[tarantool-patches] Re: [PATCH 05/10] vinyl: don't purge deleted runs from vylog on compaction

[Konstantin Osipov <kostja@tarantool.org>]

* Vladimir Davydov <vdavydov.dev@gmail.com> [19/05/17 17:54]:
> After compacting runs, we first mark them as dropped (VY_LOG_DROP_RUN),
> then try to delete their files unless they are needed for recovery from
> the checkpoint, and finally mark them as not needed in the vylog
> (VY_LOG_FORGET_RUN). There's a potential race sitting here: the problem
> is the garbage collector might kick in after files are dropped, but
> before they are marked as not needed. If this happens, there will be
> runs that have two VY_LOG_FORGET_RUN records, which will break recovery:
> 
>   Run XX is forgotten, but not registered
> 
> The following patches make the race more likely to happen so let's
> eliminate it by making the garbage collector the only one who can mark
> runs as not needed (i.e. write VY_LOG_FORGET_RUN record). There will
> be no warnings, because the garbage collector silently ignores ENOENT
> errors, see vy_gc().
> 
> Another good thing about this patch is that now we never yield inside
> a vylog transaction, which makes it easier to remove the vylog latch
> blocking implementation of transactional DDL.
> ---

This is also a good one, LGTM.


-- 
Konstantin Osipov, Moscow, Russia