clickhouse-cpp Add list of hosts with ports for setting connection

Add list of hosts with ports for setting connection

Open df530 opened this issue 3 years ago • 5 comments

It is possible to specify multiple hosts to connect to. It approves fault tolerance of connection because when one host isn't alive client can try to connect to another one. The connection will be set to the first available host.

Client client(ClientOptions()
              .SetHost({
                  ClientOptions::HostPort("host1.com", 8000),
                  ClientOptions::HostPort("host2.com"), /// port is ClientOptions.port
              }));

When ResetConnection is called, it tries to connect to the first host. If connection failed, then it tries to connect to the next host in list, while list doesn't end up (round-robin approach). If list ends up, ResetConnection throws exception of last host.

Jan 11 '22 17:01 df530

All committers have signed the CLA.

Jan 11 '22 17:01 CLAassistant

Looks good to me. I think it's better to merge commits in one. And providing more information about the reasons for commit (fault tolerance) and about the implementation (round robin) in pull request description would be great

Jan 19 '22 21:01 PolyProgrammist

The idea/motivation is clean. Maybe it would be clearer to push that logic a bit deeper?

Here we have iteration through different IPs which can be extracted from the same domain name: https://github.com/ClickHouse/clickhouse-cpp/blob/b36c87fb6f09376f71fbda671cae4c754afc7ea4/clickhouse/base/socket.cpp#L87-L88

Maybe we can generalize that code a bit for multiple hosts/ports cases instead of creating one more retry loop outside?

In that case, connect timeouts should work better.