Does etcd cache data locally

[ishan...@go-mmt.com]

Hi,

I have been going through the documentation and though the slides explaining the Raft algorithm do suggest that etcd does keeps local copies of data, which are kept in sync among the various nodes in the cluster.

I was wondering if there is any documentation that points to this as a fact. What I really want to know is:

1. Let's assume all nodes are properly synced and each node has all the updated KV pairs.

2. If I do a key lookup on any one node locally, it should not result in any Network I/O

3. Although etcd might do network I/O to keep data in sync, but my code which is frequently reading KV pairs from etcd locally would avoid a lot of network I/O

Do I understand this flow correctly?

Regards,

Ishan

[Jingyi Hu]

Roughly speaking, local node needs to communicate with leader node (via network I/O) to find out if it the requested key is still in sync before it serves the request.

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[Jingyi Hu]

Sorry I was assuming you are doing linearizable [1] read. For serializalible read, local node can serve locally (no network I/O).

Ref: [1] https://en.wikipedia.org/wiki/Linearizability

[Jingyi Hu]

For more description of the request flow, please refer to section 6.4 in raft paper. You can find the corresponding implementation in https://github.com/etcd-io/etcd/blob/master/raft/raft.go