diff --git a/src/DotNetCore.CAP.MySql/IDataStorage.MySql.cs b/src/DotNetCore.CAP.MySql/IDataStorage.MySql.cs
index f4eb5b3..4db2b94 100644
--- a/src/DotNetCore.CAP.MySql/IDataStorage.MySql.cs
+++ b/src/DotNetCore.CAP.MySql/IDataStorage.MySql.cs
@@ -191,26 +191,23 @@ namespace DotNetCore.CAP.MySql
 
         private async Task<IEnumerable<MediumMessage>> GetMessagesOfNeedRetryAsync(string sql)
         {
-            List<MediumMessage> result;
-            await using (var connection = new MySqlConnection(_options.Value.ConnectionString))
+            await using var connection = new MySqlConnection(_options.Value.ConnectionString);
+            var result = connection.ExecuteReader(sql, reader =>
             {
-                result = connection.ExecuteReader(sql, reader =>
+                var messages = new List<MediumMessage>();
+                while (reader.Read())
                 {
-                    var messages = new List<MediumMessage>();
-                    while (reader.Read())
+                    messages.Add(new MediumMessage
                     {
-                        messages.Add(new MediumMessage
-                        {
-                            DbId = reader.GetInt64(0).ToString(),
-                            Origin = StringSerializer.DeSerialize(reader.GetString(1)),
-                            Retries = reader.GetInt32(2),
-                            Added = reader.GetDateTime(3)
-                        });
-                    }
-
-                    return messages;
-                });
-            }
+                        DbId = reader.GetInt64(0).ToString(),
+                        Origin = StringSerializer.DeSerialize(reader.GetString(1)),
+                        Retries = reader.GetInt32(2),
+                        Added = reader.GetDateTime(3)
+                    });
+                }
+
+                return messages;
+            });
 
             return result;
         }
diff --git a/src/DotNetCore.CAP.MySql/IMonitoringApi.MySql.cs b/src/DotNetCore.CAP.MySql/IMonitoringApi.MySql.cs
index bd50445..31d6189 100644
--- a/src/DotNetCore.CAP.MySql/IMonitoringApi.MySql.cs
+++ b/src/DotNetCore.CAP.MySql/IMonitoringApi.MySql.cs
@@ -30,39 +30,35 @@ namespace DotNetCore.CAP.MySql
         public StatisticsDto GetStatistics()
         {
             var sql = $@"
-    set transaction isolation level read committed;
-    SELECT
-    (
-        SELECT COUNT(Id) FROM `{_pubName}` WHERE StatusName = N'Succeeded'
-    ) AS PublishedSucceeded,
-    (
-        SELECT COUNT(Id) FROM `{_recName}` WHERE StatusName = N'Succeeded'
-    ) AS ReceivedSucceeded,
-    (
-        SELECT COUNT(Id) FROM `{_pubName}` WHERE StatusName = N'Failed'
-    ) AS PublishedFailed,
-    (
-        SELECT COUNT(Id) FROM `{_recName}` WHERE StatusName = N'Failed'
-    ) AS ReceivedFailed;";
-
-            StatisticsDto statistics;
-            using (var connection = new MySqlConnection(_options.ConnectionString))
+SELECT
+(
+    SELECT COUNT(Id) FROM `{_pubName}` WHERE StatusName = N'Succeeded'
+) AS PublishedSucceeded,
+(
+    SELECT COUNT(Id) FROM `{_recName}` WHERE StatusName = N'Succeeded'
+) AS ReceivedSucceeded,
+(
+    SELECT COUNT(Id) FROM `{_pubName}` WHERE StatusName = N'Failed'
+) AS PublishedFailed,
+(
+    SELECT COUNT(Id) FROM `{_recName}` WHERE StatusName = N'Failed'
+) AS ReceivedFailed;";
+
+            using var connection = new MySqlConnection(_options.ConnectionString);
+            var statistics = connection.ExecuteReader(sql, reader =>
             {
-                statistics = connection.ExecuteReader(sql, reader =>
-                {
-                    var statisticsDto = new StatisticsDto();
+                var statisticsDto = new StatisticsDto();
 
-                    while (reader.Read())
-                    {
-                        statisticsDto.PublishedSucceeded = reader.GetInt32(0);
-                        statisticsDto.ReceivedSucceeded = reader.GetInt32(1);
-                        statisticsDto.PublishedFailed = reader.GetInt32(2);
-                        statisticsDto.ReceivedFailed = reader.GetInt32(3);
-                    }
+                while (reader.Read())
+                {
+                    statisticsDto.PublishedSucceeded = reader.GetInt32(0);
+                    statisticsDto.ReceivedSucceeded = reader.GetInt32(1);
+                    statisticsDto.PublishedFailed = reader.GetInt32(2);
+                    statisticsDto.ReceivedFailed = reader.GetInt32(3);
+                }
 
-                    return statisticsDto;
-                });
-            }
+                return statisticsDto;
+            });
 
             return statistics;
         }
@@ -189,15 +185,17 @@ namespace DotNetCore.CAP.MySql
             string statusName,
             IDictionary<string, DateTime> keyMaps)
         {
-            var sqlQuery =
-                $@"
-select aggr.* from (
-    select date_format(`Added`,'%Y-%m-%d-%H') as `Key`,
-        count(id) `Count`
-    from  `{tableName}`
-    where StatusName = @statusName
-    group by date_format(`Added`,'%Y-%m-%d-%H')
-) aggr where `Key` >= @minKey and `Key` <= @maxKey;";
+            var sqlQuery = $@"
+SELECT aggr.*
+FROM (
+         SELECT date_format(`Added`, '%Y-%m-%d-%H') AS `Key`,
+                count(id)                              `Count`
+         FROM `{tableName}`
+         WHERE StatusName = @statusName
+         GROUP BY date_format(`Added`, '%Y-%m-%d-%H')
+     ) aggr
+WHERE `Key` >= @minKey
+  AND `Key` <= @maxKey;";
 
             object[] sqlParams =
             {
@@ -249,7 +247,7 @@ select aggr.* from (
             var sql = $@"SELECT `Id` as DbId, `Content`,`Added`,`ExpiresAt`,`Retries` FROM `{tableName}` WHERE Id={id};";
 
             await using var connection = new MySqlConnection(_options.ConnectionString);
-            var mediumMessae = connection.ExecuteReader(sql, reader =>
+            var mediumMessage = connection.ExecuteReader(sql, reader =>
             {
                 MediumMessage message = null;
 
@@ -268,13 +266,7 @@ select aggr.* from (
                 return message;
             });
 
-            return mediumMessae;
+            return mediumMessage;
         }
     }
-
-    class TimelineCounter
-    {
-        public string Key { get; set; }
-        public int Count { get; set; }
-    }
 }
\ No newline at end of file
diff --git a/src/DotNetCore.CAP.PostgreSql/IDataStorage.PostgreSql.cs b/src/DotNetCore.CAP.PostgreSql/IDataStorage.PostgreSql.cs
index 3c06288..1cf0ce7 100644
--- a/src/DotNetCore.CAP.PostgreSql/IDataStorage.PostgreSql.cs
+++ b/src/DotNetCore.CAP.PostgreSql/IDataStorage.PostgreSql.cs
@@ -135,7 +135,7 @@ namespace DotNetCore.CAP.PostgreSql
         public async Task<int> DeleteExpiresAsync(string table, DateTime timeout, int batchCount = 1000,
             CancellationToken token = default)
         {
-            using var connection = new NpgsqlConnection(_options.Value.ConnectionString);
+            await using var connection = new NpgsqlConnection(_options.Value.ConnectionString);
             var count = connection.ExecuteNonQuery(
                 $"DELETE FROM {table} WHERE \"ExpiresAt\" < @timeout AND \"Id\" IN (SELECT \"Id\" FROM {table} LIMIT @batchCount);", null,
                 new NpgsqlParameter("@timeout", timeout), new NpgsqlParameter("@batchCount", batchCount));
@@ -179,7 +179,7 @@ namespace DotNetCore.CAP.PostgreSql
                 new NpgsqlParameter("@StatusName", state.ToString("G"))
             };
 
-            using var connection = new NpgsqlConnection(_options.Value.ConnectionString);
+            await using var connection = new NpgsqlConnection(_options.Value.ConnectionString);
             connection.ExecuteNonQuery(sql, sqlParams: sqlParams);
 
             await Task.CompletedTask;
@@ -197,28 +197,25 @@ namespace DotNetCore.CAP.PostgreSql
 
         private async Task<IEnumerable<MediumMessage>> GetMessagesOfNeedRetryAsync(string sql)
         {
-            List<MediumMessage> result;
-            using (var connection = new NpgsqlConnection(_options.Value.ConnectionString))
+            await using var connection = new NpgsqlConnection(_options.Value.ConnectionString);
+            var result = connection.ExecuteReader(sql, reader =>
             {
-                result = connection.ExecuteReader(sql, reader =>
+                var messages = new List<MediumMessage>();
+                while (reader.Read())
                 {
-                    var messages = new List<MediumMessage>();
-                    while (reader.Read())
+                    messages.Add(new MediumMessage
                     {
-                        messages.Add(new MediumMessage
-                        {
-                            DbId = reader.GetInt64(0).ToString(),
-                            Origin = StringSerializer.DeSerialize(reader.GetString(1)),
-                            Retries = reader.GetInt32(2),
-                            Added = reader.GetDateTime(3)
-                        });
-                    }
-
-                    return messages;
-                });
-            }
+                        DbId = reader.GetInt64(0).ToString(),
+                        Origin = StringSerializer.DeSerialize(reader.GetString(1)),
+                        Retries = reader.GetInt32(2),
+                        Added = reader.GetDateTime(3)
+                    });
+                }
+
+                return messages;
+            });
 
-            return await Task.FromResult(result);
+            return result;
         }
     }
 }
\ No newline at end of file
diff --git a/src/DotNetCore.CAP.PostgreSql/IMonitoringApi.PostgreSql.cs b/src/DotNetCore.CAP.PostgreSql/IMonitoringApi.PostgreSql.cs
index 8f6722f..9cae360 100644
--- a/src/DotNetCore.CAP.PostgreSql/IMonitoringApi.PostgreSql.cs
+++ b/src/DotNetCore.CAP.PostgreSql/IMonitoringApi.PostgreSql.cs
@@ -238,8 +238,8 @@ select ""Key"",""Count"" from aggr where ""Key"" >= @minKey and ""Key"" <= @maxK
         {
             var sql = $@"SELECT ""Id"" AS ""DbId"", ""Content"", ""Added"", ""ExpiresAt"", ""Retries"" FROM {tableName} WHERE ""Id""={id} FOR UPDATE SKIP LOCKED";
 
-            using var connection = new NpgsqlConnection(_options.ConnectionString);
-            var mediumMessae = connection.ExecuteReader(sql, reader =>
+            await using var connection = new NpgsqlConnection(_options.ConnectionString);
+            var mediumMessage = connection.ExecuteReader(sql, reader =>
             {
                 MediumMessage message = null;
 
@@ -258,13 +258,7 @@ select ""Key"",""Count"" from aggr where ""Key"" >= @minKey and ""Key"" <= @maxK
                 return message;
             });
 
-            return await Task.FromResult(mediumMessae);
+            return await Task.FromResult(mediumMessage);
         }
-    }
-
-    internal class TimelineCounter
-    {
-        public string Key { get; set; }
-        public int Count { get; set; }
-    }
+    } 
 }
\ No newline at end of file
diff --git a/src/DotNetCore.CAP.SqlServer/IMonitoringApi.SqlServer.cs b/src/DotNetCore.CAP.SqlServer/IMonitoringApi.SqlServer.cs
index ddf6ef2..3e908d5 100644
--- a/src/DotNetCore.CAP.SqlServer/IMonitoringApi.SqlServer.cs
+++ b/src/DotNetCore.CAP.SqlServer/IMonitoringApi.SqlServer.cs
@@ -30,39 +30,35 @@ namespace DotNetCore.CAP.SqlServer
         public StatisticsDto GetStatistics()
         {
             var sql = $@"
-    SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
-    SELECT
-    (
-        SELECT COUNT(Id) FROM {_pubName} WHERE StatusName = N'Succeeded'
-    ) AS PublishedSucceeded,
-    (
-        SELECT COUNT(Id) FROM {_recName} WHERE StatusName = N'Succeeded'
-    ) AS ReceivedSucceeded,
-    (
-        SELECT COUNT(Id) FROM {_pubName} WHERE StatusName = N'Failed'
-    ) AS PublishedFailed,
-    (
-        SELECT COUNT(Id) FROM {_recName} WHERE StatusName = N'Failed'
-    ) AS ReceivedFailed;";
-
-            StatisticsDto statistics;
-            using (var connection = new SqlConnection(_options.ConnectionString))
+SELECT
+(
+    SELECT COUNT(Id) FROM {_pubName} WHERE StatusName = N'Succeeded'
+) AS PublishedSucceeded,
+(
+    SELECT COUNT(Id) FROM {_recName} WHERE StatusName = N'Succeeded'
+) AS ReceivedSucceeded,
+(
+    SELECT COUNT(Id) FROM {_pubName} WHERE StatusName = N'Failed'
+) AS PublishedFailed,
+(
+    SELECT COUNT(Id) FROM {_recName} WHERE StatusName = N'Failed'
+) AS ReceivedFailed;";
+
+            using var connection = new SqlConnection(_options.ConnectionString);
+            var statistics = connection.ExecuteReader(sql, reader =>
             {
-                statistics = connection.ExecuteReader(sql, reader =>
-                {
-                    var statisticsDto = new StatisticsDto();
+                var statisticsDto = new StatisticsDto();
 
-                    while (reader.Read())
-                    {
-                        statisticsDto.PublishedSucceeded = reader.GetInt32(0);
-                        statisticsDto.ReceivedSucceeded = reader.GetInt32(1);
-                        statisticsDto.PublishedFailed = reader.GetInt32(2);
-                        statisticsDto.ReceivedFailed = reader.GetInt32(3);
-                    }
+                while (reader.Read())
+                {
+                    statisticsDto.PublishedSucceeded = reader.GetInt32(0);
+                    statisticsDto.ReceivedSucceeded = reader.GetInt32(1);
+                    statisticsDto.PublishedFailed = reader.GetInt32(2);
+                    statisticsDto.ReceivedFailed = reader.GetInt32(3);
+                }
 
-                    return statisticsDto;
-                });
-            }
+                return statisticsDto;
+            });
 
             return statistics;
         }
@@ -253,7 +249,7 @@ select [Key], [Count] from aggr with (nolock) where [Key] >= @minKey and [Key] <
             var sql = $@"SELECT TOP 1 Id AS DbId, Content, Added, ExpiresAt, Retries FROM {tableName} WITH (readpast) WHERE Id={id}";
 
             using var connection = new SqlConnection(_options.ConnectionString);
-            var mediumMessae = connection.ExecuteReader(sql, reader =>
+            var mediumMessage = connection.ExecuteReader(sql, reader =>
             {
                 MediumMessage message = null;
 
@@ -272,13 +268,7 @@ select [Key], [Count] from aggr with (nolock) where [Key] >= @minKey and [Key] <
                 return message;
             });
 
-            return await Task.FromResult(mediumMessae);
+            return await Task.FromResult(mediumMessage);
         }
-    }
-
-    internal class TimelineCounter
-    {
-        public string Key { get; set; }
-        public int Count { get; set; }
-    }
+    } 
 }
\ No newline at end of file