Petr Gusev d79fbab682 raft: convert raft::transport_error to raft::commit_status_unknown ...

The add_entry and modify_config methods sometimes do an rpc to
execute the request on the current leader. If the tcp connection
was broken, a seastar::rpc::closed_error would be thrown to the client.
This exception was not documented in the method comments and the
client could have missed handling it. For example, this exception
was not handled when calling modify_config in raft_group0,
which sometimes broke the removenode command.

An intermittent_connection_error exception was added earlier to
solve a similar problem with the read_barrier method. In this patch it
is renamed to transport_error, as it seems to better describe the
situation, and an explicit specification for this exception
was added - the rpc implementation can throw it if it is not known
whether the call reached the target node and whether any
actions were performed on it.

In case of read_barrier it does not matter and we just retry. In case
of add_entry and modify_config we cannot retry
because the rpc calls are not idempotent, so we convert this
exception to commit_status_unknown, which the client has to handle.

Explicit comments have also been added to raft::server methods
describing all possible exceptions.

2022-10-07 13:34:16 +04:00

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