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MXS-1506: Document delayed_retry

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Document the parameters and how they interact with `master_reconnection`.
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Markus Mäkelä
2018-04-06 10:11:05 +03:00
parent d80f60e0af
commit 23bc8b6db6
1 changed files with 34 additions and 0 deletions
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Documentation/Routers/ReadWriteSplit.md
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@ -295,6 +295,40 @@ the slave server where the query is being executed fails, readwritesplit can
retry the read on a replacement server. This makes the failure of a slave
transparent to the client.
### `delayed_retry`
Retry queries over a period of time. This parameter takes a boolean value, was
added in Maxscale 2.3.0 and is disabled by default.
When this feature is enabled, a failure to route a query due to a connection
problem will not immediately result in an error. The routing of the query is
delayed until either a valid candidate server is available or the retry timeout
is reached. If a candidate server becomes available before the timeout is
reached, the query is routed normally and no connection error is returned. If no
candidates are found and the timeout is exceeded, the router returns to normal
behavior and returns an error.
When combined with the `master_reconnection` parameter, failures of writes done
outside of transactions can be hidden from the client connection. This allows a
master to be replaced while a write is in progress.
The delayed query retrying mode in readwritesplit does not do any sort of
duplicate write detection. To prevent accidental data duplication, it is highly
recommended to tune the monitor timeouts to values that produce accurate
results.
Duplicate execution of a statement can occur if the connection to the server is
lost or the server crashes but the server comes back up before the timeout for
the retrying is exceeded. At this point, if the server managed to read the
client's statement, it will be executed. For this reason, it is recommended to
only enable `delayed_retry` when the possibility of duplicate statement
execution is an acceptable risk.
### `delayed_retry_timeout`
The number of seconds to wait until an error is returned to the client when
`delayed_retry` is enabled. The default value is 10 seconds.
## Routing hints
The readwritesplit router supports routing hints. For a detailed guide on hint