Subject: [PATCH v9 2/4] Add checkpoint and redo LSN to LogCheckpointEnd log message

From: Bharath Rupireddy <[email-masked]>
Date: Tue, 1 Feb 2022 04:34:54 +0000

It is useful (for debugging purposes) if the checkpoint end message
has the checkpoint LSN(end) and REDO LSN(start). It gives more
context while analyzing checkpoint-related issues. The pg_controldata
gives the last checkpoint LSN and REDO LSN, but having this info
alongside the log message helps analyze issues that happened
previously, connect the dots and identify the root cause.
---
 src/backend/access/transam/xlog.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index a6c6e67f80..60da34433b 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8923,7 +8923,8 @@ LogCheckpointEnd(bool restartpoint)
 						"%d WAL file(s) added, %d removed, %d recycled; "
 						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
 						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
-						"distance=%d kB, estimate=%d kB",
+						"distance=%d kB, estimate=%d kB; "
+						"lsn=%X/%X, redo lsn=%X/%X",
 						CheckpointStats.ckpt_bufs_written,
 						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
 						CheckpointStats.ckpt_segs_added,
@@ -8936,14 +8937,18 @@ LogCheckpointEnd(bool restartpoint)
 						longest_msecs / 1000, (int) (longest_msecs % 1000),
 						average_msecs / 1000, (int) (average_msecs % 1000),
 						(int) (PrevCheckPointDistance / 1024.0),
-						(int) (CheckPointDistanceEstimate / 1024.0))));
+						(int) (CheckPointDistanceEstimate / 1024.0),
+						/* we are the only updator of these variables */
+						LSN_FORMAT_ARGS(ControlFile->checkPoint),
+						LSN_FORMAT_ARGS(ControlFile->checkPointCopy.redo))));
 	else
 		ereport(LOG,
 				(errmsg("checkpoint complete: wrote %d buffers (%.1f%%); "
 						"%d WAL file(s) added, %d removed, %d recycled; "
 						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
 						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
-						"distance=%d kB, estimate=%d kB",
+						"distance=%d kB, estimate=%d kB; "
+						"lsn=%X/%X, redo lsn=%X/%X",
 						CheckpointStats.ckpt_bufs_written,
 						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
 						CheckpointStats.ckpt_segs_added,
@@ -8956,7 +8961,10 @@ LogCheckpointEnd(bool restartpoint)
 						longest_msecs / 1000, (int) (longest_msecs % 1000),
 						average_msecs / 1000, (int) (average_msecs % 1000),
 						(int) (PrevCheckPointDistance / 1024.0),
-						(int) (CheckPointDistanceEstimate / 1024.0))));
+						(int) (CheckPointDistanceEstimate / 1024.0),
+						/* we are the only updator of these variables */
+						LSN_FORMAT_ARGS(ControlFile->checkPoint),
+						LSN_FORMAT_ARGS(ControlFile->checkPointCopy.redo))));
 }
 
 /*
-- 
2.27.0

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 filename="v9-0003-Change-location-to-lsn-in-pg_controldata.patch"