Tweak and verify a few parameters.

Remove TODOs accordingly.

Change-Id: Ic062e13b6ae89a9135d3f14011114fe1cca1cef8

storage/local/persistence.go

@@ -43,15 +43,13 @@ const (
 	headsFormatVersion = 1
 	headsMagicString   = "PrometheusHeads"
 
-	fileBufSize = 1 << 16 // 64kiB. TODO: Tweak.
+	fileBufSize = 1 << 16 // 64kiB.
 
 	chunkHeaderLen             = 17
 	chunkHeaderTypeOffset      = 0
 	chunkHeaderFirstTimeOffset = 1
 	chunkHeaderLastTimeOffset  = 9
 
-	// TODO: Consider making any of these configurable? At least tweak
-	// them. As of now, these are educated guesses.
 	indexingMaxBatchSize  = 1024 * 1024
 	indexingBatchTimeout  = 500 * time.Millisecond // Commit batch when idle for that long.
 	indexingQueueCapacity = 1024

storage/local/storage.go

@@ -98,7 +98,7 @@ func NewMemorySeriesStorage(o *MemorySeriesStorageOptions) (Storage, error) {
 	numSeries.Set(float64(fpToSeries.length()))
 
 	return &memorySeriesStorage{
-		fpLocker:   newFingerprintLocker(100), // TODO: Tweak value.
+		fpLocker:   newFingerprintLocker(256),
 		fpToSeries: fpToSeries,
 
 		loopStopping:       make(chan struct{}),

storage/local/storage_test.go

@@ -492,7 +492,7 @@ func BenchmarkFuzz(b *testing.B) {
 	o := &MemorySeriesStorageOptions{
 		MemoryEvictionInterval:     time.Second,
 		MemoryRetentionPeriod:      10 * time.Minute,
-		PersistencePurgeInterval:   10 * time.Second,
+le		PersistencePurgeInterval:   10 * time.Second,
 		PersistenceRetentionPeriod: time.Hour,
 		PersistenceStoragePath:     directory.Path(),
 		CheckpointInterval:         3 * time.Second,