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MXS-1549: Add documentation for optimistic_trx

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Added parameter documentation and explained the limitations it has.
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Markus Mäkelä 2018-06-24 10:50:12 +03:00
parent af45006567
commit 391618d53b
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Documentation/Routers/ReadWriteSplit.md
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@ -391,6 +391,29 @@ that exceeds this limit will not be replayed. The default size limit is 1
MiB. Read [the configuration guide](../Getting-Started/Configuration-Guide.md#sizes)
for more details on size type parameters in MaxScale.
### `optimistic_trx`
Enable optimistic transaction execution. This parameter controls whether normal
transactions (i.e. `START TRANSACTION` or `BEGIN`) are load balanced across
slaves. This feature is disabled by default and enabling it implicitly enables
`transaction_replay`, `delayed_retry` and `master_reconnection` parameters.
When this mode is enabled, all transactions are first attempted on slave
servers. If the transaction contains no statements that modify data, it is
completed on the slave. If the transaction contains statements that modify data,
it is rolled back on the slave server and restarted on the master. The rollback
is initiated the moment a data modifying statement is intercepted by
readwritesplit so only read-only statements are executed on slave servers.
As with `transaction_replay` and transactions that are replayed, if the results
returned by the master server are not identical to the ones returned by the
slave up to the point where the first data modifying statement was executed, the
connection is closed. If the execution of ROLLBACK statement on the slave fails,
the connection to that slave is closed.
All limitations that apply to `transaction_replay` also apply to
`optimistic_trx`.
### `causal_reads`
Enable causal reads. This parameter is disabled by default and was introduced in