Re: [Tarantool-patches] [PATCH] vinyl: bump dump_generation in case scheduler doesn't catch up with DDL

[Nikita Pettik <korablev@tarantool.org>]

On 10 Jun 18:31, Aleksandr Lyapunov wrote:
> Thanks for the patch, lgtm.
> Actually it's a bit complicated, as well vy_scheduler itself.

Pushed to master, 2.4, 2.3 and 1.10. Changelogs are updated
correspondingly. Branch is dropped.
 
> > It may turn out that dump_generation does not catch up with current
> > generation and no other dump tasks are in progress. This may happen
> > dump process is throttled due to errors. In this case generation is
> > bumped but dump_generation is not (since dump is not completed). In
> > turn, throttling opens a window for DDL operations. For instance, index
> > dropping and creation of new one results in mentioned situation:
> > 
> > box.snapshot() -- fails for some reason; next attempt at dumping will be
> >                 -- taken in one second.
> > s:drop() -- drop index to be dumped
> > s = box.schema.space.create('test', {engine = 'vinyl'})
> > -- create new one (its mem generation is greater than scheduler's one)
> > i = s:create_index('pk')
> > 
> > Closes #4821
> > ---
> > Note that current fix is only workaround amd doesn't pretend to be
> > the most proper one. Alternatively, we can rollback scheduler
> > generation in case dump is failed and index to be dumped is dropped.
> > 
> > Branch:https://github.com/tarantool/tarantool/tree/np/gh-4821-scheduler-gen-assert
> > Issue:https://github.com/tarantool/tarantool/issues/4821
> > 
> >   src/box/vy_scheduler.c                        | 14 ++++-
> >   .../gh-4821-ddl-during-throttled-dump.result  | 57 +++++++++++++++++++
> >   ...gh-4821-ddl-during-throttled-dump.test.lua | 22 +++++++
> >   test/vinyl/suite.ini                          |  2 +-
> >   4 files changed, 92 insertions(+), 3 deletions(-)
> >   create mode 100644 test/vinyl/gh-4821-ddl-during-throttled-dump.result
> >   create mode 100644 test/vinyl/gh-4821-ddl-during-throttled-dump.test.lua
> > 
> > diff --git a/src/box/vy_scheduler.c b/src/box/vy_scheduler.c
> > index bf4c3fe58..880304b66 100644
> > --- a/src/box/vy_scheduler.c
> > +++ b/src/box/vy_scheduler.c
> > @@ -1846,9 +1846,19 @@ retry:
> >   	/*
> >   	 * Dump is in progress, but all eligible LSM trees are
> >   	 * already being dumped. Wait until the current round
> > -	 * is complete.
> > +	 * is complete. But if there's no any other tasks
> > +	 * in progress, it may mean that dump_generation does
> > +	 * not catch up with current generation. This may happen
> > +	 * due to failed dump process (i.e. generation is bumped
> > +	 * but dump_generation is not). In turn, after dump is failed,
> > +	 * next dump will be throttled which opens a window for DDL
> > +	 * operations. For instance, index dropping and creation of
> > +	 * new one results in mentioned situation.
> >   	 */
> > -	assert(scheduler->dump_task_count > 0);
> > +	if (scheduler->dump_task_count == 0) {
> > +		scheduler->dump_generation = vy_lsm_generation(lsm);
> > +		goto retry;
> > +	}
> >   no_task:
> >   	if (worker != NULL)
> >   		vy_worker_pool_put(worker);
>