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Sentinel: various fixes to leader election implementation.

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antirez 2013-11-19 16:20:42 +01:00
parent 1f9728cb20
commit b22d1beea0
1 changed files with 41 additions and 29 deletions
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70
src/sentinel.c
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@ -2672,7 +2672,7 @@ void sentinelAskMasterStateToOtherSentinels(sentinelRedisInstance *master, int f
* voted for the specifed 'req_epoch' or one greater.
*
* If a vote is not available returns NULL, otherwise return the Sentinel
* runid and populate the leader_epoch with the epoch of the last vote. */
* runid and populate the leader_epoch with the epoch of the vote. */
char *sentinelVoteLeader(sentinelRedisInstance *master, uint64_t req_epoch, char *req_runid, uint64_t *leader_epoch) {
if (req_epoch > sentinel.current_epoch) {
sentinel.current_epoch = req_epoch;
@ -2680,7 +2680,8 @@ char *sentinelVoteLeader(sentinelRedisInstance *master, uint64_t req_epoch, char
(unsigned long long) sentinel.current_epoch);
}
if (master->leader_epoch < req_epoch && sentinel.current_epoch <= req_epoch) {
if (master->leader_epoch < req_epoch && sentinel.current_epoch <= req_epoch)
{
sdsfree(master->leader);
master->leader = sdsnew(req_runid);
master->leader_epoch = sentinel.current_epoch;
@ -2692,7 +2693,8 @@ char *sentinelVoteLeader(sentinelRedisInstance *master, uint64_t req_epoch, char
*
* The random addition is useful to desynchronize a bit the slaves
* and reduce the chance that no slave gets majority. */
master->failover_start_time = mstime() + rand() % 2000;
if (strcasecmp(master->leader,server.runid))
master->failover_start_time = mstime() + rand() % 2000;
}
*leader_epoch = master->leader_epoch;
@ -2706,17 +2708,19 @@ struct sentinelLeader {
/* Helper function for sentinelGetLeader, increment the counter
* relative to the specified runid. */
void sentinelLeaderIncr(dict *counters, char *runid) {
int sentinelLeaderIncr(dict *counters, char *runid) {
dictEntry *de = dictFind(counters,runid);
uint64_t oldval;
if (de) {
oldval = dictGetUnsignedIntegerVal(de);
dictSetUnsignedIntegerVal(de,oldval+1);
return oldval+1;
} else {
de = dictAddRaw(counters,runid);
redisAssert(de != NULL);
dictSetUnsignedIntegerVal(de,1);
return 1;
}
}
@ -2734,49 +2738,57 @@ char *sentinelGetLeader(sentinelRedisInstance *master, uint64_t epoch) {
char *myvote;
char *winner = NULL;
uint64_t leader_epoch;
uint64_t max_votes = 0;
redisAssert(master->flags & (SRI_O_DOWN|SRI_FAILOVER_IN_PROGRESS));
counters = dictCreate(&leaderVotesDictType,NULL);
/* Count my vote (and vote for myself if I still did not voted for
* the currnet epoch). */
myvote = sentinelVoteLeader(master,epoch,server.runid,&leader_epoch);
if (myvote && leader_epoch == epoch) {
sentinelLeaderIncr(counters,myvote);
voters++;
}
/* Count other sentinels votes */
di = dictGetIterator(master->sentinels);
while((de = dictNext(di)) != NULL) {
sentinelRedisInstance *ri = dictGetVal(de);
if (ri->leader == NULL || ri->leader_epoch != sentinel.current_epoch)
continue;
sentinelLeaderIncr(counters,ri->leader);
if (ri->leader != NULL && ri->leader_epoch == sentinel.current_epoch)
sentinelLeaderIncr(counters,ri->leader);
voters++;
}
dictReleaseIterator(di);
voters_quorum = voters/2+1;
/* Check what's the winner. For the winner to win, it needs two conditions:
* 1) Absolute majority between voters (50% + 1).
* 2) And anyway at least master->quorum votes. */
{
uint64_t max_votes = 0; /* Max votes so far. */
di = dictGetIterator(counters);
while((de = dictNext(di)) != NULL) {
uint64_t votes = dictGetUnsignedIntegerVal(de);
di = dictGetIterator(counters);
while((de = dictNext(di)) != NULL) {
uint64_t votes = dictGetUnsignedIntegerVal(de);
if (max_votes < votes) {
max_votes = votes;
winner = dictGetKey(de);
}
if (votes > max_votes) {
max_votes = votes;
winner = dictGetKey(de);
}
dictReleaseIterator(di);
if (winner && (max_votes < voters_quorum || max_votes < master->quorum))
winner = NULL;
}
dictReleaseIterator(di);
/* Count this Sentinel vote:
* if this Sentinel did not voted yet, either vote for the most
* common voted sentinel, or for itself if no vote exists at all. */
if (winner)
myvote = sentinelVoteLeader(master,epoch,winner,&leader_epoch);
else
myvote = sentinelVoteLeader(master,epoch,server.runid,&leader_epoch);
if (myvote && leader_epoch == epoch) {
uint64_t votes = sentinelLeaderIncr(counters,myvote);
if (votes > max_votes) {
max_votes = votes;
winner = myvote;
}
}
voters++; /* Anyway, count me as one of the voters. */
voters_quorum = voters/2+1;
if (winner && (max_votes < voters_quorum || max_votes < master->quorum))
winner = NULL;
winner = winner ? sdsnew(winner) : NULL;
sdsfree(myvote);
dictRelease(counters);