[Tarantool-patches] [RFC] gc/xlog: delay xlog cleanup until relays are subscribed

[Cyrill Gorcunov]

On Thu, Mar 18, 2021 at 08:18:12AM +0300, Konstantin Osipov wrote:
> > > 
> > > Should be in 1.10 as well.
> > 
> > Sure, but first I need to be sure if current rfc is acceptable
> > in general and I didn't miss something. I suspect we might
> > need to extend this code and better to not make some design
> > mistakes which gonna be hard to resolve later. I've a test
> > case for this simply didn't posted it yet.
> 
> This is a case where a configuration setting would be suitable. I
> don't think it's necessary to keep these logs forever by default,
> 4-6 hours should be a good default for many setups. Some will set
> the default to, say, 5 minutes, essentially to keep the old
> behaviour, and some can set it to infinity, to get the current
> behaviour of the patch.
> 
> All tarantool setting follow the convention to start from
> subsystem name, so it got to be wal_{something}, e.g.
> wal_keep_logs

Good point, thanks! Kostya, lets clarify some moments:

1) We introduce "wal_keep_logs" option which defines
   a timeout to kick the cleanup fiber.
2) If node is anonymous replica we simply ignore this
   option.
3) If this option is set then we have a few subcases:
   a) The `_cluster` space is not empty thus thus once
      all replicas are subscribed _before_ the timeout
      expired we trigger the cleanup fiber since it is
      safe to process;
   b) If replicas are not connected and timeout is
      expired we kick the cleanup fiber;

Or you mean to always conside "wal_keep_logs" option
and never trigger the cleanup until it get expired?