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Merge branch '2.2' into develop

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Johan Wikman
2018-05-21 10:06:20 +03:00
parent 4788c4947d 76f32a38ac
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Documentation/Routers/ReadWriteSplit.md
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@ -154,6 +154,30 @@ reported by the server itself.
`LEAST_BEHIND_MASTER` does not take server weights into account when choosing a
server.
#### Server Weights and `slave_selection_criteria`
The following formula is used to calculate a score for a server when the
`weightby` parameter is defined.
```
score = x / w
```
`x` is the absolute value of the chosen metric (queries, connections) and
`w` is the weight of the server. The value of `w` is the relative weight
of the server in relation to all the servers configured for the
service. The server with the highest score that fulfills all other
criteria is chosen as the target server.
Read the [configuration guide](../Getting-Started/Configuration-Guide.md#weightby)
for a more detailed example on how the weights are calculated.
For `LEAST_CURRENT_OPERATIONS`, the metric is number of active queries on
the candidate server, for `LEAST_GLOBAL_CONNECTIONS` and
`LEAST_ROUTER_CONNECTIONS` it is the number of open connections and for
`LEAST_BEHIND_MASTER` it is the number of seconds a server is behind the
master.
#### Interaction Between `slave_selection_criteria` and `max_slave_connections`
Depending on the value of `max_slave_connections`, the slave selection criteria