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scylladb / gocql

Package gocql implements a fast and robust ScyllaDB client for the Go programming language.
https://docs.scylladb.com/stable/using-scylla/drivers/cql-drivers/scylla-go-driver.html
BSD 3-Clause "New" or "Revised" License
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Document the fact that a connection string must have a fallback TCP port and not a shard-aware-one #124

Open vladzcloudius opened 1 year ago

vladzcloudius commented 1 year ago

What version of Scylla or Cassandra are you using?

2022.2.6

What version of Gocql are you using?

HEAD: e38b2bcca0a61280272806d1e2bd2b23c9749773

What version of Go are you using?

irrelevant

What did you do?

connected to the cluster providing it a connection string as host:19042 assuming this is what I need to do when I want to use a scylla shard-aware-port.

What did you expect to see?

World peace!

What did you see instead?

Not what I expected...

Description Scylla's GoCQL fork doesn't seem to have anywhere mentioned that a user is supposed to provide a not-shard-aware port in the connection string since this is the port that is going to be used as a fallback if a connection to a shard-aware-port (sent using the SUPPORTED protocol extension) fails.

This is less than obvious! Please, document this properly.

Reported by: @isburmistrov

isburmistrov commented 1 year ago

To clarify the issue here. When we're using host:19042 as a connection string, the driver assumes that this port (19042) is a non-shard aware port - it stores it into the port field of HostInfo: https://github.com/scylladb/gocql/blob/e38b2bcca0a61280272806d1e2bd2b23c9749773/control.go#L115

Later, this port can be used as a fallback option when shard-aware connection failed (https://github.com/scylladb/gocql/blob/e38b2bcca0a61280272806d1e2bd2b23c9749773/scylla.go#L658, and this addr is built here: https://github.com/scylladb/gocql/blob/e38b2bcca0a61280272806d1e2bd2b23c9749773/scylla.go#L615 using this port from HostInfo).

As a result, we can get an infinite loop of connection->fallback->reconnection because of this logic - https://github.com/scylladb/gocql/blob/e38b2bcca0a61280272806d1e2bd2b23c9749773/scylla.go#L408 - which clearly assumes that addr is either shard-aware address or a fallback. But when we used host:19042 as a connection string, both are equal.