Add streaming stats to bolt bench.

This commit adds -stats-interval to the 'bolt bench' utility. By setting this argument
to an interval greater than 0s, the benchmark tool will output stats as streaming JSON.
This data can, in turn, be graphed to understand performance over time.

2 files changed, 61 insertions, 23 deletions

diff --git a/cmd/bolt/bench.go b/cmd/bolt/bench.go
index 10a5599..fef8e54 100644
--- a/cmd/bolt/bench.go
+++ b/cmd/bolt/bench.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io/ioutil"
@@ -42,6 +43,11 @@ func Bench(options *BenchOptions) {
 	}
 	defer db.Close()
 
+	// Enable streaming stats.
+	if options.StatsInterval > 0 {
+		go printStats(db, options.StatsInterval)
+	}
+
 	// Start profiling for writes.
 	if options.ProfileMode == "rw" || options.ProfileMode == "w" {
 		benchStartProfiling(options)
@@ -73,9 +79,9 @@ func Bench(options *BenchOptions) {
 	}
 
 	// Print results.
-	fmt.Printf("# Write\t%v\t(%v/op)\t(%v op/sec)\n", results.WriteDuration, results.WriteOpDuration(), results.WriteOpsPerSecond())
-	fmt.Printf("# Read\t%v\t(%v/op)\t(%v op/sec)\n", results.ReadDuration, results.ReadOpDuration(), results.ReadOpsPerSecond())
-	fmt.Println("")
+	fmt.Fprintf(os.Stderr, "# Write\t%v\t(%v/op)\t(%v op/sec)\n", results.WriteDuration, results.WriteOpDuration(), results.WriteOpsPerSecond())
+	fmt.Fprintf(os.Stderr, "# Read\t%v\t(%v/op)\t(%v op/sec)\n", results.ReadDuration, results.ReadOpDuration(), results.ReadOpsPerSecond())
+	fmt.Fprintln(os.Stderr, "")
 }
 
 // Writes to the database.
@@ -233,18 +239,42 @@ func benchStopProfiling() {
 	}
 }
 
+// Continuously prints stats on the database at given intervals.
+func printStats(db *bolt.DB, interval time.Duration) {
+	var prevStats = db.Stats()
+	var encoder = json.NewEncoder(os.Stdout)
+
+	for {
+		// Wait for the stats interval.
+		time.Sleep(interval)
+
+		// Retrieve new stats and find difference from previous iteration.
+		var stats = db.Stats()
+		var diff = stats.Sub(&prevStats)
+
+		// Print as JSON to STDOUT.
+		if err := encoder.Encode(diff); err != nil {
+			fatal(err)
+		}
+
+		// Save stats for next iteration.
+		prevStats = stats
+	}
+}
+
 // BenchOptions represents the set of options that can be passed to Bench().
 type BenchOptions struct {
-	ProfileMode  string
-	WriteMode    string
-	ReadMode     string
-	Iterations   int
-	BatchSize    int
-	KeySize      int
-	ValueSize    int
-	CPUProfile   string
-	MemProfile   string
-	BlockProfile string
+	ProfileMode   string
+	WriteMode     string
+	ReadMode      string
+	Iterations    int
+	BatchSize     int
+	KeySize       int
+	ValueSize     int
+	CPUProfile    string
+	MemProfile    string
+	BlockProfile  string
+	StatsInterval time.Duration
 }
 
 // BenchResults represents the performance results of the benchmark.
diff --git a/cmd/bolt/main.go b/cmd/bolt/main.go
index cb2d47a..3558500 100644
--- a/cmd/bolt/main.go
+++ b/cmd/bolt/main.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"time"
 
 	"github.com/codegangsta/cli"
 )
@@ -104,19 +105,26 @@ func NewApp() *cli.App {
 				&cli.StringFlag{Name: "cpuprofile", Usage: "CPU profile output path"},
 				&cli.StringFlag{Name: "memprofile", Usage: "Memory profile output path"},
 				&cli.StringFlag{Name: "blockprofile", Usage: "Block profile output path"},
+				&cli.StringFlag{Name: "stats-interval", Value: "0s", Usage: "Continuous stats interval"},
 			},
 			Action: func(c *cli.Context) {
+				statsInterval, err := time.ParseDuration(c.String("stats-interval"))
+				if err != nil {
+					fatal(err)
+				}
+
 				Bench(&BenchOptions{
-					ProfileMode:  c.String("profile-mode"),
-					WriteMode:    c.String("write-mode"),
-					ReadMode:     c.String("read-mode"),
-					Iterations:   c.Int("count"),
-					BatchSize:    c.Int("batch-size"),
-					KeySize:      c.Int("key-size"),
-					ValueSize:    c.Int("value-size"),
-					CPUProfile:   c.String("cpuprofile"),
-					MemProfile:   c.String("memprofile"),
-					BlockProfile: c.String("blockprofile"),
+					ProfileMode:   c.String("profile-mode"),
+					WriteMode:     c.String("write-mode"),
+					ReadMode:      c.String("read-mode"),
+					Iterations:    c.Int("count"),
+					BatchSize:     c.Int("batch-size"),
+					KeySize:       c.Int("key-size"),
+					ValueSize:     c.Int("value-size"),
+					CPUProfile:    c.String("cpuprofile"),
+					MemProfile:    c.String("memprofile"),
+					BlockProfile:  c.String("blockprofile"),
+					StatsInterval: statsInterval,
 				})
 			},
 		}}