index cache: Cache expanded postings (thanos-io#6420)

* cache expanded postings in index cache Signed-off-by: Ben Ye <benye@amazon.com> * update changelog Signed-off-by: Ben Ye <benye@amazon.com> * fix Signed-off-by: Ben Ye <benye@amazon.com> * fix lint Signed-off-by: Ben Ye <benye@amazon.com> * rebase main and added compression name to key Signed-off-by: Ben Ye <benye@amazon.com> * update key Signed-off-by: Ben Ye <benye@amazon.com> * add e2e test for memcached Signed-off-by: Ben Ye <benye@amazon.com> * fix cache config Signed-off-by: Ben Ye <benye@amazon.com> * address review comments Signed-off-by: Ben Ye <benye@amazon.com> --------- Signed-off-by: Ben Ye <benye@amazon.com>
databricks · Jun 27, 2023 · 4e69ba7 · 4e69ba7
1 parent 9d99834
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Showing 14 changed files with 521 additions and 61 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -21,6 +21,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6163](https://github.com/thanos-io/thanos/pull/6163) Receiver: Add hidden flag `--receive-forward-max-backoff` to configure the max backoff for forwarding requests.
 - [#5777](https://github.com/thanos-io/thanos/pull/5777) Receive: Allow specifying tenant-specific external labels in Router Ingestor.
 - [#6352](https://github.com/thanos-io/thanos/pull/6352) Store: Expose store gateway query stats in series response hints.
+- [#6420](https://github.com/thanos-io/thanos/pull/6420) Index Cache: Cache expanded postings.
 
 ### Fixed
 - [#6427](https://github.com/thanos-io/thanos/pull/6427) Receive: increasing log level for failed uploads to error

diff --git a/pkg/store/bucket.go b/pkg/store/bucket.go
@@ -379,6 +379,11 @@ func (noopCache) FetchMultiPostings(_ context.Context, _ ulid.ULID, keys []label
 	return map[labels.Label][]byte{}, keys
 }
 
+func (noopCache) StoreExpandedPostings(_ ulid.ULID, _ []*labels.Matcher, _ []byte) {}
+func (noopCache) FetchExpandedPostings(_ context.Context, _ ulid.ULID, _ []*labels.Matcher) ([]byte, bool) {
+	return []byte{}, false
+}
+
 func (noopCache) StoreSeries(ulid.ULID, storage.SeriesRef, []byte) {}
 func (noopCache) FetchMultiSeries(_ context.Context, _ ulid.ULID, ids []storage.SeriesRef) (map[storage.SeriesRef][]byte, []storage.SeriesRef) {
 	return map[storage.SeriesRef][]byte{}, ids
@@ -2185,6 +2190,23 @@ func (r *bucketIndexReader) reset() {
 // chunk where the series contains the matching label-value pair for a given block of data. Postings can be fetched by
 // single label name=value.
 func (r *bucketIndexReader) ExpandedPostings(ctx context.Context, ms []*labels.Matcher, bytesLimiter BytesLimiter) ([]storage.SeriesRef, error) {
+	// Sort matchers to make sure we generate the same cache key.
+	sort.Slice(ms, func(i, j int) bool {
+		if ms[i].Type == ms[j].Type {
+			if ms[i].Name == ms[j].Name {
+				return ms[i].Value < ms[j].Value
+			}
+			return ms[i].Name < ms[j].Name
+		}
+		return ms[i].Type < ms[j].Type
+	})
+	hit, postings, err := r.fetchExpandedPostingsFromCache(ctx, ms, bytesLimiter)
+	if err != nil {
+		return nil, err
+	}
+	if hit {
+		return postings, nil
+	}
 	var (
 		postingGroups []*postingGroup
 		allRequested  = false
@@ -2280,18 +2302,29 @@ func (r *bucketIndexReader) ExpandedPostings(ctx context.Context, ms []*labels.M
 		return nil, errors.Wrap(err, "expand")
 	}
 
-	// As of version two all series entries are 16 byte padded. All references
-	// we get have to account for that to get the correct offset.
-	version, err := r.block.indexHeaderReader.IndexVersion()
-	if err != nil {
-		return nil, errors.Wrap(err, "get index version")
-	}
-	if version >= 2 {
-		for i, id := range ps {
-			ps[i] = id * 16
+	// Encode postings to cache. We compress and cache postings before adding
+	// 16 bytes padding in order to make compressed size smaller.
+	dataToCache, compressionDuration, compressionErrors, compressedSize := r.encodePostingsToCache(index.NewListPostings(ps), len(ps))
+	r.stats.cachedPostingsCompressions++
+	r.stats.cachedPostingsCompressionErrors += compressionErrors
+	r.stats.CachedPostingsCompressionTimeSum += compressionDuration
+	r.stats.CachedPostingsCompressedSizeSum += units.Base2Bytes(compressedSize)
+	r.stats.CachedPostingsOriginalSizeSum += units.Base2Bytes(len(ps) * 4) // Estimate the posting list size.
+	r.block.indexCache.StoreExpandedPostings(r.block.meta.ULID, ms, dataToCache)
+
+	if len(ps) > 0 {
+		// As of version two all series entries are 16 byte padded. All references
+		// we get have to account for that to get the correct offset.
+		version, err := r.block.indexHeaderReader.IndexVersion()
+		if err != nil {
+			return nil, errors.Wrap(err, "get index version")
+		}
+		if version >= 2 {
+			for i, id := range ps {
+				ps[i] = id * 16
+			}
 		}
 	}
-
 	return ps, nil
 }
 
@@ -2408,6 +2441,51 @@ type postingPtr struct {
 	ptr   index.Range
 }
 
+func (r *bucketIndexReader) fetchExpandedPostingsFromCache(ctx context.Context, ms []*labels.Matcher, bytesLimiter BytesLimiter) (bool, []storage.SeriesRef, error) {
+	dataFromCache, hit := r.block.indexCache.FetchExpandedPostings(ctx, r.block.meta.ULID, ms)
+	if !hit {
+		return false, nil, nil
+	}
+	if err := bytesLimiter.Reserve(uint64(len(dataFromCache))); err != nil {
+		return false, nil, httpgrpc.Errorf(int(codes.ResourceExhausted), "exceeded bytes limit while loading expanded postings from index cache: %s", err)
+	}
+	r.stats.DataDownloadedSizeSum += units.Base2Bytes(len(dataFromCache))
+	r.stats.postingsTouched++
+	r.stats.PostingsTouchedSizeSum += units.Base2Bytes(len(dataFromCache))
+	p, closeFns, err := r.decodeCachedPostings(dataFromCache)
+	defer func() {
+		for _, closeFn := range closeFns {
+			closeFn()
+		}
+	}()
+	// If failed to decode or expand cached postings, return and expand postings again.
+	if err != nil {
+		level.Error(r.block.logger).Log("msg", "failed to decode cached expanded postings, refetch postings", "id", r.block.meta.ULID.String())
+		return false, nil, nil
+	}
+
+	ps, err := index.ExpandPostings(p)
+	if err != nil {
+		level.Error(r.block.logger).Log("msg", "failed to expand cached expanded postings, refetch postings", "id", r.block.meta.ULID.String())
+		return false, nil, nil
+	}
+
+	if len(ps) > 0 {
+		// As of version two all series entries are 16 byte padded. All references
+		// we get have to account for that to get the correct offset.
+		version, err := r.block.indexHeaderReader.IndexVersion()
+		if err != nil {
+			return false, nil, errors.Wrap(err, "get index version")
+		}
+		if version >= 2 {
+			for i, id := range ps {
+				ps[i] = id * 16
+			}
+		}
+	}
+	return true, ps, nil
+}
+
 // fetchPostings fill postings requested by posting groups.
 // It returns one posting for each key, in the same order.
 // If postings for given key is not fetched, entry at given index will be nil.
@@ -2439,32 +2517,12 @@ func (r *bucketIndexReader) fetchPostings(ctx context.Context, keys []labels.Lab
 			r.stats.postingsTouched++
 			r.stats.PostingsTouchedSizeSum += units.Base2Bytes(len(b))
 
-			// Even if this instance is not using compression, there may be compressed
-			// entries in the cache written by other stores.
-			var (
-				l   index.Postings
-				err error
-			)
-			if isDiffVarintSnappyEncodedPostings(b) || isDiffVarintSnappyStreamedEncodedPostings(b) {
-				s := time.Now()
-				clPostings, err := decodePostings(b)
-				r.stats.cachedPostingsDecompressions += 1
-				r.stats.CachedPostingsDecompressionTimeSum += time.Since(s)
-				if err != nil {
-					r.stats.cachedPostingsDecompressionErrors += 1
-				} else {
-					closeFns = append(closeFns, clPostings.close)
-					l = clPostings
-				}
-			} else {
-				_, l, err = r.dec.Postings(b)
-			}
-
+			l, closer, err := r.decodeCachedPostings(b)
 			if err != nil {
 				return nil, closeFns, errors.Wrap(err, "decode postings")
 			}
-
 			output[ix] = l
+			closeFns = append(closeFns, closer...)
 			continue
 		}
 
@@ -2536,27 +2594,12 @@ func (r *bucketIndexReader) fetchPostings(ctx context.Context, keys []labels.Lab
 					return err
 				}
 
-				dataToCache := pBytes
-
-				compressionTime := time.Duration(0)
-				compressions, compressionErrors, compressedSize := 0, 0, 0
-
 				// Reencode postings before storing to cache. If that fails, we store original bytes.
 				// This can only fail, if postings data was somehow corrupted,
 				// and there is nothing we can do about it.
 				// Errors from corrupted postings will be reported when postings are used.
-				compressions++
-				s := time.Now()
 				bep := newBigEndianPostings(pBytes[4:])
-				data, err := diffVarintSnappyStreamedEncode(bep, bep.length())
-				compressionTime = time.Since(s)
-				if err == nil {
-					dataToCache = data
-					compressedSize = len(data)
-				} else {
-					compressionErrors = 1
-				}
-
+				dataToCache, compressionTime, compressionErrors, compressedSize := r.encodePostingsToCache(bep, bep.length())
 				r.mtx.Lock()
 				// Return postings and fill LRU cache.
 				// Truncate first 4 bytes which are length of posting.
@@ -2567,7 +2610,7 @@ func (r *bucketIndexReader) fetchPostings(ctx context.Context, keys []labels.Lab
 				// If we just fetched it we still have to update the stats for touched postings.
 				r.stats.postingsTouched++
 				r.stats.PostingsTouchedSizeSum += units.Base2Bytes(len(pBytes))
-				r.stats.cachedPostingsCompressions += compressions
+				r.stats.cachedPostingsCompressions += 1
 				r.stats.cachedPostingsCompressionErrors += compressionErrors
 				r.stats.CachedPostingsOriginalSizeSum += units.Base2Bytes(len(pBytes))
 				r.stats.CachedPostingsCompressedSizeSum += units.Base2Bytes(compressedSize)
@@ -2581,6 +2624,47 @@ func (r *bucketIndexReader) fetchPostings(ctx context.Context, keys []labels.Lab
 	return output, closeFns, g.Wait()
 }
 
+func (r *bucketIndexReader) decodeCachedPostings(b []byte) (index.Postings, []func(), error) {
+	// Even if this instance is not using compression, there may be compressed
+	// entries in the cache written by other stores.
+	var (
+		l        index.Postings
+		err      error
+		closeFns []func()
+	)
+	if isDiffVarintSnappyEncodedPostings(b) || isDiffVarintSnappyStreamedEncodedPostings(b) {
+		s := time.Now()
+		clPostings, err := decodePostings(b)
+		r.stats.cachedPostingsDecompressions += 1
+		r.stats.CachedPostingsDecompressionTimeSum += time.Since(s)
+		if err != nil {
+			r.stats.cachedPostingsDecompressionErrors += 1
+		} else {
+			closeFns = append(closeFns, clPostings.close)
+			l = clPostings
+		}
+	} else {
+		_, l, err = r.dec.Postings(b)
+	}
+	return l, closeFns, err
+}
+
+func (r *bucketIndexReader) encodePostingsToCache(p index.Postings, length int) ([]byte, time.Duration, int, int) {
+	var dataToCache []byte
+	compressionTime := time.Duration(0)
+	compressionErrors, compressedSize := 0, 0
+	s := time.Now()
+	data, err := diffVarintSnappyStreamedEncode(p, length)
+	compressionTime = time.Since(s)
+	if err == nil {
+		dataToCache = data
+		compressedSize = len(data)
+	} else {
+		compressionErrors = 1
+	}
+	return dataToCache, compressionTime, compressionErrors, compressedSize
+}
+
 func resizePostings(b []byte) ([]byte, error) {
 	d := encoding.Decbuf{B: b}
 	n := d.Be32int()

diff --git a/pkg/store/bucket_e2e_test.go b/pkg/store/bucket_e2e_test.go
@@ -66,6 +66,14 @@ func (c *swappableCache) FetchMultiPostings(ctx context.Context, blockID ulid.UL
 	return c.ptr.FetchMultiPostings(ctx, blockID, keys)
 }
 
+func (c *swappableCache) StoreExpandedPostings(blockID ulid.ULID, matchers []*labels.Matcher, v []byte) {
+	c.ptr.StoreExpandedPostings(blockID, matchers, v)
+}
+
+func (c *swappableCache) FetchExpandedPostings(ctx context.Context, blockID ulid.ULID, matchers []*labels.Matcher) ([]byte, bool) {
+	return c.ptr.FetchExpandedPostings(ctx, blockID, matchers)
+}
+
 func (c *swappableCache) StoreSeries(blockID ulid.ULID, id storage.SeriesRef, v []byte) {
 	c.ptr.StoreSeries(blockID, id, v)
 }

diff --git a/pkg/store/cache/cache.go b/pkg/store/cache/cache.go
@@ -7,6 +7,7 @@ import (
 	"context"
 	"encoding/base64"
 	"strconv"
+	"strings"
 
 	"github.com/oklog/ulid"
 	"github.com/prometheus/prometheus/model/labels"
@@ -15,8 +16,9 @@ import (
 )
 
 const (
-	cacheTypePostings string = "Postings"
-	cacheTypeSeries   string = "Series"
+	cacheTypePostings         string = "Postings"
+	cacheTypeExpandedPostings string = "ExpandedPostings"
+	cacheTypeSeries           string = "Series"
 
 	sliceHeaderSize = 16
 )
@@ -38,6 +40,12 @@ type IndexCache interface {
 	// and returns a map containing cache hits, along with a list of missing keys.
 	FetchMultiPostings(ctx context.Context, blockID ulid.ULID, keys []labels.Label) (hits map[labels.Label][]byte, misses []labels.Label)
 
+	// StoreExpandedPostings stores expanded postings for a set of label matchers.
+	StoreExpandedPostings(blockID ulid.ULID, matchers []*labels.Matcher, v []byte)
+
+	// FetchExpandedPostings fetches expanded postings and returns cached data and a boolean value representing whether it is a cache hit or not.
+	FetchExpandedPostings(ctx context.Context, blockID ulid.ULID, matchers []*labels.Matcher) ([]byte, bool)
+
 	// StoreSeries stores a single series.
 	StoreSeries(blockID ulid.ULID, id storage.SeriesRef, v []byte)
 
@@ -59,6 +67,8 @@ func (c cacheKey) keyType() string {
 		return cacheTypePostings
 	case cacheKeySeries:
 		return cacheTypeSeries
+	case cacheKeyExpandedPostings:
+		return cacheTypeExpandedPostings
 	}
 	return "<unknown>"
 }
@@ -68,6 +78,8 @@ func (c cacheKey) size() uint64 {
 	case cacheKeyPostings:
 		// ULID + 2 slice headers + number of chars in value and name.
 		return ulidSize + 2*sliceHeaderSize + uint64(len(k.Value)+len(k.Name))
+	case cacheKeyExpandedPostings:
+		return ulidSize + sliceHeaderSize + uint64(len(k))
 	case cacheKeySeries:
 		return ulidSize + 8 // ULID + uint64.
 	}
@@ -86,12 +98,34 @@ func (c cacheKey) string() string {
 			key += ":" + c.compression
 		}
 		return key
+	case cacheKeyExpandedPostings:
+		// Use cryptographically hash functions to avoid hash collisions
+		// which would end up in wrong query results.
+		matchers := c.key.(cacheKeyExpandedPostings)
+		matchersHash := blake2b.Sum256([]byte(matchers))
+		key := "EP:" + c.block + ":" + base64.RawURLEncoding.EncodeToString(matchersHash[0:])
+		if len(c.compression) > 0 {
+			key += ":" + c.compression
+		}
+		return key
 	case cacheKeySeries:
 		return "S:" + c.block + ":" + strconv.FormatUint(uint64(c.key.(cacheKeySeries)), 10)
 	default:
 		return ""
 	}
 }
 
+func labelMatchersToString(matchers []*labels.Matcher) string {
+	sb := strings.Builder{}
+	for i, lbl := range matchers {
+		sb.WriteString(lbl.String())
+		if i < len(matchers)-1 {
+			sb.WriteRune(';')
+		}
+	}
+	return sb.String()
+}
+
 type cacheKeyPostings labels.Label
+type cacheKeyExpandedPostings string // We don't use []*labels.Matcher because it is not a hashable type so fail at inmemory cache.
 type cacheKeySeries uint64