Add metrics for WAL compression

Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>

wal/wal.go

@@ -169,12 +169,14 @@ type WAL struct {
 	compress    bool
 	snappyBuf   []byte
 
-	fsyncDuration   prometheus.Summary
-	pageFlushes     prometheus.Counter
-	pageCompletions prometheus.Counter
-	truncateFail    prometheus.Counter
-	truncateTotal   prometheus.Counter
-	currentSegment  prometheus.Gauge
+	fsyncDuration        prometheus.Summary
+	pageFlushes          prometheus.Counter
+	pageCompletions      prometheus.Counter
+	truncateFail         prometheus.Counter
+	truncateTotal        prometheus.Counter
+	currentSegment       prometheus.Gauge
+	recordRawSize        prometheus.Counter
+	recordCompressedSize prometheus.Counter
 }
 
 // New returns a new WAL over the given directory.
@@ -227,8 +229,16 @@ func NewSize(logger log.Logger, reg prometheus.Registerer, dir string, segmentSi
 		Name: "prometheus_tsdb_wal_segment_current",
 		Help: "WAL segment index that TSDB is currently writing to.",
 	})
+	w.recordRawSize = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "prometheus_tsdb_wal_raw_record_bytes_total",
+		Help: "The total number of bytes received by the WAL.",
+	})
+	w.recordCompressedSize = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "prometheus_tsdb_wal_compressed_record_bytes_total",
+		Help: "The total size of records after having been compressed.",
+	})
 	if reg != nil {
-		reg.MustRegister(w.fsyncDuration, w.pageFlushes, w.pageCompletions, w.truncateFail, w.truncateTotal, w.currentSegment)
+		reg.MustRegister(w.fsyncDuration, w.pageFlushes, w.pageCompletions, w.truncateFail, w.truncateTotal, w.currentSegment, w.recordRawSize, w.recordCompressedSize)
 	}
 
 	_, j, err := w.Segments()
@@ -539,6 +549,7 @@ func (w *WAL) log(rec []byte, final bool) error {
 	}
 
 	compressed := false
+	w.recordRawSize.Add(float64(len(rec)))
 	if w.compress && len(rec) > 0 {
 		// Allow Snappy to use the full capacity of the buffer.
 		w.snappyBuf = w.snappyBuf[:cap(w.snappyBuf)]
@@ -548,6 +559,7 @@ func (w *WAL) log(rec []byte, final bool) error {
 			compressed = true
 		}
 	}
+	w.recordCompressedSize.Add(float64(len(rec)))
 
 	// Populate as many pages as necessary to fit the record.
 	// Be careful to always do one pass to ensure we write zero-length records.