Both Percona and Maria allow MySQL to be configured to listen on an extra port when their thread pool is enable.
* https://www.percona.com/doc/percona-server/5.7/performance/threadpool.html
* https://mariadb.com/kb/en/the-mariadb-library/thread-pool-in-mariadb-51-53/
This is valuable because if the table has a lot of traffic (read or write load), gh-ost can end up starving the thread pool as incomming connections are immediately blocked.
By using gh-ost on the extra port, MySQL locking will still behave the same, but MySQL will keep a dedicated thread for each gh-ost connection.
When doing this, it's important to inspect the extra-max-connections variable. Both Percona and Maria default to 1, so gh-ost may easily exceed with its threads.
An example local run using this
```
$ mysql -S /tmp/mysql_sandbox20393.sock -e "select @@global.port, @@global.extra_port"
+---------------+---------------------+
| @@global.port | @@global.extra_port |
+---------------+---------------------+
| 20393 | 30393 |
+---------------+---------------------+
./bin/gh-ost \
--initially-drop-ghost-table \
--initially-drop-old-table \
--assume-rbr \
--port="20395" \
--assume-master-host="127.0.0.1:30393" \
--max-load=Threads_running=25 \
--critical-load=Threads_running=1000 \
--chunk-size=1000 \
--max-lag-millis=1500 \
--user="gh-ost" \
--password="gh-ost" \
--database="test" \
--table="mytable" \
--verbose \
--alter="ADD mynewcol decimal(11,2) DEFAULT 0.0 NOT NULL" \
--exact-rowcount \
--concurrent-rowcount \
--default-retries=120 \
--panic-flag-file=/tmp/ghost.panic.flag \
--postpone-cut-over-flag-file=/tmp/ghost.postpone.flag \
--execute
```
This flag makes migration silently and happily discard any existing foreign keys on migrated table. This is useful for intentional dropping of foreign keys, as gh-ost does not otherwise have support for foreign key migration.
At some time in the future gh-ost may support foreign key migration, at which time this flag will be removed
- Identifying textual characters sets; converting into specific type when applying dml events
- Refactored `ColumnsList`: introducing `Column` type
- Refactored `unsigned` handling, as part of `Column`
- `Column` type supports `convertArg()`: converting value of argument according to column data type
- DB URI attempts `utf8mb4,utf8,latin1` charsets in that order (first one to be recognized wins)
- Local tests filter by pattern
- Local tests append table schema on failure
- Local tests do not have postpone flag file
- Added character set local tests: `utf8`, `utf8mb4`, `latin1`
This helps when the table itself doesn't have foreign keys defined but if there are other tables with foreign keys pointing to the table on which gh-ost runs.
This gives INFO messages for each FK. Note that it now informs the user about `payment` being involved.
```
$ ./gh-ost -database sakila -table rental -alter 'ADD COLUMN ghost_test_001 tinyint DEFAULT NULL' -port 19590 -user msandbox -password msandbox -verbose
2016-08-03 10:18:45 INFO starting gh-ost 1.0.8
2016-08-03 10:18:45 INFO Migrating `sakila`.`rental`
2016-08-03 10:18:45 INFO connection validated on 127.0.0.1:19590
2016-08-03 10:18:45 INFO User has ALL privileges
2016-08-03 10:18:45 INFO binary logs validated on 127.0.0.1:19590
2016-08-03 10:18:45 INFO Restarting replication on 127.0.0.1:19590 to make sure binlog settings apply to replication thread
2016-08-03 10:18:46 INFO Table found. Engine=InnoDB
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`payment` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 ERROR Found 4 foreign keys related to `sakila`.`rental`. Foreign keys are not supported. Bailing out
2016-08-03 10:18:47 FATAL 2016-08-03 10:18:47 ERROR Found 4 foreign keys related to `sakila`.`rental`. Foreign keys are not supported. Bailing out
```
Related Issue: https://github.com/github/gh-ost/issues/129
Related Issue: https://github.com/github/gh-ost/issues/136
New output:
```
2016-08-05 11:39:07 DEBUG Privileges: Super: true, REPLICATION SLAVE: false, ALL on *.*: false, ALL on `sakila`.*: true
2016-08-05 11:39:07 ERROR User has insufficient privileges for migration. Needed: SUPER, REPLICATION SLAVE and ALL on `sakila`.*
2016-08-05 11:39:07 FATAL 2016-08-05 11:39:07 ERROR User has insufficient privileges for migration. Needed: SUPER, REPLICATION SLAVE and ALL on `sakila`.*
```
