postgres.git / summary / log / commit / refs

commit    5cfbff48a4fdd1437ff06fcebdc2dade477ed4b8
Author:   Alexander Korotkov <akorotkov@postgresql.org>
Date:     Thu Aug 07 11:29:02 2025 +0000
First released in: 13.22, 14.19, 15.14, 16.10, 17.6, 18.0

    Fix checkpointer shared memory allocation
    
    Use Min(NBuffers, MAX_CHECKPOINT_REQUESTS) instead of NBuffers in
    CheckpointerShmemSize() to match the actual array size limit set in
    CheckpointerShmemInit().  This prevents wasting shared memory when
    NBuffers > MAX_CHECKPOINT_REQUESTS.  Also, fix the comment.
    
    Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
    Discussion: https://postgr.es/m/1439188.1754506714%40sss.pgh.pa.us
    Author: Xuneng Zhou <xunengzhou@gmail.com>
    Co-authored-by: Alexander Korotkov <aekorotkov@gmail.com>


 src/backend/postmaster/checkpointer.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 903d83e7dea..3914ac8da26 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -940,11 +940,14 @@ CheckpointerShmemSize(void)
 	Size		size;
 
 	/*
-	 * Currently, the size of the requests[] array is arbitrarily set equal to
-	 * NBuffers.  This may prove too large or small ...
+	 * The size of the requests[] array is arbitrarily set equal to NBuffers.
+	 * But there is a cap of MAX_CHECKPOINT_REQUESTS to prevent accumulating
+	 * too many checkpoint requests in the ring buffer.
 	 */
 	size = offsetof(CheckpointerShmemStruct, requests);
-	size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
+	size = add_size(size, mul_size(Min(NBuffers,
+									   MAX_CHECKPOINT_REQUESTS),
+								   sizeof(CheckpointerRequest)));
 
 	return size;
 }


[parent: 2ae8280d16c9]