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Cluster: function clusterGetSlaveRank() added.

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Return the number of slaves for the same master having a better
replication offset of the current slave, that is, the slave "rank" used
to pick a delay before the request for election.
This commit is contained in:
antirez
2014-01-29 16:39:04 +01:00
parent 40cd38f0c4
commit 6f54032080
3 changed files with 52 additions and 9 deletions
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40
src/cluster.c
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@ -1635,16 +1635,10 @@ void clusterBuildMessageHdr(clusterMsg *hdr, int type) {
hdr->configEpoch = htonu64(master->configEpoch);
/* Set the replication offset. */
if (nodeIsSlave(myself)) {
if (server.master)
offset = server.master->reploff;
else if (server.cached_master)
offset = server.cached_master->reploff;
else
offset = 0;
} else {
if (nodeIsSlave(myself))
offset = replicationGetSlaveOffset();
else
offset = server.master_repl_offset;
}
hdr->offset = htonu64(offset);
/* Compute the message length for certain messages. For other messages
@ -1927,6 +1921,34 @@ void clusterSendFailoverAuthIfNeeded(clusterNode *node, clusterMsg *request) {
node->slaveof->voted_time = mstime();
}
/* This function returns the "rank" of this instance, a slave, in the context
* of its master-slaves ring. The rank of the slave is given by the number of
* other slaves for the same master that have a better replication offset
* compared to the local one (better means, greater, so they claim more data).
*
* A slave with rank 0 is the one with the greatest (most up to date)
* replication offset, and so forth. Note that because how the rank is computed
* multiple slaves may have the same rank, in case they have the same offset.
*
* The slave rank is used to add a delay to start an election in order to
* get voted and replace a failing master. Slaves with better replication
* offsets are more likely to win. */
int clusterGetSlaveRank(void) {
long long myoffset;
int j, rank = 0;
clusterNode *master;
redisAssert(nodeIsSlave(myself));
master = myself->slaveof;
if (master == NULL) return 0; /* Never called by slaves without master. */
myoffset = replicationGetSlaveOffset();
for (j = 0; j < master->numslaves; j++)
if (master->slaves[j] != myself &&
master->slaves[j]->repl_offset > myoffset) rank++;
return rank;
}
/* This function is called if we are a slave node and our master serving
* a non-zero amount of hash slots is in FAIL state.
*