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MXS-2362 Document SchemaRouter table-sharding limitations

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Esa Korhonen
2019-03-07 13:33:03 +02:00
parent c8078c99e5
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Documentation/Routers/SchemaRouter.md
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@ -139,24 +139,20 @@ refresh_interval=60
This functionality was introduced in 2.3.0. This functionality was introduced in 2.3.0.
If the same database exists on multiple servers, but the database contains If the same database exists on multiple servers, but the database contains different
different tables in each server, the SchemaRouter is capable of tables in each server, SchemaRouter is capable of routing queries to the right server,
transparently routing queries to the right server, depending on which table depending on which table is being addressed.
is being addressed.
For instance, suppose the database `db` exists on servers _server1_ and As an example, suppose the database `db` exists on servers _server1_ and _server2_, but
_server2_, but that the database on _server1_ contains the table `tbl1` and that the database on _server1_ contains the table `tbl1` and on _server2_ contains the
on _server2_ contains the table `tbl2`. table `tbl2`. The query `SELECT * FROM db.tbl1` will be routed to _server1_ and the query
`SELECT * FROM db.tbl2` will be routed to _server2_. As in the example queries, the table
In that case, the query names must be qualified with the database names for table-level sharding to work.
Specifically, the query series below is not supported.
``` ```
SELECT * FROM db.tbl1 USE db;
SELECT * FROM tbl1; // May be routed to an incorrect backend if using table sharding.
``` ```
will be routed to _server1_ and the query
```
SELECT * FROM db.tbl2
```
will be routed to _server2_.
## Router Options ## Router Options