Fix QueryStatistics.ExecutionAvgTime calculation (#2968)

Author: maikschott

src/NHibernate.Test/Async/Stats/StatsFixture.cs

@@ -214,6 +214,14 @@ public async Task QueryStatGatheringAsync()
 			maxTime = sqlStats.ExecutionMaxTime;
 			Assert.AreEqual(maxTime, stats.QueryExecutionMaxTime);
 			Assert.AreEqual( sql, stats.QueryExecutionMaxTimeQueryString);
+
+			// check that 2nd query correctly updates query statistics
+			results = (await (s.CreateSQLQuery(sql).AddEntity(typeof(Country)).ListAsync())).Count;
+			var queryTime1 = maxTime;
+			var queryTime2 = sqlStats.ExecutionMaxTime == maxTime ? sqlStats.ExecutionMinTime : sqlStats.ExecutionMaxTime;
+			Assert.AreEqual(2, sqlStats.ExecutionCount, "unexpected execution count");
+			Assert.AreEqual((queryTime1 + queryTime2).Ticks / 2, sqlStats.ExecutionAvgTime.Ticks, 2, "unexpected average time");
+
 			await (tx.CommitAsync());
 			s.Close();
 

src/NHibernate.Test/Stats/StatsFixture.cs

@@ -202,6 +202,14 @@ public void QueryStatGathering()
 			maxTime = sqlStats.ExecutionMaxTime;
 			Assert.AreEqual(maxTime, stats.QueryExecutionMaxTime);
 			Assert.AreEqual( sql, stats.QueryExecutionMaxTimeQueryString);
+
+			// check that 2nd query correctly updates query statistics
+			results = s.CreateSQLQuery(sql).AddEntity(typeof(Country)).List().Count;
+			var queryTime1 = maxTime;
+			var queryTime2 = sqlStats.ExecutionMaxTime == maxTime ? sqlStats.ExecutionMinTime : sqlStats.ExecutionMaxTime;
+			Assert.AreEqual(2, sqlStats.ExecutionCount, "unexpected execution count");
+			Assert.AreEqual((queryTime1 + queryTime2).Ticks / 2, sqlStats.ExecutionAvgTime.Ticks, 2, "unexpected average time");
+
 			tx.Commit();
 			s.Close();
 

src/NHibernate/Stat/QueryStatistics.cs

@@ -70,7 +70,7 @@ internal void Executed(long rows, TimeSpan time)
 				executionMaxTime = time;
 			executionCount++;
 			executionRowCount += rows;
-			executionAvgTime = TimeSpan.FromTicks((executionAvgTime.Ticks * executionCount + time.Ticks) / executionCount);
+			executionAvgTime = TimeSpan.FromTicks((executionAvgTime.Ticks * (executionCount - 1) + time.Ticks) / executionCount);
 		}
 
 		public override string ToString()