Fix retried docs to not be in FailedDocs (#170)

A document should either be retried or failed in a request.

appender.go

@@ -366,7 +366,13 @@ func (a *Appender) flush(ctx context.Context, bulkIndexer *BulkIndexer) error {
 		}
 		return err
 	}
-	var docsFailed, docsIndexed, tooManyRequests, clientFailed, serverFailed int64
+	var (
+		docsFailed, docsIndexed,
+		// breakdown of failed docs:
+		tooManyRequests, // failed after document retries (if it applies) and final status is 429
+		clientFailed, // failed after document retries (if it applies) and final status is 400s excluding 429
+		serverFailed int64 // failed after document retries (if it applies) and final status is 500s
+	)
 	docsIndexed = resp.Indexed
 	var failedCount map[BulkIndexerResponseItem]int
 	if len(resp.FailedDocs) > 0 {
@@ -401,6 +407,7 @@ func (a *Appender) flush(ctx context.Context, bulkIndexer *BulkIndexer) error {
 		atomic.AddInt64(&a.docsFailed, docsFailed)
 	}
 	if resp.RetriedDocs > 0 {
+		// docs are scheduled to be retried but not yet failed due to retry limit
 		a.addCount(resp.RetriedDocs,
 			nil,
 			a.metrics.docsRetried,

bulk_indexer.go

@@ -491,9 +491,10 @@ func (b *BulkIndexer) Flush(ctx context.Context) (BulkIndexerResponseStat, error
 			}
 		}
 
-		if len(tmp) > 0 {
-			resp.FailedDocs = tmp
-		}
+		// FailedDocs contain responses of
+		// - non-retriable errors
+		// - retriable errors that reached the retry limit
+		resp.FailedDocs = tmp
 	}
 
 	return resp, nil

bulk_indexer_test.go

@@ -102,7 +102,7 @@ func TestBulkIndexer(t *testing.T) {
 				stat, err := indexer.Flush(context.Background())
 				require.NoError(t, err)
 				require.Equal(t, int64(0), stat.Indexed)
-				require.Equal(t, itemCount, len(stat.FailedDocs))
+				require.Len(t, stat.FailedDocs, 0)
 				require.Equal(t, int64(itemCount), stat.RetriedDocs)
 
 				// all the flushed bytes are now in the buffer again to be retried