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RedisCluster that can use ReadOnly slaves
JedisCluster uses only Master nodes in the cluster, all the Slave nodes are only standby nodes. In many situation this is a waste of resources.
So I write an EnhancedJedisClusterInfoCache besides the original JedisClusterInfoCache. When we want to read only from Master, JedisCluster will use JedisClusterInfoCache, nearly nothing changed. But if we want to read from Slave or both Master and Slave nodes, JedisClusterConnectionHandler will create an EnhancedJedisClusterInfoCache.
In the new cache class, there are two maps, one for master nodes and the other for slave nodes. All the Jedis instances in the slave pool have been sent a ReadOnly command when they were created.
When renewing the slot cache (master goes down or slot migration), both of the two maps will be reset, the JedisPool will be destroyed. So we don't need to worry about writing to a ReadOnly node.
Thanks for reviewing my codes.
P.S. I've read #790 #830 and some other posts and issues about ReadOnly slaves. And my thought is definitely same with @marcosnils mentioned in #1522 .
Can anybody else review this PR? @marcosnils @sazzad16 can you help? Thank you.
To everyone who have asked about merging this PR, first of all I thank you all for your interest in Jedis.
This PR has a few backward incompatible parts which wouldn't allow a smooth transition from one version to another for the users who have codes based on the concerned classes. So this specific PR is unlikely to be merged.
We have kept open this PR hoping that someone would pick-up the idea and craft another PR with not so backward incompatible parts or at least with "salvageable" ones.
Thanks again.
@sazzad16 can you please elaborate more on backward-incompatible changes? I've spotted only JedisClusterConnectionHandler. Since this was introduced before v4.x, is there an existing way already to be able to read from replicas in readonly mode?
Btw looks like by PR JedisCluster / BinaryJedisCluster / JedisClusterConnectionHandler / JedisFactory require using builder pattern for extendibility, which will require.. a breaking change
@sazzad16 can you please elaborate more on backward-incompatible changes? That way I could try to offer a new PR with less breaking changes. Thanks!
@esigma5 @eugeniyk Just try not to remove too many public methods and public classes and/or change their behavior with current parameters.
PS: We have started publishing alpha releases for Jedis 5.0. Now is a very good time to work on things that may have breaking parts. Also, if you have something promising please let us know, preferably as WIP or POC, in case we want to wait.
@eugeniyk Sincere apologies I missed your comment above.
