Re: [tarantool-patches] [PATCH 2/2] On ctl event trigger

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Tue, Aug 28, 2018 at 07:19:13PM +0300, Georgy Kirichenko wrote:
> Introduce a ctl event trigger fired in cases of a bootstrap/recovery status
> changes, a space create/alter/drop action, an applier state change and
> shutdown. Trigger could be set with box.ctl_event even before the first
> box.cfg invocation to control recovery and bootstrap behavior.
> 
> Event constants accessible via box.ctl_event.const()
> There are events:
>   - RECOVERY
>   - SPACE
>   - SHUTDOWN
>   - APPLIER
> 
> A recovery event might have a status:
>    * RECOVERY_SNAPSHOT_START
>    * RECOVERY_SNAPSHOT_DONE
>    * RECOVERY_HOT_STANDBY_START
>    * RECOVERY_HOT_STANDBY_DONE
>    * RECOVERY_XLOGS_DONE
>    * RECOVERY_BOOTSTRAP_START
>    * RECOVERY_BOOTSTRAP_DONE
>    * RECOVERY_INITIAL_JOIN_START
>    * RECOVERY_INITIAL_JOIN_DONE
>    * RECOVERY_FINAL_JOIN_DONE
> 
> A space event consists of space identifier and action:
>    * SPACE_CREATE
>    * SPACE_ALTER
>    * SPACE_DELETE
> 
> An applier event contains peer uuid and state:
>    * APPLIER_OFF
>    * APPLIER_CONNECT
>    * APPLIER_CONNECTED
>    * APPLIER_AUTH
>    * APPLIER_READY
>    * APPLIER_INITIAL_JOIN
>    * APPLIER_FINAL_JOIN
>    * APPLIER_JOINED
>    * APPLIER_SYNC
>    * APPLIER_FOLLOW
>    * APPLIER_STOPPED
>    * APPLIER_DISCONNECTED
>    * APPLIER_LOADING

I can't review this patch properly, because ctl_event.[hc] are missing,
but I've a few notes about the API.

First, I don't understand why you need two kinds of constants. I mean
SPACE and SPACE_CREATE, or RECOVERY and RECOVERY_SNAPSHOT_START. IMO
there should be just one set of constants.

Second, IMO the event trigger should be installed with box.ctl.on_event
(not box.ctl_event.on_ctl_event), and constants should be defined in
box.ctl.event (not box.ctl_event.const()).

Third, let's start with fewer events, only ones that we need to right
now (e.g. for replication conflict resolution with before_replace).
We can add other events later, when we need to.