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Documentation/Routers/SchemaRouter.md
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# SchemaRouter Router
The SchemaRouter router provides an easy and manageable sharding solution by building a single logical database server from multiple separate ones. Each database is shown to the client and queries targeting unique databases are routed to their respective servers. In addition to providing simple database-based sharding, the schemarouter router also enables cross-node session variable usage by routing all queries that modify the session to all nodes.
The SchemaRouter router provides an easy and manageable sharding SOLUTION by
building a single logical database server from multiple separate ones. Each
database is shown to the client and queries targeting unique databases are
routed to their respective servers. In addition to providing simple
database-based sharding, the schemarouter router also enables cross-node
session variable usage by routing all queries that modify the session to all
nodes.
## Routing Logic
If a command line client is used, i.e. `mysql`, and a direct connection to the database is initialized without a default database, the router starts with no default server where the queries are routed. This means that each query that doesn't specify a database is routed to the first available server.
If a command line client is used, i.e. `mysql`, and a direct connection to
the database is initialized without a default database, the router starts
with no default server where the queries are routed. This means that each
query that doesn't specify a database is routed to the first available
server.
If a `USE <database>` query is executed or a default database is defined when connecting to MariaDB MaxScale, all queries without explicitly stated databases will be routed to the server which has this database. If multiple servers have the same database and the user connecting to MariaDB MaxScale has rights to all of them, the database is associated to the first server that responds when the databases are mapped. In practice this means that query results will always come from a single server but the data might not always be from the same node.
If a `USE <database>` query is executed or a default database is defined
when connecting to MariaDB MaxScale, all queries without explicitly stated
databases will be routed to the server which has this database. If multiple
servers have the same database and the user connecting to MariaDB MaxScale
has rights to all of them, the database is associated to the first server
that responds when the databases are mapped. In practice this means that
query results will always come from a single server but the data might not
always be from the same node.
In almost all the cases these can be avoided by proper server configuration and the databases are always mapped to the same servers. More on configuration in the next chapter.
In almost all the cases these can be avoided by proper server configuration
and the databases are always mapped to the same servers. More on
configuration in the next chapter.
## Configuration
@ -23,13 +42,26 @@ user=myuser
passwd=mypwd
```
The module generates the list of databases based on the servers parameter using the connecting client's credentials. The user and passwd parameters define the credentials that are used to fetch the authentication data from the database servers. The credentials used only require the same grants as mentioned in the configuration documentation.
The module generates the list of databases based on the servers parameter
using the connecting client's credentials. The user and passwd parameters
define the credentials that are used to fetch the authentication data from
the database servers. The credentials used only require the same grants as
mentioned in the configuration documentation.
The list of databases is built by sending a SHOW DATABASES query to all the servers. This requires the user to have at least USAGE and SELECT grants on the databases that need be sharded.
The list of databases is built by sending a SHOW DATABASES query to all the
servers. This requires the user to have at least USAGE and SELECT grants on
the databases that need be sharded.
If you are connecting directly to a database or have different users on some of the servers, you need to get the authentication data from all the servers. You can control this with the `auth_all_servers` parameter. With this parameter, MariaDB MaxScale forms a union of all the users and their grants from all the servers. By default, the schemarouter will fetch the authentication data from all servers.
If you are connecting directly to a database or have different users on some
of the servers, you need to get the authentication data from all the
servers. You can control this with the `auth_all_servers` parameter. With
this parameter, MariaDB MaxScale forms a union of all the users and their
grants from all the servers. By default, the schemarouter will fetch the
authentication data from all servers.
For example, if two servers have the database `shard` and the following rights are granted only on one server, all queries targeting the database `shard` would be routed to the server where the grants were given.
For example, if two servers have the database `shard` and the following
rights are granted only on one server, all queries targeting the database
`shard` would be routed to the server where the grants were given.
```
# Execute this on both servers
@ -39,7 +71,11 @@ CREATE USER 'john'@'%' IDENTIFIED BY 'password';
GRANT SELECT,USAGE ON shard.* TO 'john'@'%';
```
This would in effect allow the user 'john' to only see the database 'shard' on this server. Take notice that these grants are matched against MariaDB MaxScale's hostname instead of the client's hostname. Only user authentication uses the client's hostname and all other grants use MariaDB MaxScale's hostname.
This would in effect allow the user 'john' to only see the database 'shard'
on this server. Take notice that these grants are matched against MariaDB
MaxScale's hostname instead of the client's hostname. Only user
authentication uses the client's hostname and all other grants use MariaDB
MaxScale's hostname.
## Router Parameters
@ -49,14 +85,15 @@ List of databases to ignore when checking for duplicate databases.
### `ignore_databases_regex`
Regular expression that is matched against database names when checking for duplicate databases.
Regular expression that is matched against database names when checking for
duplicate databases.
### `preferred_server`
The name of a server in MaxScale which will be used as the preferred server when
a database is found on more than one server. If a database exists on two
servers, of which neither is the server referred by this parameter, the server
that replies first will be assigned as the location of the database.
The name of a server in MaxScale which will be used as the preferred server
when a database is found on more than one server. If a database exists on
two servers, of which neither is the server referred by this parameter, the
server that replies first will be assigned as the location of the database.
This parameter allows deterministic conflict resolution when a sharded cluster
has a central database server and one or more sharded databases spread across
@ -108,8 +145,10 @@ The minimum interval between database map refreshes in seconds.
## Limitations
For a list of schemarouter limitations, please read the [Limitations](../About/Limitations.md) document.
For a list of schemarouter limitations, please read the
[Limitations](../About/Limitations.md) document.
## Examples
[Here](../Tutorials/Simple-Sharding-Tutorial.md) is a small tutorial on how to set up a sharded database.
[Here](../Tutorials/Simple-Sharding-Tutorial.md) is a small tutorial on how
to set up a sharded database.