[tarantool-patches] [PATCH v2 5/5] Disallow lsn gaps while vclock following
Vladimir Davydov
vdavydov.dev at gmail.com
Mon Jan 28 15:18:59 MSK 2019
On Tue, Jan 22, 2019 at 01:31:13PM +0300, Georgy Kirichenko wrote:
> Only one-step vclock following is allowed. This enforces wal and
> replication consistency against out of order execution.
Again, quite an obscure commit message. Please try to explain why you do
what you do so that even a sync replication noob like me can understand
it.
>
> Prerequisite #980
> ---
> src/box/replication.cc | 1 +
> src/box/vclock.c | 2 +-
> src/box/xrow.c | 2 +-
> test/unit/vclock.cc | 10 +++++-----
> 4 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/src/box/replication.cc b/src/box/replication.cc
> index 51e08886c..ee92a941b 100644
> --- a/src/box/replication.cc
> +++ b/src/box/replication.cc
> @@ -91,6 +91,7 @@ replication_init(void)
> replicaset.replica_by_id = (struct replica **)calloc(VCLOCK_MAX, sizeof(struct replica *));
> latch_create(&replicaset.applier.order_latch);
> vclock_create(&replicaset.applier.vclock);
> + vclock_clear(&replicaset.applier.vclock);
> }
>
> void
> diff --git a/src/box/vclock.c b/src/box/vclock.c
> index c297d1ff9..807da9109 100644
> --- a/src/box/vclock.c
> +++ b/src/box/vclock.c
> @@ -56,7 +56,7 @@ vclock_follow(struct vclock *vclock, uint32_t replica_id, int64_t lsn)
> assert(lsn >= 0);
> assert(replica_id < VCLOCK_MAX);
> int64_t prev_lsn = vclock->lsn[replica_id];
> - assert(lsn > prev_lsn);
> + assert(lsn == prev_lsn + 1);
AFAIU this may break recovery from a WAL created by an older Tarantool
version that allowed LSN gaps.
> /* Easier add each time than check. */
> vclock->map |= 1 << replica_id;
> vclock->lsn[replica_id] = lsn;
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