Re: [tarantool-patches] [PATCH v4 2/2] box: adds replication sync after cfg. update

[Olga Krishtal <krishtal.olja@gmail.com>]

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Thanks for the review!

вт, 28 авг. 2018 г. в 18:58, Vladimir Davydov <vdavydov.dev@gmail.com>:

> On Tue, Aug 28, 2018 at 02:43:28PM +0300, Olga Arkhangelskaia wrote:
> > When replica reconnects to replica set not for the first time, we
> > suffer from absence of synchronization. Such behavior leads to giving
> > away outdated data.
> >
> > Closes #3427
>
> Please write a documentation request.
>

Ok


>
> > diff --git a/src/box/box.cc b/src/box/box.cc
> > index be5077da8..aaae4219f 100644
> > --- a/src/box/box.cc
> > +++ b/src/box/box.cc
> > @@ -634,6 +634,11 @@ box_set_replication(void)
> >       box_sync_replication(true);
> >       /* Follow replica */
> >       replicaset_follow();
> > +     /* Sync replica up to quorum */
> > +     if (!replicaset_sync()) {
> > +             tnt_raise(ClientError, ER_CFG, "replication",
> > +                       "failed to connect to one or more replicas");
> > +     }
>
> Throwing ER_CFG error from box.cfg() and still applying the new
> replication configuration looks weird. We should either revert the
> configuration back to what we had before box.cfg() was called or not
> throw exceptions.
>
> Reverting configuration seems to be unreasonable, because we could've
> applied some rows from the new replicas.
>
> We discussed the matter with Georgy and Kostja and agreed that instead
> an instance should enter the orphan mode, just like it does on initial
> configuration.
>
>

Just curious, why?  How can we applied changes if box.cfg throws an error?
Or I miss smth?
Ok



> Sorry, we didn't come to an agreement earlier.
>
> Please rework and add a test case.
>
> > diff --git a/test/replication/sync.test.lua
> b/test/replication/sync.test.lua
> > new file mode 100644
> > index 000000000..4c2b55af8
> > --- /dev/null
> > +++ b/test/replication/sync.test.lua
> > @@ -0,0 +1,38 @@
> > +--
> > +-- gh-3427: no sync after configuration update
> > +--
> > +
> > +env = require('test_run')
> > +test_run = env.new()
> > +engine = test_run:get_cfg('engine')
> > +
> > +box.schema.user.grant('guest', 'replication')
> > +
> > +test_run:cmd("create server replica with rpl_master=default,
> script='replication/replica.lua'")
> > +test_run:cmd("start server replica")
> > +
> > +s = box.schema.space.create('test', {engine = engine})
> > +index = s:create_index('primary')
> > +
> > +-- change replica configuration
> > +test_run:cmd("switch replica")
> > +box.cfg{replication_sync_lag = 0.1}
> > +replication = box.cfg.replication
> > +box.cfg{replication={}}
> > +
> > +test_run:cmd("switch default")
> > +-- insert values on the master while replica is unconfigured
> > +a = 3000 box.begin() while a > 0 do a = a-1 box.space.test:insert{a,a}
> end box.commit()
>
> Nit: for i = 1, 100 do ... end


> Anyway, why 3000? When I change it to 1000 or even 100 the test still
> passes with this patch and fails without it.
>
>
I used 3000 because when there is no patch and I put replica into sleep for
replication sync lag (0.1) arrives nearly 2500 tuples.



> Also, I'd like to see a test case that checks that in case
> box.cfg.replication_sync_lag is big, not all records arrive
> by the time box.cfg{replication} returns.
>
>
You mean see difference in tuples count in case when replicas are synced,
however due to lag, but not due to data has arrived?


> And a test case that checks that tarantool enters the orphan mode
> if it fails to sync.
>
> Please add.
>


Ok


>
> > +
> > +test_run:cmd("switch replica")
> > +box.cfg{replication = replication}
> > +
> > +box.space.test:count() == 3000
>
> Nit: better do
>
> box.space.test:count() -- 3000
>
> The reject file will be more informative in case of error then.
>

So I need 3 test case
Test that we are synced.
Test with sync and big lag.
Test with failed sync - orphan mode?



>
> > +
> > +test_run:cmd("switch default")
> > +
> > +-- cleanup
> > +test_run:cmd("stop server replica")
> > +test_run:cmd("cleanup server replica")
> > +box.space.test:drop()
> > +box.schema.user.revoke('guest', 'replication')
>

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