1 files changed, 54 insertions, 0 deletions
diff --git a/vendor/github.com/blevesearch/zap/v13/chunk.go b/vendor/github.com/blevesearch/zap/v13/chunk.go
new file mode 100644
index 0000000000..fe9f398da6
--- /dev/null
+++ b/vendor/github.com/blevesearch/zap/v13/chunk.go
@@ -0,0 +1,54 @@
+//  Copyright (c) 2019 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//              http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package zap
+
+import (
+	"fmt"
+)
+
+// LegacyChunkMode was the original chunk mode (always chunk size 1024)
+// this mode is still used for chunking doc values.
+var LegacyChunkMode uint32 = 1024
+
+// DefaultChunkMode is the most recent improvement to chunking and should
+// be used by default.
+var DefaultChunkMode uint32 = 1025
+
+func getChunkSize(chunkMode uint32, cardinality uint64, maxDocs uint64) (uint64, error) {
+	switch {
+	// any chunkMode <= 1024 will always chunk with chunkSize=chunkMode
+	case chunkMode <= 1024:
+		// legacy chunk size
+		return uint64(chunkMode), nil
+
+	case chunkMode == 1025:
+		// attempt at simple improvement
+		// theory - the point of chunking is to put a bound on the maximum number of
+		// calls to Next() needed to find a random document.  ie, you should be able
+		// to do one jump to the correct chunk, and then walk through at most
+		// chunk-size items
+		// previously 1024 was chosen as the chunk size, but this is particularly
+		// wasteful for low cardinality terms.  the observation is that if there
+		// are less than 1024 items, why not put them all in one chunk,
+		// this way you'll still achieve the same goal of visiting at most
+		// chunk-size items.
+		// no attempt is made to tweak any other case
+		if cardinality <= 1024 {
+			return maxDocs, nil
+		}
+		return 1024, nil
+	}
+	return 0, fmt.Errorf("unknown chunk mode %d", chunkMode)
+}