Show redo LSN in checkpoint logs

Hello.

Sometimes, I needed to infer where a past checkpoint make wal segments
unnecessary up to, or just to know the LSN at a past point in
time. But there's no convenient source for that.

The attached small patch enables me (or us) to do that by looking into
server log files.


> LOG:  checkpoint complete: wrote 3 buffers (0.0%); 0 WAL file(s) added, 0 removed, 0 recycled; write=0.008 s,
sync=0.035s, total=0.064 s; sync files=4, longest=0.017 s, average=0.009 s; distance=16420 kB, estimate=16420 kB,
redo=0/30091D8

Does that make sense?

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index e51a7a749d..b6d7013a73 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8761,7 +8761,7 @@ 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, redo=%X/%X",
                         CheckpointStats.ckpt_bufs_written,
                         (double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
                         CheckpointStats.ckpt_segs_added,
@@ -8774,14 +8774,15 @@ 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),
+                        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, redo=%X/%X",
                         CheckpointStats.ckpt_bufs_written,
                         (double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
                         CheckpointStats.ckpt_segs_added,
@@ -8794,7 +8795,8 @@ 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),
+                        LSN_FORMAT_ARGS(ControlFile->checkPointCopy.redo))));
 }
 
 /*