We wait a fixed amount of time (5 seconds currently) much greater than
the usual Cluster node to node communication latency, before migrating.
This way when a failover occurs, before detecting the new master as a
target for migration, we give the time to its natural slaves (the slaves
of the failed over master) to announce they switched to the new master,
preventing an useless migration operation.
Some time ago I broken replicas migration (reported in #2924).
The idea was to prevent masters without replicas from getting replicas
because of replica migration, I remember it to create issues with tests,
but there is no clue in the commit message about why it was so
undesirable.
However my patch as a side effect totally ruined the concept of replicas
migration since we want it to work also for instances that, technically,
never had slaves in the past: promoted slaves.
So now instead the ability to be targeted by replicas migration, is a
new flag "migrate-to". It only applies to masters, and is set in the
following two cases:
1. When a master gets a slave, it is set.
2. When a slave turns into a master because of fail over, it is set.
This way replicas migration targets are only masters that used to have
slaves, and slaves of masters (that used to have slaves... obviously)
and are promoted.
The new flag is only internal, and is never exposed in the output nor
persisted in the nodes configuration, since all the information to
handle it are implicit in the cluster configuration we already have.
There was a bug in Redis Cluster caused by clients blocked in a blocking
list pop operation, for keys no longer handled by the instance, or
in a condition where the cluster became down after the client blocked.
A typical situation is:
1) BLPOP <somekey> 0
2) <somekey> hash slot is resharded to another master.
The client will block forever int this case.
A symmentrical non-cluster-specific bug happens when an instance is
turned from master to slave. In that case it is more serious since this
will desynchronize data between slaves and masters. This other bug was
discovered as a side effect of thinking about the bug explained and
fixed in this commit, but will be fixed in a separated commit.
Before we relied on the global cluster state to make sure all the hash
slots are linked to some node, when getNodeByQuery() is called. So
finding the hash slot unbound was checked with an assertion. However
this is fragile. The cluster state is often updated in the
clusterBeforeSleep() function, and not ASAP on state change, so it may
happen to process clients with a cluster state that is 'ok' but yet
certain hash slots set to NULL.
With this commit the condition is also checked in getNodeByQuery() and
reported with a identical error code of -CLUSTERDOWN but slightly
different error message so that we have more debugging clue in the
future.
Root cause of issue #2288.
Also explicitly set version to 0, add a protocol version define, improve
comments in the gossip structure.
Note that the structure layout is the same after the change, we are just
making the padding explicit with an additional not used 16 bits field.
So this commit is still able to talk with the previous versions of
cluster nodes.
bulk_data field size was not removed from the count. It is not possible
to declare it simply as 'char bulk_data[]' since the structure is nested
into another structure.
- Remove trailing newlines from redis.conf
- Fix comment misspelling
- Clarifies zipEncodeLength usage and a C API mention (#1243, #1242)
- Fix cluster typos (inspired by @papanikge #1507)
- Fix rewite -> rewrite in a few places (inspired by #682)
Closes#1243, #1242, #1507
When node-timeout is too small, in the order of a few milliseconds,
there is no way the voting process can terminate during that time, so we
set a lower limit for the failover timeout of two seconds.
The retry time is set to two times the failover timeout time, so it is
at least 4 seconds.
When a slave requests masters vote for a manual failover, the
REQUEST_AUTH message is flagged in a special way in order to force the
masters to give the authorization even if the master is not marked as
failing.
Note that when we compute the initial delay, there are probably still
more up to date information to receive from slaves with new offsets, so
the delay is recomputed when new data is available.
The two fields are used in order to remember the latest known
replication offset and the time we received it from other slave nodes.
This will be used by slaves in order to start the election procedure
with a delay that is proportional to the rank of the slave among the
other slaves for this master, when sorted for replication offset.
Usually this allows the slave with the most updated offset to win the
election and replace the failing master in the cluster.
All the internal state of cluster involving time is now using mstime_t
and mstime() in order to use milliseconds resolution.
Also the clusterCron() function is called with a 10 hz frequency instead
of 1 hz.
The cluster node_timeout must be also configured in milliseconds by the
user in redis.conf.
