From: Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>,
tml <tarantool-patches@dev.tarantool.org>
Subject: Re: [Tarantool-patches] [PATCH v8 1/2] applier: send transaction's first row WAL time in the applier_writer_f
Date: Thu, 17 Jun 2021 12:16:35 +0300 [thread overview]
Message-ID: <68c348fe-7029-db28-8457-a95d03e6923e@tarantool.org> (raw)
In-Reply-To: <YMn9dg8JNQm5Xl0p@grain>
16.06.2021 16:32, Cyrill Gorcunov пишет:
> On Tue, Jun 15, 2021 at 12:36:02PM +0300, Serge Petrenko wrote:
>>> @@ -193,6 +196,16 @@ applier_writer_f(va_list ap)
>>> applier->has_acks_to_send = false;
>>> struct xrow_header xrow;
>>> xrow_encode_vclock(&xrow, &replicaset.vclock);
>>> + /*
>>> + * For relay lag statistics we report last
>>> + * written transaction timestamp in tm field.
>>> + *
>>> + * Replica might be dead already so we have to
>>> + * test on each iteration.
>>> + */
>>> + struct replica *r = replica_by_id(replica_id);
>>> + if (likely(r != NULL))
>>> + xrow.tm = r->applier_txn_start_tm;
>> How could a replica be dead here?
>> AFAIR we delete a replica only when it's deleted from _cluster. Shouldn't
>> the applier writer be dead as well by that time?
> Before accessing replica_by_id we're sitting in event loop trying to
> fetch data from the network. Which means an admin may cleanup the
> entry manually before we get back to this code in result we will
> get a nil dereference (if only I'm not missing something).
I mean that this code you're referring to is executed in a
while (!fiber_is_cancelled()) {...} loop.
IIRC applier->writer gets cancelled as soon as replica is unregistered.
So even if someone deletes the entry manually the writer will exit the loop
before getting a nil dereference.
P.S. I couldn't find this anywhere in code so let's leave the check.
--
Serge Petrenko
next prev parent reply other threads:[~2021-06-17 9:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-07 15:55 [Tarantool-patches] [PATCH v8 0/2] relay: provide downstream lag information Cyrill Gorcunov via Tarantool-patches
2021-06-07 15:55 ` [Tarantool-patches] [PATCH v8 1/2] applier: send transaction's first row WAL time in the applier_writer_f Cyrill Gorcunov via Tarantool-patches
2021-06-07 19:20 ` Vladislav Shpilevoy via Tarantool-patches
2021-06-15 9:36 ` Serge Petrenko via Tarantool-patches
2021-06-16 13:32 ` Cyrill Gorcunov via Tarantool-patches
2021-06-17 9:16 ` Serge Petrenko via Tarantool-patches [this message]
2021-06-07 15:55 ` [Tarantool-patches] [PATCH v8 2/2] relay: provide information about downstream lag Cyrill Gorcunov via Tarantool-patches
2021-06-07 19:21 ` Vladislav Shpilevoy via Tarantool-patches
2021-06-08 8:40 ` Cyrill Gorcunov via Tarantool-patches
2021-06-08 9:58 ` Cyrill Gorcunov via Tarantool-patches
2021-06-08 18:15 ` Vladislav Shpilevoy via Tarantool-patches
2021-06-15 10:03 ` Serge Petrenko via Tarantool-patches
2021-06-17 6:55 ` Cyrill Gorcunov via Tarantool-patches
2021-06-17 9:01 ` Serge Petrenko via Tarantool-patches
2021-06-17 9:58 ` Cyrill Gorcunov via Tarantool-patches
2021-06-07 19:20 ` [Tarantool-patches] [PATCH v8 0/2] relay: provide downstream lag information Vladislav Shpilevoy via Tarantool-patches
2021-06-07 20:00 ` Cyrill Gorcunov via Tarantool-patches
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