repair + compact: Improved logging for easier future debug purposes.

This is based on my experience while debugging https://github.com/prometheus/prometheus/issues/3943.

I needed to deduct few things, and all that would be just bit easier with these two logs:
- new block's ULID on each compaction.
- actual list of Blocks (ulid + time range) on Prometheus startup (easy to log that while repairing blocks).

We don't really need blocks that takes part in compaction - that can be deducted easily based on time ranges of blocks we have currently in system.

What do you think?

Signed-off-by: Bartek Plotka <bwplotka@gmail.com>

compact.go

@@ -14,6 +14,7 @@
 package tsdb
 
 import (
+	"fmt"
 	"io"
 	"math/rand"
 	"os"
@@ -33,7 +34,7 @@ import (
 	"github.com/prometheus/tsdb/labels"
 )
 
-// ExponentialBlockRanges returns the time ranges based on the stepSize
+// ExponentialBlockRanges returns the time ranges based on the stepSize.
 func ExponentialBlockRanges(minSize int64, steps, stepSize int) []int64 {
 	ranges := make([]int64, 0, steps)
 	curRange := minSize
@@ -312,9 +313,12 @@ func compactBlockMetas(uid ulid.ULID, blocks ...*BlockMeta) *BlockMeta {
 // Compact creates a new block in the compactor's directory from the blocks in the
 // provided directories.
 func (c *LeveledCompactor) Compact(dest string, dirs ...string) (uid ulid.ULID, err error) {
-	var blocks []BlockReader
-	var bs []*Block
-	var metas []*BlockMeta
+	var (
+		blocks []BlockReader
+		bs     []*Block
+		metas  []*BlockMeta
+		uids   []string
+	)
 
 	for _, d := range dirs {
 		b, err := OpenBlock(d, c.chunkPool)
@@ -331,13 +335,23 @@ func (c *LeveledCompactor) Compact(dest string, dirs ...string) (uid ulid.ULID,
 		metas = append(metas, meta)
 		blocks = append(blocks, b)
 		bs = append(bs, b)
+		uids = append(uids, meta.ULID.String())
 	}
 
 	entropy := rand.New(rand.NewSource(time.Now().UnixNano()))
 	uid = ulid.MustNew(ulid.Now(), entropy)
 
-	err = c.write(dest, compactBlockMetas(uid, metas...), blocks...)
+	meta := compactBlockMetas(uid, metas...)
+	err = c.write(dest, meta, blocks...)
 	if err == nil {
+		level.Info(c.logger).Log(
+			"msg", "compact blocks",
+			"count", len(blocks),
+			"mint", meta.MinTime,
+			"maxt", meta.MaxTime,
+			"ulid", meta.ULID,
+			"sources", fmt.Sprintf("%v", uids),
+		)
 		return uid, nil
 	}
 
@@ -365,7 +379,13 @@ func (c *LeveledCompactor) Write(dest string, b BlockReader, mint, maxt int64) (
 	meta.Compaction.Level = 1
 	meta.Compaction.Sources = []ulid.ULID{uid}
 
-	return uid, c.write(dest, meta, b)
+	err := c.write(dest, meta, b)
+	if err != nil {
+		return uid, err
+	}
+
+	level.Info(c.logger).Log("msg", "write block", "mint", meta.MinTime, "maxt", meta.MaxTime, "ulid", meta.ULID)
+	return uid, nil
 }
 
 // instrumentedChunkWriter is used for level 1 compactions to record statistics
@@ -390,8 +410,6 @@ func (w *instrumentedChunkWriter) WriteChunks(chunks ...chunks.Meta) error {
 // write creates a new block that is the union of the provided blocks into dir.
 // It cleans up all files of the old blocks after completing successfully.
 func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockReader) (err error) {
-	level.Info(c.logger).Log("msg", "compact blocks", "count", len(blocks), "mint", meta.MinTime, "maxt", meta.MaxTime)
-
 	dir := filepath.Join(dest, meta.ULID.String())
 	tmp := dir + ".tmp"
 
@@ -472,7 +490,7 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 		return errors.Wrap(err, "sync temporary dir file")
 	}
 
-	// close temp dir before rename block dir(for windows platform)
+	// Close temp dir before rename block dir (for windows platform).
 	if err = df.Close(); err != nil {
 		return errors.Wrap(err, "close temporary dir")
 	}
@@ -482,6 +500,7 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 	if err := renameFile(tmp, dir); err != nil {
 		return errors.Wrap(err, "rename block dir")
 	}
+
 	return nil
 }
 
@@ -718,11 +737,6 @@ type compactionMerger struct {
 	intervals Intervals
 }
 
-type compactionSeries struct {
-	labels labels.Labels
-	chunks []*chunks.Meta
-}
-
 func newCompactionMerger(a, b ChunkSeriesSet) (*compactionMerger, error) {
 	c := &compactionMerger{
 		a: a,

repair.go

@@ -36,9 +36,20 @@ func repairBadIndexVersion(logger log.Logger, dir string) error {
 			return err
 		}
 		if meta.Version == 1 {
+			level.Info(logger).Log(
+				"msg", "found healthy block",
+				"mint", meta.MinTime,
+				"maxt", meta.MaxTime,
+				"ulid", meta.ULID,
+			)
 			continue
 		}
-		level.Info(logger).Log("msg", "fixing broken block", "ulid", meta.ULID)
+		level.Info(logger).Log(
+			"msg", "fixing broken block",
+			"mint", meta.MinTime,
+			"maxt", meta.MaxTime,
+			"ulid", meta.ULID,
+		)
 
 		repl, err := os.Create(filepath.Join(d, "index.repaired"))
 		if err != nil {