mysql5.6 TIME,DATETIME,TIMESTAMP

【背景】

5.6.4以后时间类型（TIME,DATETIME,TIMESTAMP)支持微秒

DATETIME范围：'1000-01-01 00:00:00.000000' to '9999-12-31 23:59:59.999999'

TIMESTAMP范围： values is '1970-01-01 00:00:01.000000' to'2038-01-19 03:14:07.999999'

1) 5.6 支持指定小数精度

use test

CREATE TABLE fractest( c1 TIME(2), c2 DATETIME(2), c3 TIMESTAMP(2) );
INSERT INTO fractest VALUES ('17:51:04.777', '2014-09-08 17:51:04.777', '2014-09-08 17:51:04.777');
SELECT * FROM fractest;

+-------------+------------------------+------------------------+
| c1 | c2 | c3 |
+-------------+------------------------+------------------------+
| 17:51:04.78 | 2014-09-08 17:51:04.78 | 2014-09-08 17:51:04.78 |
+-------------+------------------------+------------------------+

2)5.6.4以前插入的数据支持微秒，但插入存储的数据会忽略微秒

use test

CREATE TABLE fractest( c1 TIME, c2 DATETIME, c3 TIMESTAMP );
INSERT INTO fractest VALUES ('17:51:04.777', '2014-09-08 17:51:04.777', '2014-09-08 17:51:04.777');
SELECT * FROM fractest;

+----------+---------------------+---------------------+
| c1 | c2 | c3 |
+----------+---------------------+---------------------+
| 17:51:04 | 2014-09-08 17:51:04 | 2014-09-08 17:51:04 |
+----------+---------------------+---------------------+

3)5.6时间函数（CURTIME(), SYSDATE(), or UTC_TIMESTAMP()）可以指定微秒精度

mysql> select CURTIME(2);
+-------------+
| CURTIME(2) |
+-------------+
| 11:26:56.43 |
+-------------+

4)存储

5.6.4以前，TIME,DATETIME,TIMESTAMP 分别固定占用3，8，4字节

5.6.4以后，TIME,DATETIME,TIMESTAMP占有大小取决于微秒的精度。

TIME	3 bytes + fractional seconds storage
DATETIME	5 bytes + fractional seconds storage
TIMESTAMP	4 bytes + fractional seconds storage

而微秒的存储长度和精度的关系如下

Fractional Seconds Precision	Storage Required
0	0 bytes
1, 2	1 byte
3, 4	2 bytes
5, 6	3 bytes

例如上例中的c1 TIME：占4字节，c2 DATETIME占6字节,TIMESTAMP 占7字节，TIMESTAMP占用5字节

相关函数可以参考my_datetime_packed_to_binary

5）新老时间类型在源码中的表现

5.6 内部增加了一些新的时间类型

MYSQL_TYPE_TIMESTAMP2

MYSQL_TYPE_DATETIME2,
MYSQL_TYPE_TIME2,

用于支持微秒的存储。

而老的时间类型

MYSQL_TYPE_TIMESTAMP，
MYSQL_TYPE_DATETIME，
MYSQL_TYPE_TIME

仍然保留和支持，从而兼容老的时间数据

5.6 新建的表时间字段默认使用新的类型，参考如下代码

sql/sql_yacc.yy:6514

| DATETIME type_datetime_precision
{ $$= MYSQL_TYPE_DATETIME2; }

6）binlog与新时间类型

binlog的Table_map_log_event中会记录表的元数据信息，包括库，表，列信息等。新时间类型的微秒精度信息就作为列的元数据（m_field_metadata）进行存储。类似的大字段列的列元数据存储大字段的实际长度（Field_blob::do_save_field_metadata）。

【问题重现】

1 master 上执行

use zy

CREATE TABLE t1 (id int primary key, c1 TIME, c2 DATETIME, c3 TIMESTAMP );

set sql_log_bin=0;

alter table t1 modify c3 timestamp(4);

set sql_log_bin=1;

INSERT INTO t1 VALUES (10, '17:51:04.98887', '2014-09-08 17:51:04.866666', '2014-09-08 17:51:04.777');

2 slave上执行

show slave status\G

Last_Errno: 1677

Last_Error: Column 3 of table 'zy.t1' cannot be converted from type 'timestamp' to type 'timestamp'

【分析】

1）先尝试修复，修改slave_type_conversions='ALL_LOSSY';参数slave_type_conversions可以参考 http://dev.mysql.com/doc/refman/5.5/en/replication-options-slave.html#sysvar_slave_type_conversions

mysql> show variables like 'slave_type_conversions';                                                                                          

+------------------------+-------+

| Variable_name          | Value |

+------------------------+-------+

| slave_type_conversions |       |

+------------------------+-------+

1 row in set (0.00 sec) 

mysql> set global slave_type_conversions='ALL_LOSSY';

Query OK, 0 rows affected (0.00 sec)

show slave status\G

  Last_Errno: 1610

  Last_Error: Could not execute Write_rows event on table zy.t1; Corrupted replication event was detected, Error_code: 1610; handler error No Error!; the event's master log mysql-bin.000002, end_log_pos 550

发现备库用备库的表结构信息解析binlog行数据(unpack_row)时出错，因此，此方法修复失败。

2）查看源码：

Rows_log_event::do_apply_event

  table_def::compatible_with

   can_convert_field_to

  ....

   if (field->real_type() == source_type)//本例主备类型一致

  {

    if (metadata == 0) // Metadata can only be zero if no metadata was provided  // 本例主库精度为4

    {

      /*

        If there is no metadata, we either have an old event where no

        metadata were supplied, or a type that does not require any

        metadata. In either case, conversion can be done but no

        conversion table is necessary.

       */

      DBUG_PRINT( "debug" , ("Base types are identical, but there is no metadata"));

      *order_var= 0;

      DBUG_RETURN( true );

    }

    DBUG_PRINT( "debug" , ("Base types are identical, doing field size comparison"));

    if (field->compatible_field_size(metadata, rli, mflags, order_var))

      DBUG_RETURN(is_conversion_ok(*order_var, rli));

    else

      DBUG_RETURN( false );

  }

   else if (metadata == 0 && //这里有对新老时间类型的兼容处理

           ((field->real_type() == MYSQL_TYPE_TIMESTAMP2 &&

             source_type == MYSQL_TYPE_TIMESTAMP) ||

            (field->real_type() == MYSQL_TYPE_TIME2 &&

             source_type == MYSQL_TYPE_TIME) ||

            (field->real_type() == MYSQL_TYPE_DATETIME2 &&

             source_type == MYSQL_TYPE_DATETIME)))

  {

    /*

      TS-TODO: conversion from FSP1>FSP2.

      Can do non-lossy conversion

      from old TIME, TIMESTAMP, DATETIME

      to new TIME(0), TIMESTAMP(0), DATETIME(0).

    */

    *order_var= -1;

    DBUG_RETURN( true);

  }

　　上面代码进行类型兼容性判断，本例由于精度不一致在is_conversion_ok处会返回失败。