[Tarantool-patches] [PATCH] limbo: introduce request processing hooks

[Cyrill Gorcunov]

On Mon, Jul 12, 2021 at 10:04:56AM +0200, Vladislav Shpilevoy wrote:
> > 
> > And if we filter before the WAL write, we need the second vclock, which
> > Cyrill has introduced.
> 
> Why do you need a second vclock? Why can't you just filter by the
> existing vclock and update it after WAL write like now?

Because the phases are no longer atomic. We can pass "filter" stage,
update our terms, but then WAL process failed (it doesn't matter for
what reason, maybe single disk write failure) so we have to revert
former term value back so the client will retry the operation and
resend us the PROMOTE.