This PR introduces new node-discovery integration with Consul and etcd. By using one of those systems with rqlite, automatic clustering of rqlite is much easier.
This is a breaking change. However this feature hasn't been tested and
allows end-users to break the system too easily. Low-level control over
the SQLite database is better done with PRAGMA commands where possible.
Before Raft truncates the log, it needs to retrieve a snapshot of the SQLite database to represent the log entries that are removed during that truncation. Raft then writes that snapshot to disk. To reduce both disk IO and disk space this change compresses that SQLite snapshot before it is written to disk, and decompresses it during a restore operation.
This change also deals with older SQLite snapshots, which were not compressed.
This PR changes Raft Log Entry encoding from JSON to Protobuf. Furthermore, larger Raft commands (which can result from batching SQL statements, or individually long SQL statements) are compressed before encoding.
This primary reason for this change is to reduce IO load since that is one of the largest performance bottlenecks. It will also reduce internode traffic.
Legacy JSON-encoded commands are still handled by this code, so this change is backwards-compatible with previous releases in the v5 series.
This change allows the read request to specify the maximum time the node
receiving the request may have last heard from the cluster leader. It
only applies to a read consistency selection of None.
Philip O'Toole
wangfenjin