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MXS-1639 Add documentation on promotion/demotion sql files

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Esa Korhonen
2018-04-23 14:51:33 +03:00
parent 5cf56c7c0f
commit 2aeed3ffab
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Documentation/Monitors/MariaDB-Monitor.md
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@ -287,6 +287,10 @@ With `auto_rejoin` active, the monitor will try to rejoin any server matching
the above requirements. When activating rejoin manually, the user-designated
server must fulfill the same requirements.
The user can define files with SQL statements which are executed on any server
being demoted or promoted by cluster manipulation commands. See the sections on
`promotion_sql_file` and `demotion_sql_file` for more information.
### Limitations and requirements
Switchover and failover only understand simple topologies. They will not work if
@ -440,6 +444,35 @@ replication to break.
servers_no_promotion=backup_dc_server1,backup_dc_server2
```
#### `promotion_sql_file` and `demotion_sql_file`
These are paths to text files with SQL statements in them. During promotion or
demotion, the contents are read line-by-line and executed on the backend. Empty
lines or lines starting with '#' are ignored. All statements must succeed and
none may return results, otherwise the switchover or failover fails.
When promoting a slave to master during switchover or failover, the
`promotion_sql_file` is read and executed on the new master server after its
read-only flag is disabled. The commands are ran *before* starting replication
from an external master if any.
`demotion_sql_file` is ran on an old master during demotion to slave, before the
old master starts replicating from the new master. The file is also ran before
rejoining a standalone server to the cluster, as the standalone server is
typically a former master server.
Since the queries in the files are ran during operations which modify
replication topology, care is required. If `promotion_sql_file` contains data
modification (DML) queries, the new master server may not be able to
successfully replicate from an external master. `demotion_sql_file` should never
contain DML queries, as these may not replicate to the slave servers before
slave threads are stopped, breaking replication.
```
promotion_sql_file=/home/root/scripts/promotion.sql
demotion_sql_file=/home/root/scripts/demotion.sql
```
### Manual switchover and failover
Both failover and switchover can be activated manually through the REST API or