On Thu, Nov 12, 2020 at 2:28 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
> On Wed, Nov 11, 2020 at 12:35 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> I have rearranged the code in DecodeCommit/Abort/Prepare so
> > that it does only the required things (like in DecodeCommit was still
> > processing subtxns even when it has to just perform FinishPrepared,
> > also the stats were not updated properly which I have fixed.) and
> > added/edited the comments. Apart from 0001 and 0002, I have not
> > changed anything in the remaining patches.
>
> One small comment on the patch:
>
> - DecodeCommit(ctx, buf, &parsed, xid);
> + /*
> + * If we have already decoded this transaction data then
> + * DecodeCommit doesn't need to decode it again. This is
> + * possible iff output plugin supports two-phase commits and
> + * doesn't skip the transaction at prepare time.
> + */
> + if (info == XLOG_XACT_COMMIT_PREPARED && ctx->twophase)
> + {
> + already_decoded = !(ctx->callbacks.filter_prepare_cb &&
> + ReorderBufferPrepareNeedSkip(ctx->reorder, xid, parsed.twophase_gid));
> + }
> +
>
> Just a small nitpick but the way already_decoded is assigned here is a
> bit misleading. It appears that the callbacks determine if the
> transaction is already decoded when in
> reality the callbacks only decide if the transaction should skip two
> phase commits. I think it's better to either move it to the if
> condition or if that is too long then have one more variable
> skip_twophase.
>
> if (info == XLOG_XACT_COMMIT_PREPARED && ctx->twophase &&
> !(ctx->callbacks.filter_prepare_cb &&
> ReorderBufferPrepareNeedSkip(ctx->reorder, xid, parsed.twophase_gid)))
> already_decoded = true;
>
> OR
> bool skip_twophase = false;
> skip_twophase = !(ctx->callbacks.filter_prepare_cb &&
> ReorderBufferPrepareNeedSkip(ctx->reorder, xid, parsed.twophase_gid));
> if (info == XLOG_XACT_COMMIT_PREPARED && ctx->twophase && skip_twophase)
> already_decoded = true;
>
Hmm, introducing an additional boolean variable for this doesn't seem
like a good idea neither the other alternative suggested by you. How
about if we change the comment to make it clear. How about: "If output
plugin supports two-phase commits and doesn't skip the transaction at
prepare time then we don't need to decode the transaction data at
commit prepared time as it would have already been decoded at prepare
time."?
--
With Regards,
Amit Kapila.