockNum,
 							 int *nblocks,
 							 int flags);
-extern void WaitReadBuffers(ReadBuffersOperation *operation);
+extern bool WaitReadBuffers(ReadBuffersOperation *operation);
 
 extern void ReleaseBuffer(Buffer buffer);
 extern void UnlockReleaseBuffer(Buffer buffer);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index b7cbc416f..ae1e538dd 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1731,12 +1731,20 @@ ProcessReadBuffersResult(ReadBuffersOperation *operation)
 	Assert(operation->nblocks_done <= operation->nblocks);
 }
 
-void
+/*
+ * Wait for the IO operation initiated by StartReadBuffers() et al to
+ * complete.
+ *
+ * Returns whether the IO operation already had completed by the time of this
+ * call.
+ */
+bool
 WaitReadBuffers(ReadBuffersOperation *operation)
 {
 	PgAioReturn *aio_ret = &operation->io_return;
 	IOContext	io_context;
 	IOObject	io_object;
+	bool		needed_wait = false;
 
 	if (operation->persistence == RELPERSISTENCE_TEMP)
 	{
@@ -1798,6 +1806,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 				instr_time	io_start = pgstat_prepare_io_time(track_io_timing);
 
 				pgaio_wref_wait(&operation->io_wref);
+				needed_wait = true;
 
 				/*
 				 * The IO operation itself was already counted earlier, in
@@ -1850,6 +1859,12 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 
 		CHECK_FOR_INTERRUPTS();
 
+		/*
+		 * If the IO completed only partially, we need to perform additional
+		 * work, consider that a form of having had to wait.
+		 */
+		needed_wait = true;
+
 		/*
 		 * This may only complete the IO partially, either because some
 		 * buffers were already valid, or because of a partial read.
@@ -1866,6 +1881,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 	CheckReadBuffersOperation(operation, true);
 
 	/* NB: READ_DONE tracepoint was already executed in completion callback */
+	return needed_wait;
 }
 
 /*
-- 
2.53.0