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.
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.
1. No need to set btype in processUnblockedClients(), since clients
flagged REDIS_UNBLOCKED should have it already cleared.
2. When putting clients in the unblocked clients list, clientsArePaused()
should flag them with REDIS_UNBLOCKED. Not strictly needed with the
current code but is more coherent.
1. No need to set btype in processUnblockedClients(), since clients
flagged REDIS_UNBLOCKED should have it already cleared.
2. When putting clients in the unblocked clients list, clientsArePaused()
should flag them with REDIS_UNBLOCKED. Not strictly needed with the
current code but is more coherent.
When the list of unblocked clients were processed, btype was set to
blocking type none, but the client remained flagged with REDIS_BLOCKED.
When timeout is reached (or when the client disconnects), unblocking it
will trigger an assertion.
There is no need to process pending requests from blocked clients, so
now clientsArePaused() just avoid touching blocked clients.
Close#2467.
When the list of unblocked clients were processed, btype was set to
blocking type none, but the client remained flagged with REDIS_BLOCKED.
When timeout is reached (or when the client disconnects), unblocking it
will trigger an assertion.
There is no need to process pending requests from blocked clients, so
now clientsArePaused() just avoid touching blocked clients.
Close#2467.
This commit moves the process of generating a new config epoch without
consensus out of the clusterCommand() implementation, in order to make
it reusable for other reasons (current target is to have a CLUSTER
FAILOVER option forcing the failover when no master majority is
reachable).
Moreover the commit moves other functions which are similarly related to
config epochs in a new logical section of the cluster.c file, just for
clarity.
This commit moves the process of generating a new config epoch without
consensus out of the clusterCommand() implementation, in order to make
it reusable for other reasons (current target is to have a CLUSTER
FAILOVER option forcing the failover when no master majority is
reachable).
Moreover the commit moves other functions which are similarly related to
config epochs in a new logical section of the cluster.c file, just for
clarity.
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.
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.
