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MXS-1937 Cleanup event handling

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Event handling is now enabled by default. If the monitor cannot query the EVENTS-
table (most likely because of missing credentials), print an error suggesting to
turn the feature off.

When disabling events on a rejoining standalone server (likely a former master),
disable binlog event recording for the session. This prevents the ALTER EVENT
queries from generating binlog events.

Also added documentation and combined similar parts in the code.
This commit is contained in:
Esa Korhonen
2018-09-11 14:22:36 +03:00
parent 4ba0112668
commit cb54880b99
6 changed files with 226 additions and 140 deletions
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20
Documentation/Monitors/MariaDB-Monitor.md
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@ -544,6 +544,26 @@ slave threads are stopped, breaking replication.
promotion_sql_file=/home/root/scripts/promotion.sql
demotion_sql_file=/home/root/scripts/demotion.sql
```
#### `handle_server_events`
This setting is on by default. If enabled, the monitor will attempt to enable
and disable server events during a switchover, failover or rejoin. When a server
is being demoted, any events with "ENABLED" status are set to
"SLAVESIDE_DISABLED". The reverse applies to a server being promoted to master.
When a standalone server is rejoining the cluster, its events are also disabled
since it is now a slave.
The monitor does not enable or disable the event scheduler itself. For the
events to run on the new master server, the scheduler should be enabled by the
admin. Enabling it in the server configuration file is recommended.
Events running at high frequency may cause the replication to break in a
failover scenario. If an old master which was failed over restarts, its event
scheduler will be on if set in the server configuration file. Its events will
also remember their "ENABLED"-status and run when scheduled. This may happen
before the monitor rejoins the server and disables the events. This should only
be an issue for events running more often than the monitor interval or events
that run immediately after the server has restarted.
### Troubleshooting