Warning | 1292：Truncated incorrect binlog_cache

binlog_cache_size的大小必须为4096的倍数，不然会有一个warning， “Warning | 1292 | Truncated incorrect binlog_cache_size value: '33792'”，然后向下取最接近n个4096的值。

官方文档上关于binlog_cache_size的描述如下：
binlog_cache_size

Command-Line Format	--binlog_cache_size=#
System Variable	Name	binlog_cache_size
	Variable Scope	Global
	Dynamic Variable	Yes
Permitted Values (32-bit platforms)	Type	integer
	Default	32768
	Min Value	4096
	Max Value	4294967295
Permitted Values (64-bit platforms)	Type	integer
	Default	32768
	Min Value	4096
	Max Value	18446744073709551615

The size of the cache to hold changes to the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large transactions, you can increase this cache size to get better performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 6.4.4, “The Binary Log”.

binlog_cache_size sets the size for the transaction cache only; the size of the statement cache is governed by the binlog_stmt_cache_size system variable.

实验：

mysql> select 4096/1024
    -> ;
+-----------+
| 4096/1024 |
+-----------+
|    4.0000 |
+-----------+
1 row in set (0.00 sec)

mysql> set global binlog_cache_size=1024*4;
Query OK, 0 rows affected (0.00 sec)

mysql> set global binlog_cache_size=1024*8;
Query OK, 0 rows affected (0.00 sec)

mysql> set global binlog_cache_size=1024*4*2;
Query OK, 0 rows affected (0.00 sec)

mysql> set global binlog_cache_size=1024*4*3;
Query OK, 0 rows affected (0.00 sec)

mysql> set global binlog_cache_size=1024*5;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+-----------------------------------------------------+
| Level   | Code | Message                                             |
+---------+------+-----------------------------------------------------+
| Warning | 1292 | Truncated incorrect binlog_cache_size value: '5120' |
+---------+------+-----------------------------------------------------+
1 row in set (0.00 sec)

mysql> set global binlog_cache_size=1024*6;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> set global binlog_cache_size=1024*7;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> set global binlog_cache_size=1024*9;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> set global binlog_cache_size=1024*10;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show variables like 'binlog_cache_size';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| binlog_cache_size | 8192 |
+-------------------+-------+
1 row in set (0.00 sec)

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