From: | shveta malik <shveta(dot)malik(at)gmail(dot)com> |
---|---|
To: | Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
Cc: | "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, shveta malik <shveta(dot)malik(at)gmail(dot)com> |
Subject: | Re: promotion related handling in pg_sync_replication_slots() |
Date: | 2024-04-19 06:07:07 |
Message-ID: | CAJpy0uA68sK6wPNedbuN-2_ZXfcHfL1U9aUKHHtfPNcb5SqZHQ@mail.gmail.com |
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On Fri, Apr 19, 2024 at 10:53 AM Bertrand Drouvot
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> Hi,
>
> On Thu, Apr 18, 2024 at 05:36:05PM +0530, shveta malik wrote:
> > Please find v8 attached. Changes are:
>
> Thanks!
>
> A few comments:
Thanks for reviewing.
> 1 ===
>
> @@ -1440,7 +1461,7 @@ ReplSlotSyncWorkerMain(char *startup_data, size_t startup_data_len)
> * slotsync_worker_onexit() but that will need the connection to be made
> * global and we want to avoid introducing global for this purpose.
> */
> - before_shmem_exit(slotsync_failure_callback, PointerGetDatum(wrconn));
> + before_shmem_exit(slotsync_worker_disconnect, PointerGetDatum(wrconn));
>
> The comment above this change still states "Register the failure callback once
> we have the connection", I think it has to be reworded a bit now that v8 is
> making use of slotsync_worker_disconnect().
>
> 2 ===
>
> + * Register slotsync_worker_onexit() before we register
> + * ReplicationSlotShmemExit() in BaseInit(), to ensure that during exit of
> + * slot sync worker, ReplicationSlotShmemExit() is called first, followed
> + * by slotsync_worker_onexit(). Startup process during promotion waits for
>
> Worth to mention in shmem_exit() (where it "while (--before_shmem_exit_index >= 0)"
> or before the shmem_exit() definition) that ReplSlotSyncWorkerMain() relies on
> this LIFO behavior? (not sure if there is other "strong" LIFO requirement in
> other part of the code).
I see other modules as well relying on LIFO behavior.
Please see applyparallelworker.c where
'before_shmem_exit(pa_shutdown)' is needed to be done after
'before_shmem_exit(logicalrep_worker_onexit)' (commit id 3d144c6).
Also in postinit.c, I see such comments atop
'before_shmem_exit(ShutdownPostgres, 0)'.
I feel we can skip adding this specific comment about
ReplSlotSyncWorkerMain() in ipc.c, as none of the other modules has
also not added any. I will address the rest of your comments in the
next version.
> 3 ===
>
> + * Startup process during promotion waits for slot sync to finish and it
> + * does that by checking the 'syncing' flag.
>
> worth to mention ShutDownSlotSync()?
>
> 4 ===
>
> I did a few tests manually (launching ShutDownSlotSync() through gdb / with and
> without sync worker and with / without pg_sync_replication_slots() running
> concurrently) and it looks like it works as designed.
Thanks for testing it.
> Having said that, the logic that is in place to take care of the corner cases
> described up-thread seems reasonable to me.
thanks
Shveta
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