Re: Add checkpoint and redo LSN to LogCheckpointEnd log message

On Thu, Jan 20, 2022 at 8:30 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Thu, 20 Jan 2022 00:36:32 +0000, "Bossart, Nathan" <bossartn(at)amazon(dot)com> wrote in
> > On 1/3/22, 5:52 PM, "Kyotaro Horiguchi" <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> > > It seems to me "LSN" or just "location" is more confusing or
> > > mysterious than "REDO LSN" for the average user. If we want to avoid
> > > being technically too detailed, we would use just "start LSN=%X/%X,
> > > end LSN=%X/%X". And it is equivalent to "WAL range=[%X/%X, %X/%X]"..
> >
> > My first instinct was that this should stay aligned with
> > pg_controldata, but that would mean using "location=%X/%X, REDO
> > location=%X/%X," which doesn't seem terribly descriptive. IIUC the
> > "checkpoint location" is the LSN of the WAL record for the checkpoint,
> > and the "checkpoint's REDO location" is the LSN where checkpoint
> > creation began (i.e., what you must retain for crash recovery). My
> > vote is for "start=%X/%X, end=%X/%X."
>
> +1. Works for me. %X/%X itself expresses it is an LSN.

Thanks for the review. Here's the v4 patch, please have a look.

Let's not attempt to change how pg_controldata (tool and core
functions) emit the start and end LSN as checkpoint_lsn/redo_lsn and
checkpoint location/checkpoint's REDO location.

[1]
2022-01-28 03:06:10.213 UTC [2409486] LOG: checkpoint starting:
immediate force wait
2022-01-28 03:06:10.257 UTC [2409486] LOG: checkpoint complete:
start=0/14D9510, end=0/14D9548; wrote 4 buffers (0.0%); 0 WAL file(s)
added, 0 removed, 0 recycled; write=0.007 s, sync=0.008 s, total=0.044
s; sync files=3, longest=0.005 s, average=0.003 s; distance=0 kB,
estimate=0 kB

2022-01-28 03:06:42.254 UTC [2409486] LOG: checkpoint starting:
immediate force wait
2022-01-28 03:06:42.279 UTC [2409486] LOG: checkpoint complete:
start=0/14DBDB8, end=0/14DBDF0; wrote 2 buffers (0.0%); 0 WAL file(s)
added, 0 removed, 0 recycled; write=0.004 s, sync=0.004 s, total=0.025
s; sync files=2, longest=0.003 s, average=0.002 s; distance=10 kB,
estimate=10 kB

Regards,
Bharath Rupireddy.