Re: Report checkpoint progress with pg_stat_progress_checkpoint (was: Report checkpoint progress in server logs) - Mailing list pgsql-hackers

+/* Kinds of checkpoint (as advertised via PROGRESS_CHECKPOINT_KIND) */
+#define PROGRESS_CHECKPOINT_KIND_WAL                0
+#define PROGRESS_CHECKPOINT_KIND_TIME               1
+#define PROGRESS_CHECKPOINT_KIND_FORCE              2
+#define PROGRESS_CHECKPOINT_KIND_UNKNOWN            3

On what basis have you classified the above into the various types of
checkpoints? AFAIK, the first two types are based on what triggered
the checkpoint (whether it was the checkpoint_timeout or maz_wal_size
settings) while the third type indicates the force checkpoint that can
happen when the checkpoint is triggered for various reasons e.g. .
during createb or dropdb etc. This is quite possible that both the
PROGRESS_CHECKPOINT_KIND_TIME and PROGRESS_CHECKPOINT_KIND_FORCE flags
are set for the checkpoint because multiple checkpoint requests are
processed at one go, so what type of checkpoint would that be?

+        */
+       if ((flags & (CHECKPOINT_IS_SHUTDOWN |
CHECKPOINT_END_OF_RECOVERY)) == 0)
+       {
+
pgstat_progress_start_command(PROGRESS_COMMAND_CHECKPOINT,
InvalidOid);
+               checkpoint_progress_update_param(flags,
PROGRESS_CHECKPOINT_PHASE,
+
          PROGRESS_CHECKPOINT_PHASE_INIT);
+               if (flags & CHECKPOINT_CAUSE_XLOG)
+                       checkpoint_progress_update_param(flags,
PROGRESS_CHECKPOINT_KIND,
+
                  PROGRESS_CHECKPOINT_KIND_WAL);
+               else if (flags & CHECKPOINT_CAUSE_TIME)
+                       checkpoint_progress_update_param(flags,
PROGRESS_CHECKPOINT_KIND,
+
                  PROGRESS_CHECKPOINT_KIND_TIME);
+               else if (flags & CHECKPOINT_FORCE)
+                       checkpoint_progress_update_param(flags,
PROGRESS_CHECKPOINT_KIND,
+
                  PROGRESS_CHECKPOINT_KIND_FORCE);
+               else
+                       checkpoint_progress_update_param(flags,
PROGRESS_CHECKPOINT_KIND,
+
                  PROGRESS_CHECKPOINT_KIND_UNKNOWN);
+       }
+}

--
With Regards,
Ashutosh Sharma.

On Thu, Feb 10, 2022 at 12:23 PM Nitin Jadhav
<nitinjadhavpostgres@gmail.com> wrote:
>
> > > We need at least a trace of the number of buffers to sync (num_to_scan) before the checkpoint start, instead of
justemitting the stats at the end.
 
> > >
> > > Bharat, it would be good to show the buffers synced counter and the total buffers to sync, checkpointer pid,
substepit is running, whether it is on target for completion, checkpoint_Reason
 
> > > (manual/times/forced). BufferSync has several variables tracking the sync progress locally, and we may need some
refactoringhere.
 
> >
> > I agree to provide above mentioned information as part of showing the
> > progress of current checkpoint operation. I am currently looking into
> > the code to know if any other information can be added.
>
> Here is the initial patch to show the progress of checkpoint through
> pg_stat_progress_checkpoint view. Please find the attachment.
>
> The information added to this view are pid - process ID of a
> CHECKPOINTER process, kind - kind of checkpoint indicates the reason
> for checkpoint (values can be wal, time or force), phase - indicates
> the current phase of checkpoint operation, total_buffer_writes - total
> number of buffers to be written, buffers_processed - number of buffers
> processed, buffers_written - number of buffers written,
> total_file_syncs - total number of files to be synced, files_synced -
> number of files synced.
>
> There are many operations happen as part of checkpoint. For each of
> the operation I am updating the phase field of
> pg_stat_progress_checkpoint view. The values supported for this field
> are initializing, checkpointing replication slots, checkpointing
> snapshots, checkpointing logical rewrite mappings, checkpointing CLOG
> pages, checkpointing CommitTs pages, checkpointing SUBTRANS pages,
> checkpointing MULTIXACT pages, checkpointing SLRU pages, checkpointing
> buffers, performing sync requests, performing two phase checkpoint,
> recycling old XLOG files and Finalizing. In case of checkpointing
> buffers phase, the fields total_buffer_writes, buffers_processed and
> buffers_written shows the detailed progress of writing buffers. In
> case of performing sync requests phase, the fields total_file_syncs
> and files_synced shows the detailed progress of syncing files. In
> other phases, only the phase field is getting updated and it is
> difficult to show the progress because we do not get the total number
> of files count without traversing the directory. It is not worth to
> calculate that as it affects the performance of the checkpoint. I also
> gave a thought to just mention the number of files processed, but this
> wont give a meaningful progress information (It can be treated as
> statistics). Hence just updating the phase field in those scenarios.
>
> Apart from above fields, I am planning to add few more fields to the
> view in the next patch. That is, process ID of the backend process
> which triggered a CHECKPOINT command, checkpoint start location, filed
> to indicate whether it is a checkpoint or restartpoint and elapsed
> time of the checkpoint operation. Please share your thoughts. I would
> be happy to add any other information that contributes to showing the
> progress of checkpoint.
>
> As per the discussion in this thread, there should be some mechanism
> to show the progress of checkpoint during shutdown and end-of-recovery
> cases as we cannot access pg_stat_progress_checkpoint in those cases.
> I am working on this to use log_startup_progress_interval mechanism to
> log the progress in the server logs.
>
> Kindly review the patch and share your thoughts.
>
>
> On Fri, Jan 28, 2022 at 12:24 PM Bharath Rupireddy
> <bharath.rupireddyforpostgres@gmail.com> wrote:
> >
> > On Fri, Jan 21, 2022 at 11:07 AM Nitin Jadhav
> > <nitinjadhavpostgres@gmail.com> wrote:
> > >
> > > > I think the right choice to solve the *general* problem is the
> > > > mentioned pg_stat_progress_checkpoints.
> > > >
> > > > We may want to *additionally* have the ability to log the progress
> > > > specifically for the special cases when we're not able to use that
> > > > view. And in those case, we can perhaps just use the existing
> > > > log_startup_progress_interval parameter for this as well -- at least
> > > > for the startup checkpoint.
> > >
> > > +1
> > >
> > > > We need at least a trace of the number of buffers to sync (num_to_scan) before the checkpoint start, instead of
justemitting the stats at the end.
 
> > > >
> > > > Bharat, it would be good to show the buffers synced counter and the total buffers to sync, checkpointer pid,
substepit is running, whether it is on target for completion, checkpoint_Reason
 
> > > > (manual/times/forced). BufferSync has several variables tracking the sync progress locally, and we may need
somerefactoring here.
 
> > >
> > > I agree to provide above mentioned information as part of showing the
> > > progress of current checkpoint operation. I am currently looking into
> > > the code to know if any other information can be added.
> >
> > As suggested in the other thread by Julien, I'm changing the subject
> > of this thread to reflect the discussion.
> >
> > Regards,
> > Bharath Rupireddy.