The claim about unlinking the instance from the connected hash tables was the opposite of the reality. Also the current actual behavior is safer in most cases, so it is better to manually unlink when needed.
The new function is used when we want to normalize an IP address without performing a DNS lookup if the string to resolve is not a valid IP. This is useful every time only IPs are valid inputs or when we want to skip DNS resolution that is slow during runtime operations if we are required to block.
Note: the auth password with the master is voluntarily not exposed.
Masters not understanding REPLCONF ACK will reply with errors to our requests causing a number of possible issues. This commit detects a global replication offest set to -1 at the end of the replication, and marks the client representing the master with the REDIS_PRE_PSYNC flag. Note that this flag was called REDIS_PRE_PSYNC_SLAVE but now it is just REDIS_PRE_PSYNC as it is used for both slaves and masters starting with this commit. This commit fixes issue #1488.
Now the socket is closed if anetNonBlock() fails, and in general the code structure makes it harder to introduce this kind of bugs in the future. Reference: pull request #1059.
The function actually needs to be split into sub-functions at some point in the future.
There were two problems with the implementation. 1) "save" was not correctly processed when no save point was configured, as reported in issue #1416. 2) The way the code checked if an option existed in the "processed" dictionary was wrong, as we add the element with as a key associated with a NULL value, so dictFetchValue() can't be used to check for existance, but dictFind() must be used, that returns NULL only if the entry does not exist at all.
Currently replication offsets could be used into a limited way in order to understand, out of a set of slaves, what is the one with the most updated data. For example this comparison is possible of N slaves were replicating all with the same master. However the replication offset was not transferred from master to slaves (that are later promoted as masters) in any way, so for instance if there were three instances A, B, C, with A master and B and C replication from A, the following could happen: C disconnects from A. B is turned into master. A is switched to master of B. B receives some write. In this context there was no way to compare the offset of A and C, because B would use its own local master replication offset as replication offset to initialize the replication with A. With this commit what happens is that when B is turned into master it inherits the replication offset from A, making A and C comparable. In the above case assuming no inconsistencies are created during the disconnection and failover process, A will show to have a replication offset greater than C. Note that this does not mean offsets are always comparable to understand what is, in a set of instances, since in more complex examples the replica with the higher replication offset could be partitioned away when picking the instance to elect as new master. However this in general improves the ability of a system to try to pick a good replica to promote to master.
When the configured node timeout is very small, the data validity time (maximum data age for a slave to try a failover) is too little (ten times the configured node timeout) when the replication link with the master is mostly idle. In this case we'll receive some data from the master only every server.repl_ping_slave_period to refresh the last interaction with the master. This commit adds to the max data validity time the slave ping period to avoid this problem of slaves sensing too old data without a good reason. However this max data validity time is likely a setting that should be configurable by the Redis Cluster user in a way completely independent from the node timeout.
This commit makes it simple to start an handshake with a specific node address, and uses this in order to detect a node IP change and start a new handshake in order to fix the IP if possible.