Database snapshot can be as large as 5GB. It is reasonable
to log before receiving it. Or the user might not know what
is happening and why etcd starts to use IO intensively.
streamTypeMsgApp is only used in etcd 2.0. etcd 2.3 should not talk to
etcd 2.0, either send or receive requests. So I deprecate streamTypeMsgApp
and its related stuffs from rafthttp package.
updating term is only used from streamTypeMsgApp, so it is removed too.
Use snapshotSender to send v3 snapshot message. It puts raft snapshot
message and v3 snapshot into request body, then sends it to the target peer.
When it receives http.StatusNoContent, it knows the message has been
received and processed successfully.
As receiver, snapHandler saves v3 snapshot and then processes the raft snapshot
message, then respond with http.StatusNoContent.
This PR sets etcd version and min cluster version in request header,
and let server check version compatibility. rafthttp server
will reject any message from peer with incompatible version(too low
version or too high version), and print out warning logs.
This helps etcd 2.1 connect to msgappV1 handler when the remote member
doesn't support msgappV2. And it doesn't print out unsupported handler
error to make log clean.
The original process is stopping etcd only when pipeline message finds itself
has been removed. After this PR, stream dial has this functionality too.
It helps fast etcd stop, which doesn't need to wait for stream break to
fall back to pipeline, and wait for election timeout to send out message
to detect self removal.
msgappv2 stream is used to send all MsgApp, and replaces the
functionality of msgapp stream. Compared to v1, it has several
advantanges:
1. The output message is exactly the same with the input one, which
cannot be done in v1.
2. It uses one connection to stream persistently, which prevents message
reorder and saves the time to request stream.
3. It transmits 10 addiontional bytes in the procedure of committing one
proposal, which is trivia for idle time.
4. It transmits less bytes when committing mutliple proposals or keep
committing proposals.
