MySQL 5.6 introduces a new feature – microseconds resolution in some temporal types. As of 5.6.4 TIME, TIMESTAMP and DATETIME can have a fractional part. To create a field with subseconds you can specify precision in brackets: TIME(3), DATETIME(6) etc.
Obviously, the new feature requires the format change. All three types may now have a tail with a fractional part. The tail may be one, two or three bytes long and can store up to six digits after the point.
The non-fractional part has changed too. Thus, DATETIME uses only five bytes comparing to eight in previous versions.
As of revision 79 the recovery toolkit supports the new format.
Let’s recover a sample table to see how it works. The table is
1 2 3 4 5 6 7 8 | CREATE TABLE `t` ( `id` int(11) AUTO_INCREMENT, `t1` time(3), `t2` timestamp(6), `t3` datetime(1), `t4` datetime, PRIMARY KEY (`id`) ) ENGINE=InnoDB |
1 2 3 4 5 6 7 8 9 10 | mysql> select * from t; +----+--------------+----------------------------+-----------------------+---------------------+ | id | t1 | t2 | t3 | t4 | +----+--------------+----------------------------+-----------------------+---------------------+ | 1 | 05:05:10.000 | 2013-07-04 05:05:10.000000 | 2013-07-04 05:05:10.0 | 2013-07-04 05:05:10 | | 2 | 05:14:24.414 | 2013-07-04 05:14:24.125000 | 2013-07-04 05:14:24.4 | 2013-07-04 05:14:25 | | 3 | 05:14:32.566 | 2013-07-04 05:14:32.207031 | 2013-07-04 05:14:32.3 | 2013-07-04 05:14:32 | | 4 | 05:14:34.344 | 2013-07-04 05:14:34.507813 | 2013-07-04 05:14:34.5 | 2013-07-04 05:14:35 | | 5 | 05:14:45.348 | 2013-07-04 05:14:45.832031 | 2013-07-04 05:14:45.1 | 2013-07-04 05:14:45 | +----+--------------+----------------------------+-----------------------+---------------------+ |
First, we should gerenrate a table definition file:
1 | ./create_defs.pl --db test --table t > include/table_defs.h |
Then recompile the tool and split a table space that contains records of the table t:
1 | ./page_parser -f /var/lib/mysql/test/t.ibd |
The next step is to get records from the InnoDB index:
1 2 3 4 5 6 7 8 | $ ./constraints_parser -5f pages-1372929630/FIL_PAGE_INDEX/0-30/00000000-00000003.page 2> /dev/null -- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5) 0000000007DB A6000001A20110 t 1 "05:05:10.0" "2013-07-04 05:05:10.0" "2013-07-04 05:05:10.0" "2013-07-04 05:05:10.0" 0000000007DE A8000001530110 t 2 "05:14:24.4140" "2013-07-04 05:14:24.125000" "2013-07-04 05:14:24.40" "2013-07-04 05:14:25.0" 0000000007EC B2000001A40110 t 3 "05:14:32.5660" "2013-07-04 05:14:32.207031" "2013-07-04 05:14:32.30" "2013-07-04 05:14:32.0" 0000000007ED B3000001A50110 t 4 "05:14:34.3440" "2013-07-04 05:14:34.507813" "2013-07-04 05:14:34.50" "2013-07-04 05:14:35.0" 0000000007FB BD000001670110 t 5 "05:14:45.3480" "2013-07-04 05:14:45.832031" "2013-07-04 05:14:45.10" "2013-07-04 05:14:45.0" -- Page id: 3, Found records: 5, Lost records: NO, Leaf page: YES |
To load this dump use the LOAD DATA INFILE command that’s generated by the contraints_parser, I then redirected it to /dev/null in the example above.
As you can see it’s pretty straightforward. There are two notes:
- Because of format differences the tool can detect whether the field is in the new format or old
- For the TIME field (w/o fractional part) in the new format you need to give a hint to contraints_parser. This is -6 option. Let me illustrate this
Before 5.6.4 TIME was packed in three bytes: DD×24×3600 + HH×3600 + MM×60 + SS. As of 5.6.4 it still uses three bytes, but format is different:
| bits | description | values |
|---|---|---|
| 1 | sign | 1= non-negative, 0= negative |
| 1 | unused | reserved for future extensions |
| 10 | hour | 0-838 |
| 6 | minute | 0-59 |
| 6 | second | 0-59 |
If a field is created without a fractional part it’s impossible to determite the format from a field value. Let’s take a table:
1 2 3 4 5 6 | CREATE TABLE `t` ( `id` int(11) AUTO_INCREMENT, `t1` time , `t2` time(3) , PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
1 2 3 4 5 6 7 8 | mysql> select * from t; +----+----------+--------------+ | id | t1 | t2 | +----+----------+--------------+ | 1 | 11:01:17 | 11:01:17.000 | | 2 | 11:01:17 | 11:01:17.125 | | 3 | 11:01:17 | 11:01:17.125 | +----+----------+--------------+ |
If there is no fractional part constraints_parser assumes old format. So if we try to recover the the records from the table above the result will be wrong:
1 2 3 4 5 6 | $ ./constraints_parser -5f pages-1373023772/FIL_PAGE_INDEX/0-31/00000000-00000003.page -- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (3 3) 000000000807 C5000001AC0110 t8 1 "12:32:17" "11:01:17.0" 000000000807 C5000001AC011C t8 2 "12:32:17" "11:01:17.1250" 000000000807 C5000001AC0128 t8 3 "12:32:17" "11:01:17.1250" -- Page id: 3, Found records: 3, Lost records: NO, Leaf page: YES |
Thus, we need to give a hint, then TIME values are correct:
1 2 3 4 5 6 | ./constraints_parser -5f pages-1373023772/FIL_PAGE_INDEX/0-31/00000000-00000003.page -6 -- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (3 3) 000000000807 C5000001AC0110 t8 1 "11:01:17.0" "11:01:17.0" 000000000807 C5000001AC011C t8 2 "11:01:17.0" "11:01:17.1250" 000000000807 C5000001AC0128 t8 3 "11:01:17.0" "11:01:17.1250" -- Page id: 3, Found records: 3, Lost records: NO, Leaf page: YES |
It is not that obvious that this new feature requires a format change. In fact, microseconds were implemented before MySQL5.6 , in MariaDB 5.3, and this did not require backward-incompatible changes in data representation.
I’m migrating to 5.6 from 5.0 and I have a lot of tables with TIME/TIMESTAMP/DATETIME, but none of them with (number) on their definition.
Do I have to worry? (I’m doing a non-binary upgrade, that is, dumping and load the dump in 5.6)