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更新时间：2024-09-11 GMT+08:00
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大事务检测能力

众所周知，大事务的存在对实例的健康平稳运行有一些影响，典型场景如大事务的回滚时间很长，会导致升级、规格变更时间变长。GaussDB(for MySQL)提供了大事务检测的能力，当出现大事务，可以通过告警通知客户及时提交。

前提条件

  • 内核2.0.39.230300及以上版本支持该功能。
  • 需要根据以下条件设置对应的参数值为“ON”。
    • 内核版本小于2.0.45.230900时，需要确认“log-bin”参数值为“ON”。
    • 内核版本大于或等于2.0.45.230900时，需要确认“rds_global_sql_log_bin”参数值为“ON”。

使用方法

  1. 增加系统变量“rds_warn_max_binlog_cache_size”检测大事务。
    表1 参数说明

    参数名称

    级别

    描述

    rds_warn_max_binlog_cache_size

    global

    当大事务产生的Binlog超过该值时，则报WARNING提示客户。

    默认值为：18446744073709547520

    取值范围为：[4096，18446744073709547520]

    事务产生的Binlog大小超过rds_warn_max_binlog_cache_size时，为了提醒客户及时提交事务，系统会报WARNING到客户端。为了避免给客户端发送多个WARNING，限制事务中每个statement发送一次这个WARNING给客户端。

    当配置rds_warn_max_binlog_cache_size为40KB(40960)：

    mysql> CREATE TABLE t1 (
    -> a longtext
    -> ) DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.12 sec)

mysql> show variables like 'rds_warn_max_binlog_cache_size';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| rds_warn_max_binlog_cache_size | 40960 |
+--------------------------------+-------+
1 row in set (0.01 sec)

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                             |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 4008 | Recommend you to INSERT/UPDATE/DELETE rows in batches by multiple transactions. The current transaction required more than 'rds_warn_max_binlog_cache_size' (40960) bytes of storage. Which shall cause replication latency. Please commit it. |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select count(*) from t1;
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.01 sec)

mysql> commit;
Query OK, 0 rows affected (0.01 sec)

mysql> select count(*) from t1;
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.01 sec)

mysql> INSERT INTO t1 VALUES (REPEAT('a',50000));
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message           |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 4008 | Recommend you to INSERT/UPDATE/DELETE rows in batches by multiple transactions. The current transaction required more than 'rds_warn_max_binlog_cache_size' (40960) bytes of storage. Which shall cause replication latency. |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
  2. 查看当前连接的事务Binlog cache大小。 
    mysql> CREATE TABLE t1 (
->   a longtext
-> ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.10 sec)

mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Rds_binlog_trx_cache_size | 0     |
+---------------------------+-------+
1 row in set (0.04 sec)

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
Query OK, 1 row affected (0.01 sec)

mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Rds_binlog_trx_cache_size | 20150 |
+---------------------------+-------+
1 row in set (0.05 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Rds_binlog_trx_cache_size | 0     |
+---------------------------+-------+
1 row in set (0.09 sec)
  3. 查看当前所有连接的事务Binlog cache大小。 
    mysql> SHOW GLOBAL STATUS LIKE 'rds_binlog_trx_cache_size';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Rds_binlog_trx_cache_size | 40300 |
+---------------------------+-------+
1 row in set (0.05 sec)
父主题： 常见内核功能

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