Thread: Add CHECKPOINT_REQUESTED flag to the log message in LogCheckpointStart()

Hi,

I have noticed that the CHECKPOINT_REQUESTED flag information is not
present in the log message of LogCheckpointStart() function. I would
like to understand if it was missed or left intentionally. The log
message describes all the possible checkpoint flags except
CHECKPOINT_REQUESTED flag. I feel we should support this. Thoughts?

Please find the patch attached.

Thanks & Regards,
Nitin Jadhav

On Wed, Mar 2, 2022 at 5:41 PM Nitin Jadhav
<nitinjadhavpostgres@gmail.com> wrote:
>
> Hi,
>
> I have noticed that the CHECKPOINT_REQUESTED flag information is not
> present in the log message of LogCheckpointStart() function. I would
> like to understand if it was missed or left intentionally. The log
> message describes all the possible checkpoint flags except
> CHECKPOINT_REQUESTED flag. I feel we should support this. Thoughts?

I don't think that's useful. Being in LogCheckpointStart
(CreateCheckPoint or CreateRestartPoint) itself means that somebody
has requested a checkpoint. Having CHECKPOINT_REQUESTED doesn't add
any value.

I would suggest removing the CHECKPOINT_REQUESTED flag as it's not
being used anywhere instead CheckpointerShmem->ckpt_flags is used as
an indication of the checkpoint requested in CheckpointerMain [1]. If
others don't agree to remove as it doesn't cause any harm, then, I
would  add something like this for more readability:

         if ((((volatile CheckpointerShmemStruct *)
CheckpointerShmem)->ckpt_flags) & CHECKPOINT_REQUESTED))
        {
            do_checkpoint = true;
            PendingCheckpointerStats.m_requested_checkpoints++;
        }

[1]
        /*
         * Detect a pending checkpoint request by checking whether the flags
         * word in shared memory is nonzero.  We shouldn't need to acquire the
         * ckpt_lck for this.
         */
        if (((volatile CheckpointerShmemStruct *)
CheckpointerShmem)->ckpt_flags)
        {
            do_checkpoint = true;
            PendingCheckpointerStats.m_requested_checkpoints++;
        }

Regards,
Bharath Rupireddy.

At Wed, 2 Mar 2022 18:18:10 +0530, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> wrote in 
> On Wed, Mar 2, 2022 at 5:41 PM Nitin Jadhav
> <nitinjadhavpostgres@gmail.com> wrote:
> >
> > Hi,
> >
> > I have noticed that the CHECKPOINT_REQUESTED flag information is not
> > present in the log message of LogCheckpointStart() function. I would
> > like to understand if it was missed or left intentionally. The log
> > message describes all the possible checkpoint flags except
> > CHECKPOINT_REQUESTED flag. I feel we should support this. Thoughts?
> 
> I don't think that's useful. Being in LogCheckpointStart
> (CreateCheckPoint or CreateRestartPoint) itself means that somebody
> has requested a checkpoint. Having CHECKPOINT_REQUESTED doesn't add
> any value.

Agreed.

> I would suggest removing the CHECKPOINT_REQUESTED flag as it's not
> being used anywhere instead CheckpointerShmem->ckpt_flags is used as
> an indication of the checkpoint requested in CheckpointerMain [1]. If

Actually no one does but RequestCheckpoint() accepts 0 as flags.
Checkpointer would be a bit more complex without CHECKPOINT_REQUESTED.
I don't think it does us any good to get rid of the flag value.

> others don't agree to remove as it doesn't cause any harm, then, I
> would  add something like this for more readability:

     if (((volatile CheckpointerShmemStruct *)
-          CheckpointerShmem)->ckpt_flags)
+          CheckpointerShmem)->ckpt_flags) & CHECKPOINT_REQUESTED))

I don't particularly object to this, but I don't think that change
makes the code significantly easier to read either.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

On Thu, Mar 03, 2022 at 09:39:37AM +0900, Kyotaro Horiguchi wrote:
> At Wed, 2 Mar 2022 18:18:10 +0530, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> wrote in
>> I don't think that's useful. Being in LogCheckpointStart
>> (CreateCheckPoint or CreateRestartPoint) itself means that somebody
>> has requested a checkpoint. Having CHECKPOINT_REQUESTED doesn't add
>> any value.
>
> Agreed.

Exactly my impression.  This would apply now to the WAL shutdown code
paths, and I'd suspect that the callers of CreateCheckPoint() are not
going to increase soon.  The point is: the logs already provide some
contexts for any of those callers so I see no need for this additional
information.

> Actually no one does but RequestCheckpoint() accepts 0 as flags.
> Checkpointer would be a bit more complex without CHECKPOINT_REQUESTED.
> I don't think it does us any good to get rid of the flag value.

I'd rather keep this code as-is.
--
Michael

At Thu, 3 Mar 2022 10:27:10 +0900, Michael Paquier <michael@paquier.xyz> wrote in 
> On Thu, Mar 03, 2022 at 09:39:37AM +0900, Kyotaro Horiguchi wrote:
> > At Wed, 2 Mar 2022 18:18:10 +0530, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> wrote in 
> >> I don't think that's useful. Being in LogCheckpointStart
> >> (CreateCheckPoint or CreateRestartPoint) itself means that somebody
> >> has requested a checkpoint. Having CHECKPOINT_REQUESTED doesn't add
> >> any value.
> > 
> > Agreed.
> 
> Exactly my impression.  This would apply now to the WAL shutdown code
> paths, and I'd suspect that the callers of CreateCheckPoint() are not
> going to increase soon.  The point is: the logs already provide some
> contexts for any of those callers so I see no need for this additional
> information.
> 
> > Actually no one does but RequestCheckpoint() accepts 0 as flags.
> > Checkpointer would be a bit more complex without CHECKPOINT_REQUESTED.
> > I don't think it does us any good to get rid of the flag value.
> 
> I'd rather keep this code as-is.

I fail to identify the nuance of the phrase, so just for a
clarification.  In short, I think we should keep the exiting code
as-is.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center