feat: compute tbs entry size before writing and flush to avoid limit error

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

@@ -20,6 +20,8 @@ const (
 	entryMetaTraceSampled   = 's'
 	entryMetaTraceUnsampled = 'u'
 	entryMetaTraceEvent     = 'e'
+
+	defaultPendingSize = 1024
 )
 
 var (
@@ -65,8 +67,9 @@ func (s *Storage) NewShardedReadWriter() *ShardedReadWriter {
 // The returned ReadWriter must be closed when it is no longer needed.
 func (s *Storage) NewReadWriter() *ReadWriter {
 	return &ReadWriter{
-		s:   s,
-		txn: s.db.NewTransaction(true),
+		s:           s,
+		txn:         s.db.NewTransaction(true),
+		pendingSize: defaultPendingSize,
 	}
 }
 
@@ -105,6 +108,7 @@ type ReadWriter struct {
 	// be unmodified until the end of a transaction.
 	readKeyBuf    []byte
 	pendingWrites int
+	pendingSize   int64
 }
 
 // Close closes the writer. Any writes that have not been flushed may be lost.
@@ -126,19 +130,10 @@ func (rw *ReadWriter) Close() {
 // files exceeds the configured threshold.
 func (rw *ReadWriter) Flush(limit int64) error {
 	const flushErrFmt = "failed to flush pending writes: %w"
-	if current, limitReached := rw.s.limitReached(limit); limitReached {
-		// Discard the txn and re-create it if the soft limit has been reached.
-		rw.txn.Discard()
-		rw.txn = rw.s.db.NewTransaction(true)
-		rw.pendingWrites = 0
-		return fmt.Errorf(
-			flushErrFmt+" (current: %d, limit: %d)",
-			ErrLimitReached, current, limit,
-		)
-	}
 	err := rw.txn.Commit()
 	rw.txn = rw.s.db.NewTransaction(true)
 	rw.pendingWrites = 0
+	rw.pendingSize = defaultPendingSize
 	if err != nil {
 		return fmt.Errorf(flushErrFmt, err)
 	}
@@ -185,18 +180,26 @@ func (rw *ReadWriter) WriteTraceEvent(traceID string, id string, event *modelpb.
 
 func (rw *ReadWriter) writeEntry(e *badger.Entry, opts WriterOpts) error {
 	rw.pendingWrites++
-	err := rw.txn.SetEntry(e.WithTTL(opts.TTL))
-	// Attempt to flush if there are 200 or more uncommitted writes.
-	// This ensures calls to ReadTraceEvents are not slowed down;
-	// ReadTraceEvents uses an iterator, which must sort all keys
-	// of uncommitted writes.
-	// The 200 value yielded a good balance between read and write speed:
-	// https://github.com/elastic/apm-server/pull/8407#issuecomment-1162994643
-	if rw.pendingWrites >= 200 {
+	entrySize := int64(estimateSize(e)) + 10
+	lsm, vlog := rw.s.db.Size()
+
+	if rw.pendingSize+entrySize+lsm+vlog >= opts.StorageLimitInBytes {
+		if err := rw.Flush(opts.StorageLimitInBytes); err != nil {
+			return err
+		}
+	} else if rw.pendingWrites >= 200 {
+		// Attempt to flush if there are 200 or more uncommitted writes.
+		// This ensures calls to ReadTraceEvents are not slowed down;
+		// ReadTraceEvents uses an iterator, which must sort all keys
+		// of uncommitted writes.
+		// The 200 value yielded a good balance between read and write speed:
+		// https://github.com/elastic/apm-server/pull/8407#issuecomment-1162994643
 		if err := rw.Flush(opts.StorageLimitInBytes); err != nil {
 			return err
 		}
 	}
+	err := rw.txn.SetEntry(e.WithTTL(opts.TTL))
+
 	// If the transaction is already too big to accommodate the new entry, flush
 	// the existing transaction and set the entry on a new one, otherwise,
 	// returns early.
@@ -206,9 +209,14 @@ func (rw *ReadWriter) writeEntry(e *badger.Entry, opts WriterOpts) error {
 	if err := rw.Flush(opts.StorageLimitInBytes); err != nil {
 		return err
 	}
+	rw.pendingSize += entrySize
 	return rw.txn.SetEntry(e)
 }
 
+func estimateSize(e *badger.Entry) int {
+	return len(e.Key) + len(e.Value) + 12 + 2
+}
+
 // DeleteTraceEvent deletes the trace event from storage.
 func (rw *ReadWriter) DeleteTraceEvent(traceID, id string) error {
 	key := append(append([]byte(traceID), ':'), id...)