Add support for specifying max number of samples in field length calculator

constructor.

2 files changed, 11 insertions, 10 deletions

diff --git a/searchlib/src/tests/index/field_length_calculator/field_length_calculator_test.cpp b/searchlib/src/tests/index/field_length_calculator/field_length_calculator_test.cpp
index f61a7f103fa..c99d241cbc0 100644
--- a/searchlib/src/tests/index/field_length_calculator/field_length_calculator_test.cpp
+++ b/searchlib/src/tests/index/field_length_calculator/field_length_calculator_test.cpp
@@ -36,15 +36,15 @@ TEST(FieldLengthCalculatorTest, startup_is_average)
     EXPECT_DOUBLE_EQ((3 + 4 + 7)/3.0, calc.get_average_field_length());
     EXPECT_EQ(3, calc.get_num_samples());
     calc.add_field_length(9);
-    EXPECT_DOUBLE_EQ(5.75, calc.get_average_field_length());
+    EXPECT_DOUBLE_EQ((3 + 4 + 7 + 9)/4.0, calc.get_average_field_length());
     EXPECT_EQ(4, calc.get_num_samples());
 }
 
 TEST(FieldLengthCalculatorTest, average_until_max_num_samples)
 {
-    FieldLengthCalculator calc;
+    const uint32_t max_num_samples = 5;
+    FieldLengthCalculator calc(0.0, 0, max_num_samples);
     static constexpr double epsilon = 0.000000001; // Allowed difference
-    const uint32_t max_num_samples = calc.get_max_num_samples();
     for (uint32_t i = 0; i + 1 < max_num_samples; ++i) {
         calc.add_field_length(i + 1);
     }
@@ -59,7 +59,7 @@ TEST(FieldLengthCalculatorTest, average_until_max_num_samples)
     // No longer arithmetic average
     EXPECT_LT(arith_avg(max_num_samples + 1), calc.get_average_field_length());
     // Switched to exponential decay
-    EXPECT_NEAR((arith_avg(max_num_samples) * (max_num_samples - 1) + max_num_samples + 1) / max_num_samples, calc.get_average_field_length(), 0.000000001);
+    EXPECT_NEAR((arith_avg(max_num_samples) * (max_num_samples - 1) + max_num_samples + 1) / max_num_samples, calc.get_average_field_length(), epsilon);
     EXPECT_EQ(max_num_samples, calc.get_num_samples());
 }
 
diff --git a/searchlib/src/vespa/searchlib/index/field_length_calculator.h b/searchlib/src/vespa/searchlib/index/field_length_calculator.h
index e3323654e20..50d47ced063 100644
--- a/searchlib/src/vespa/searchlib/index/field_length_calculator.h
+++ b/searchlib/src/vespa/searchlib/index/field_length_calculator.h
@@ -7,12 +7,12 @@ namespace search::index {
 
 /**
  * Class used to calculate average field length, with a bias towards
- * the latest field lengths when MAX_NUM_SAMPLES samples have been reached.
+ * the latest field lengths when max_num_samples samples have been reached.
  */
 class FieldLengthCalculator {
     std::atomic<double>   _average_field_length;
     uint32_t              _num_samples;     // Capped by _max_num_samples
-    static constexpr uint32_t    MAX_NUM_SAMPLES = 100000;
+    uint32_t              _max_num_samples;
 
 public:
     FieldLengthCalculator()
@@ -20,18 +20,19 @@ public:
     {
     }
 
-    FieldLengthCalculator(double average_field_length, uint32_t num_samples)
+    FieldLengthCalculator(double average_field_length, uint32_t num_samples, uint32_t max_num_samples = 100000)
         : _average_field_length(average_field_length),
-          _num_samples(std::min(num_samples, MAX_NUM_SAMPLES))
+          _num_samples(std::min(num_samples, max_num_samples)),
+          _max_num_samples(max_num_samples)
     {
     }
 
     double get_average_field_length() const { return _average_field_length.load(std::memory_order_relaxed); }
     uint32_t get_num_samples() const { return _num_samples; }
-    static constexpr uint32_t get_max_num_samples() { return MAX_NUM_SAMPLES; }
+    uint32_t get_max_num_samples() { return _max_num_samples; }
     
     void add_field_length(uint32_t field_length) {
-        if (_num_samples < MAX_NUM_SAMPLES) {
+        if (_num_samples < _max_num_samples) {
             ++_num_samples;
         }
         _average_field_length.store((_average_field_length.load(std::memory_order_relaxed) * (_num_samples - 1) + field_length) / _num_samples, std::memory_order_relaxed);