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Redis Cluster: delay state change when in the majority again.

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As specified in the Redis Cluster specification, when a node can reach
the majority again after a period in which it was partitioend away with
the minorty of masters, wait some time before accepting queries, to
provide a reasonable amount of time for other nodes to upgrade its
configuration.

This lowers the probabilities of both a client and a master with not
updated configuration to rejoin the cluster at the same time, with a
stale master accepting writes.
This commit is contained in:
antirez 2013-12-20 09:56:18 +01:00
parent 305d7f29f3
commit a2c938c834
1 changed files with 33 additions and 14 deletions
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47
src/cluster.c
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@ -2205,20 +2205,24 @@ int clusterDelNodeSlots(clusterNode *node) {
/* -----------------------------------------------------------------------------
* Cluster state evaluation function
* -------------------------------------------------------------------------- */
#define REDIS_CLUSTER_MAX_REJOIN_DELAY 5000
void clusterUpdateState(void) {
int j, initial_state = server.cluster->state;
int j, new_state;
int unreachable_masters = 0;
static mstime_t among_minority_time;
/* Start assuming the state is OK. We'll turn it into FAIL if there
* are the right conditions. */
server.cluster->state = REDIS_CLUSTER_OK;
new_state = REDIS_CLUSTER_OK;
/* Check if all the slots are covered. */
for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
if (server.cluster->slots[j] == NULL ||
server.cluster->slots[j]->flags & (REDIS_NODE_FAIL))
{
server.cluster->state = REDIS_CLUSTER_FAIL;
new_state = REDIS_CLUSTER_FAIL;
break;
}
}
@ -2248,24 +2252,39 @@ void clusterUpdateState(void) {
/* If we can't reach at least half the masters, change the cluster state
* to FAIL, as we are not even able to mark nodes as FAIL in this side
* of the netsplit because of lack of majority.
*
* TODO: when this condition is entered, we should not undo it for some
* (small) time after the majority is reachable again, to make sure that
* other nodes have enough time to inform this node of a configuration change.
* Otherwise a client with an old routing table may write to this node
* and later it may turn into a slave losing the write. */
* of the netsplit because of lack of majority. */
{
int needed_quorum = (server.cluster->size / 2) + 1;
if (unreachable_masters >= needed_quorum)
server.cluster->state = REDIS_CLUSTER_FAIL;
if (unreachable_masters >= needed_quorum) {
new_state = REDIS_CLUSTER_FAIL;
among_minority_time = mstime();
}
}
/* Log a state change */
if (initial_state != server.cluster->state)
if (new_state != server.cluster->state) {
mstime_t rejoin_delay = server.cluster_node_timeout;
/* If the instance is a master and was partitioned away with the
* minority, don't let it accept queries for some time after the
* partition heals, to make sure there is enough time to receive
* a configuration update. */
if (rejoin_delay > REDIS_CLUSTER_MAX_REJOIN_DELAY)
rejoin_delay = REDIS_CLUSTER_MAX_REJOIN_DELAY;
if (new_state == REDIS_CLUSTER_OK &&
server.cluster->myself->flags & REDIS_NODE_MASTER &&
mstime() - among_minority_time < rejoin_delay)
{
return;
}
/* Change the state and log the event. */
redisLog(REDIS_WARNING,"Cluster state changed: %s",
server.cluster->state == REDIS_CLUSTER_OK ? "ok" : "fail");
new_state == REDIS_CLUSTER_OK ? "ok" : "fail");
server.cluster->state = new_state;
}
}
/* This function is called after the node startup in order to verify that data