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Increase successful psync chance by flushing pending replication stream

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before disconnecting replica.

To perform manual failover without data loss, we execute following
steps:

1. Temporarily disable write by executing `replica of 127.0.0.1 0` on
the master
2. Promote one replica as the new master.
3. Set the old master as a replica of the promoted master.

During step 1, the master disconnects replicas. If there are pending
replication streams for the replica that is promoted as the new master
in step 2, step 3 fails to psync because the old master has a more
recent replication stream.

This patch improves the chances of successful psync by flushing the
pending replication stream of the replica in a non-blocking manner
during step 1. This ensures that the replica promoted in step 2 is more
likely to have the same replication stream as the master, increasing the
likelihood of successful psync in step 3.
This commit is contained in:
sr_zhao 2024-11-13 14:56:48 +08:00
parent cf83803880
commit 13c2f7adbb
1 changed files with 11 additions and 1 deletions
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12
src/networking.c
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@ -1461,7 +1461,17 @@ void disconnectSlaves(void) {
listNode *ln;
listRewind(server.slaves,&li);
while((ln = listNext(&li))) {
freeClient((client*)ln->value);
/* Attempt to flush pending replication stream before disconnecting
* slaves without blocking, increasing the chances of successful
* psync for slaves when failed over. */
client *slave = (client*)ln->value;
writeToClient(slave,0);
if (clientHasPendingReplies(slave)) {
sds client_desc = catClientInfoString(sdsempty(), slave);
serverLog(LL_NOTICE, "Slave still have pending replies when disconnect: %s", client_desc);
sdsfree(client_desc);
}
freeClient(slave);
}
}