Ben Pfaff <b...@ovn.org> wrote on 08/20/2016 10:32:50 AM:
> From: Ben Pfaff <b...@ovn.org>
> To: Ryan Moats/Omaha/IBM@IBMUS
> Cc: ovs dev <dev@openvswitch.org>
> Date: 08/20/2016 10:33 AM
> Subject: another possible cause of incremental update problems
>
> There are additional possible causes of incremental update problems that
> I haven't previously seen mentioned here. If you look at the functions
> that implement incremental update, they tend to start with:
>
> if (!ctx->ovnsb_idl_txn) {
> return NULL;
> }
>
> or similar. This makes sense, because there is no point in composing an
> update if it can't be committed. However, because the main loop call
> ovsdb_idl_txn_clear() on every iteration, that means that any updates
> from this iteration will be lost.
>
> Also, transactions can fail. In that case, the transaction needs to be
> recomposed and retried. ovn-controller currently doesn't have any
> mechanism for that.
Yep, there are all sorts of interesting failure modes, but the key point
I was looking to make with the analysis was that *even if everything
worked perfectly* the code doesn't buy us what I hoped it would buy when
I started - it ended up in a different place where the tradeoff no
longer makes sense to me... (c'est la vie)
As a side note, I have the revert change done and I'll be sending that
out shortly. The quiet mode change isn't passing all of the current unit
test cases (yet), so I'm still looking at it. I plan on sending it out
on Monday, either as a real change if I figure out what's going wrong
in the unit tests or as an RFC if I don't...
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