Support configurable snapshot thresholds

CHANGELOG.md

@@ -1,4 +1,5 @@
 ## 3.3.0 (unreleased)
+- [PR #149](https://github.com/rqlite/rqlite/pull/149): Support configurable Raft snapshot thresholds.
 - [PR #148](https://github.com/rqlite/rqlite/pull/148): Support pprof information over HTTP.
 
 ## 3.2.1 (May 22nd 2016)

cmd/rqlited/main.go

@@ -77,6 +77,7 @@ var pprofEnabled bool
 var dsn string
 var onDisk bool
 var noVerifySelect bool
+var raftSnapThreshold uint64
 var showVersion bool
 var cpuprofile string
 
@@ -98,6 +99,7 @@ func init() {
 	flag.BoolVar(&onDisk, "ondisk", false, "Use an on-disk SQLite database")
 	flag.BoolVar(&noVerifySelect, "nosel", false, "Don't verify that all queries begin with SELECT")
 	flag.BoolVar(&showVersion, "version", false, "Show version information and exit")
+	flag.Uint64Var(&raftSnapThreshold, "raftsnap", 8192, "Number of outstanding log entries to trigger snapshot")
 	flag.StringVar(&cpuprofile, "cpuprofile", "", "Write CPU profile to file")
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "\n%s\n\n", desc)
@@ -186,6 +188,7 @@ func main() {
 	if err := store.Open(joinAddr == ""); err != nil {
 		log.Fatalf("failed to open store: %s", err.Error())
 	}
+	store.SnapshotThreshold = raftSnapThreshold
 
 	// Create and configure cluster service.
 	tn := mux.Listen(muxMetaHeader)

doc/DESIGN.md

@@ -28,4 +28,4 @@ The diagram below shows a high-level view of a rqlite node.
                  └───────────────────────────────────────────────┘
 
 ## Log Compaction
-rqlite automatically performs log compaction. After a fixed number of changes rqlite snapshots the SQLite database, and truncates the Raft log. This is a technical feature of the Raft consensus system, and most users of rqlite need not be concerned with this.
+rqlite automatically performs log compaction. After a configurable number of changes rqlite snapshots the SQLite database, and truncates the Raft log. This is a technical feature of the Raft consensus system, and most users of rqlite need not be concerned with this.

store/store.go

@@ -163,6 +163,8 @@ type Store struct {
 	meta   *clusterMeta
 
 	logger *log.Logger
+
+	SnapshotThreshold uint64
 }
 
 // New returns a new Store.
@@ -208,6 +210,9 @@ func (s *Store) Open(enableSingle bool) error {
 
 	// Setup Raft configuration.
 	config := raft.DefaultConfig()
+	if s.SnapshotThreshold != 0 {
+		config.SnapshotThreshold = s.SnapshotThreshold
+	}
 
 	// Check for any existing peers.
 	peers, err := readPeersJSON(filepath.Join(s.raftDir, "peers.json"))