From 2624d827fadc604323db979e1d7b59415531f3d3 Mon Sep 17 00:00:00 2001
From: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
Date: Wed, 21 Oct 2020 18:27:13 +0530
Subject: [PATCH] Read repair empty last file in chunks_head (#8061)

* Read repair empty file in chunks_head

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Refactor and introduce repairLastChunkFile

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Attempt windows test fix

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Fix review comments

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Fix review comments

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>
---
 tsdb/chunks/head_chunks.go      | 36 +++++++++++++++++
 tsdb/chunks/head_chunks_test.go | 70 +++++++++++++++++++++++++++++++++
 2 files changed, 106 insertions(+)

diff --git a/tsdb/chunks/head_chunks.go b/tsdb/chunks/head_chunks.go
index 632682218..154149d0c 100644
--- a/tsdb/chunks/head_chunks.go
+++ b/tsdb/chunks/head_chunks.go
@@ -167,6 +167,11 @@ func (cdm *ChunkDiskMapper) openMMapFiles() (returnErr error) {
 		return err
 	}
 
+	files, err = repairLastChunkFile(files)
+	if err != nil {
+		return err
+	}
+
 	chkFileIndices := make([]int, 0, len(files))
 	for seq, fn := range files {
 		f, err := fileutil.OpenMmapFile(fn)
@@ -226,9 +231,40 @@ func listChunkFiles(dir string) (map[int]string, error) {
 		}
 		res[int(seq)] = filepath.Join(dir, fi.Name())
 	}
+
 	return res, nil
 }
 
+// repairLastChunkFile deletes the last file if it's empty.
+// Because we don't fsync when creating these file, we could end
+// up with an empty file at the end during an abrupt shutdown.
+func repairLastChunkFile(files map[int]string) (_ map[int]string, returnErr error) {
+	lastFile := -1
+	for seq := range files {
+		if seq > lastFile {
+			lastFile = seq
+		}
+	}
+
+	if lastFile <= 0 {
+		return files, nil
+	}
+
+	info, err := os.Stat(files[lastFile])
+	if err != nil {
+		return files, errors.Wrap(err, "file stat during last head chunk file repair")
+	}
+	if info.Size() == 0 {
+		// Corrupt file, hence remove it.
+		if err := os.RemoveAll(files[lastFile]); err != nil {
+			return files, errors.Wrap(err, "delete corrupted, empty head chunk file during last file repair")
+		}
+		delete(files, lastFile)
+	}
+
+	return files, nil
+}
+
 // WriteChunk writes the chunk to the disk.
 // The returned chunk ref is the reference from where the chunk encoding starts for the chunk.
 func (cdm *ChunkDiskMapper) WriteChunk(seriesRef uint64, mint, maxt int64, chk chunkenc.Chunk) (chkRef uint64, err error) {
diff --git a/tsdb/chunks/head_chunks_test.go b/tsdb/chunks/head_chunks_test.go
index bfb4262ad..f8ed26cf1 100644
--- a/tsdb/chunks/head_chunks_test.go
+++ b/tsdb/chunks/head_chunks_test.go
@@ -19,6 +19,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"strconv"
 	"testing"
 
 	"github.com/prometheus/prometheus/tsdb/chunkenc"
@@ -363,6 +364,75 @@ func TestHeadReadWriter_TruncateAfterFailedIterateChunks(t *testing.T) {
 	testutil.Ok(t, hrw.Truncate(2000))
 }
 
+func TestHeadReadWriter_ReadRepairOnEmptyLastFile(t *testing.T) {
+	hrw := testHeadReadWriter(t)
+	defer func() {
+		testutil.Ok(t, hrw.Close())
+	}()
+
+	timeRange := 0
+	addChunk := func() {
+		step := 100
+		mint, maxt := timeRange+1, timeRange+step-1
+		_, err := hrw.WriteChunk(1, int64(mint), int64(maxt), randomChunk(t))
+		testutil.Ok(t, err)
+		timeRange += step
+	}
+	nonEmptyFile := func() {
+		testutil.Ok(t, hrw.CutNewFile())
+		addChunk()
+	}
+
+	addChunk()     // 1. Created with the first chunk.
+	nonEmptyFile() // 2.
+	nonEmptyFile() // 3.
+
+	testutil.Equals(t, 3, len(hrw.mmappedChunkFiles))
+	lastFile := 0
+	for idx := range hrw.mmappedChunkFiles {
+		if idx > lastFile {
+			lastFile = idx
+		}
+	}
+	testutil.Equals(t, 3, lastFile)
+	dir := hrw.dir.Name()
+	testutil.Ok(t, hrw.Close())
+
+	// Write an empty last file mimicking an abrupt shutdown on file creation.
+	emptyFileName := segmentFile(dir, lastFile+1)
+	f, err := os.OpenFile(emptyFileName, os.O_WRONLY|os.O_CREATE, 0666)
+	testutil.Ok(t, err)
+	testutil.Ok(t, f.Sync())
+	stat, err := f.Stat()
+	testutil.Ok(t, err)
+	testutil.Equals(t, int64(0), stat.Size())
+	testutil.Ok(t, f.Close())
+
+	// Open chunk disk mapper again, corrupt file should be removed.
+	hrw, err = NewChunkDiskMapper(dir, chunkenc.NewPool())
+	testutil.Ok(t, err)
+	testutil.Assert(t, !hrw.fileMaxtSet, "")
+	testutil.Ok(t, hrw.IterateAllChunks(func(_, _ uint64, _, _ int64, _ uint16) error { return nil }))
+	testutil.Assert(t, hrw.fileMaxtSet, "")
+
+	// Removed from memory.
+	testutil.Equals(t, 3, len(hrw.mmappedChunkFiles))
+	for idx := range hrw.mmappedChunkFiles {
+		testutil.Assert(t, idx <= lastFile, "file index is bigger than previous last file")
+	}
+
+	// Removed even from disk.
+	files, err := ioutil.ReadDir(dir)
+	testutil.Ok(t, err)
+	testutil.Equals(t, 3, len(files))
+	for _, fi := range files {
+		seq, err := strconv.ParseUint(fi.Name(), 10, 64)
+		testutil.Ok(t, err)
+		testutil.Assert(t, seq <= uint64(lastFile), "file index on disk is bigger than previous last file")
+	}
+
+}
+
 func testHeadReadWriter(t *testing.T) *ChunkDiskMapper {
 	tmpdir, err := ioutil.TempDir("", "data")
 	testutil.Ok(t, err)