Add common class and interface needed for tracking average field length for index fields.

2 files changed, 54 insertions, 0 deletions

diff --git a/searchlib/src/vespa/searchlib/index/field_length_info.h b/searchlib/src/vespa/searchlib/index/field_length_info.h
new file mode 100644
index 00000000000..3ae3d38d86e
--- /dev/null
+++ b/searchlib/src/vespa/searchlib/index/field_length_info.h
@@ -0,0 +1,31 @@
+// Copyright 2019 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+namespace search::index {
+
+/**
+ * Information about average field length for a single index field.
+ */
+class FieldLengthInfo {
+private:
+    double   _average_field_length;
+    uint32_t _num_samples;
+
+public:
+    FieldLengthInfo()
+        : FieldLengthInfo(0.0, 0)
+    {
+    }
+
+    FieldLengthInfo(double average_field_length, uint32_t num_samples)
+        : _average_field_length(average_field_length),
+          _num_samples(num_samples)
+    {
+    }
+
+    double get_average_field_length() const { return _average_field_length; }
+    uint32_t get_num_samples() const { return _num_samples; }
+};
+
+}
diff --git a/searchlib/src/vespa/searchlib/index/i_field_length_inspector.h b/searchlib/src/vespa/searchlib/index/i_field_length_inspector.h
new file mode 100644
index 00000000000..31b0a44b0c3
--- /dev/null
+++ b/searchlib/src/vespa/searchlib/index/i_field_length_inspector.h
@@ -0,0 +1,23 @@
+// Copyright 2019 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include "field_length_info.h"
+#include <vespa/vespalib/stllike/string.h>
+
+namespace search::index {
+
+/**
+ * Interface used to inspect field length info for various index fields.
+ */
+class IFieldLengthInspector {
+public:
+    virtual ~IFieldLengthInspector() {}
+
+    /**
+     * Returns the field length info for the given index field, or empty info if the field is not found.
+     */
+    virtual FieldLengthInfo get_field_length_info(const vespalib::string& field_name) const = 0;
+};
+
+}