Re: logical replication empty transactions

On Mon, Aug 16, 2021 at 4:44 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:

> I have reviewed the v13-0001 patch.
>
> Apply / build / test was all OK
>
> Below are my code review comments.
>
> //////////
>
> Comments for v13-0001
> =====================
>
> 1. Patch comment
>
> =>
>
> Probably this comment should include some description for the new
> "keepalive" logic as well.

Added.

>
> ------
>
> 2. src/backend/replication/syncrep.c - new function
>
> @@ -330,6 +330,18 @@ SyncRepWaitForLSN(XLogRecPtr lsn, bool commit)
> }
>
> /*
> + * Check if Sync Rep is enabled
> + */
> +bool
> +SyncRepEnabled(void)
> +{
> + if (SyncRepRequested() && ((volatile WalSndCtlData *)
> WalSndCtl)->sync_standbys_defined)
> + return true;
> + else
> + return false;
> +}
> +
>
> 2a. Function comment =>
>
> Why abbreviations in the comment? Why not say "synchronous
> replication" instead of "Sync Rep".
>

Changed.

> ~~
>
> 2b. if/else =>
>
> Remove the if/else. e.g.
>
> return SyncRepRequested() && ((volatile WalSndCtlData *)
> WalSndCtl)->sync_standbys_defined;
>
> ~~

Changed.

>
> 2c. Call the new function =>
>
> There is some existing similar code in SyncRepWaitForLSN(), e.g.
>
> if (!SyncRepRequested() ||
> !((volatile WalSndCtlData *) WalSndCtl)->sync_standbys_defined)
> return;
>
> Now that you have a new function you maybe can call it from here, e.g.
>
> if (!SyncRepEnabled())
> return;
>

Updated.

> ------
>
> 3. src/backend/replication/walsender.c - whitespace
>
> + if (send_keep_alive)
> + force_keep_alive_syncrep = true;
> +
> +
>
> =>
>
> Extra blank line?

Removed.

>
> ------
>
> 4. src/backend/replication/walsender.c - call keepalive
>
> if (MyWalSnd->flush < sentPtr &&
> MyWalSnd->write < sentPtr &&
> !waiting_for_ping_response)
> + {
> WalSndKeepalive(false);
> + }
> + else
> + {
> + if (force_keep_alive_syncrep && SyncRepEnabled())
> + WalSndKeepalive(false);
> + }
>
>
> 4a. Move the SynRepEnabled() call =>
>
> I think it is not necessary to call the SynRepEnabled() here. Instead,
> it might be better if this is called back when you assign the
> force_keep_alive_syncrep flag. So change the WalSndUpdateProgress,
> e.g.
>
> BEFORE
> if (send_keep_alive)
> force_keep_alive_syncrep = true;
> AFTER
> force_keep_alive_syncrep = send_keep_alive && SyncRepEnabled();
>
> Note: Also, that assignment also deserves a big comment to say what it is doing.
>
> ~~

changed.

>
> 4b. Change the if/else =>
>
> If you make the change for 4a. then perhaps the keepalive if/else is
> overkill and could be changed.e.g.
>
> if (force_keep_alive_syncrep ||
> MyWalSnd->flush < sentPtr &&
> MyWalSnd->write < sentPtr &&
> !waiting_for_ping_response)
> WalSndKeepalive(false);
>

Changed.

regards,
Ajin Cherian
Fujitsu Australia