WIP

Author: carsonip

x-pack/apm-server/sampling/eventstorage/badger.go

@@ -0,0 +1,129 @@
+package eventstorage
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/dgraph-io/badger/v2"
+
+	"github.com/elastic/apm-data/model/modelpb"
+)
+
+const (
+	// NOTE(axw) these values (and their meanings) must remain stable
+	// over time, to avoid misinterpreting historical data.
+	badgerEntryMetaTraceSampled   = 's'
+	badgerEntryMetaTraceUnsampled = 'u'
+	badgerEntryMetaTraceEvent     = 'e'
+)
+
+type badgerStorage struct {
+	db      *badger.DB
+	codec   Codec
+	enabled bool
+	mu      sync.RWMutex
+}
+
+type BadgerMigrationRW struct {
+	s      *badgerStorage
+	nextRW RW
+}
+
+// WriteTraceSampled records the tail-sampling decision for the given trace ID.
+func (rw *BadgerMigrationRW) WriteTraceSampled(traceID string, sampled bool) error {
+	return rw.nextRW.WriteTraceSampled(traceID, sampled)
+}
+
+// IsTraceSampled reports whether traceID belongs to a trace that is sampled
+// or unsampled. If no sampling decision has been recorded, IsTraceSampled
+// returns ErrNotFound.
+func (rw *BadgerMigrationRW) IsTraceSampled(traceID string) (bool, error) {
+	sampled, err := rw.nextRW.IsTraceSampled(traceID)
+	if err != ErrNotFound {
+		return sampled, err
+	}
+	rw.s.mu.RLock()
+	defer rw.s.mu.RUnlock()
+	if !rw.s.enabled {
+		return sampled, err
+	}
+
+	txn := rw.s.db.NewTransaction(false)
+	defer txn.Discard()
+	item, err := txn.Get([]byte(traceID))
+	if err != nil {
+		if err == badger.ErrKeyNotFound {
+			return false, ErrNotFound
+		}
+		return false, err
+	}
+	return item.UserMeta() == badgerEntryMetaTraceSampled, nil
+}
+
+func (rw *BadgerMigrationRW) WriteTraceEvent(traceID string, id string, event *modelpb.APMEvent) error {
+	return rw.nextRW.WriteTraceEvent(traceID, id, event)
+}
+
+// DeleteTraceEvent deletes the trace event from storage.
+func (rw *BadgerMigrationRW) DeleteTraceEvent(traceID, id string) error {
+	// FIXME: inclined to not delete from badger.
+	// At worst it will produce duplicates if apm-server restarts without persisting pubsub checkpoint.
+	return rw.nextRW.DeleteTraceEvent(traceID, id)
+}
+
+// ReadTraceEvents reads trace events with the given trace ID from storage into out.
+func (rw *BadgerMigrationRW) ReadTraceEvents(traceID string, out *modelpb.Batch) error {
+	err := rw.nextRW.ReadTraceEvents(traceID, out)
+
+	rw.s.mu.RLock()
+	defer rw.s.mu.RUnlock()
+	if !rw.s.enabled {
+		return err
+	}
+
+	txn := rw.s.db.NewTransaction(false)
+	opts := badger.DefaultIteratorOptions
+	opts.Prefix = append([]byte(traceID), ':')
+
+	// 1st pass: check whether there exist keys matching the prefix.
+	// Do not prefetch values so that the check is done in-memory.
+	// This is to optimize for cases when it is a miss.
+	opts.PrefetchValues = false
+	iter := txn.NewIterator(opts)
+	iter.Rewind()
+	if !iter.Valid() {
+		iter.Close()
+		return nil
+	}
+	iter.Close()
+
+	// 2nd pass: this is only done when there exist keys matching the prefix.
+	// Fetch the events with PrefetchValues for performance.
+	// This is to optimize for cases when it is a hit.
+	opts.PrefetchValues = true
+	iter = txn.NewIterator(opts)
+	defer iter.Close()
+	for iter.Rewind(); iter.Valid(); iter.Next() {
+		item := iter.Item()
+		if item.IsDeletedOrExpired() {
+			continue
+		}
+		switch item.UserMeta() {
+		case badgerEntryMetaTraceEvent:
+			event := &modelpb.APMEvent{}
+			if err := item.Value(func(data []byte) error {
+				if err := rw.s.codec.DecodeEvent(data, event); err != nil {
+					return fmt.Errorf("codec failed to decode event: %w", err)
+				}
+				return nil
+			}); err != nil {
+				return err
+			}
+			*out = append(*out, event)
+		default:
+			// Unknown entry meta: ignore.
+			continue
+		}
+	}
+	return nil
+}