Add Queue instrumentation

queue/queue.go

@@ -1,12 +1,37 @@
 package queue
 
 import (
+	"expvar"
 	"sync"
 	"time"
 
 	"github.com/rqlite/rqlite/command"
 )
 
+// stats captures stats for the Queue.
+var stats *expvar.Map
+
+const (
+	numStatementsRx = "statements_rx"
+	numStatementsTx = "statements_tx"
+	numTimeout      = "num_timeout"
+	numFlush        = "num_flush"
+)
+
+func init() {
+	stats = expvar.NewMap("queue")
+	ResetStats()
+}
+
+// ResetStats resets the expvar stats for this module. Mostly for test purposes.
+func ResetStats() {
+	stats.Init()
+	stats.Add(numStatementsRx, 0)
+	stats.Add(numStatementsTx, 0)
+	stats.Add(numTimeout, 0)
+	stats.Add(numFlush, 0)
+}
+
 // FlushChannel is the type passed to the Queue, if caller wants
 // to know when a specific set of statements has been processed.
 type FlushChannel chan bool
@@ -110,6 +135,7 @@ func (q *Queue) Write(stmts []*command.Statement, c FlushChannel) (int64, error)
 		Statements:     stmts,
 		flushChan:      c,
 	}
+	stats.Add(numStatementsRx, int64(len(stmts)))
 	return q.seqNum, nil
 }
 
@@ -159,7 +185,11 @@ func (q *Queue) run() {
 			return
 		}
 
-		q.sendCh <- mergeQueued(queuedStmts)
+		// mergeQueued returns a new object, ownership will pass
+		// implicitly to the other side of sendCh.
+		req := mergeQueued(queuedStmts)
+		q.sendCh <- req
+		stats.Add(numStatementsTx, int64(len(req.Statements)))
 		queuedStmts = nil
 	}
 
@@ -174,9 +204,11 @@ func (q *Queue) run() {
 				writeFn()
 			}
 		case <-timer.C:
+			stats.Add(numTimeout, 1)
 			q.numTimeouts++
 			writeFn()
 		case <-q.flush:
+			stats.Add(numFlush, 1)
 			writeFn()
 		case <-q.done:
 			timer.Stop()