# ColumnStore Monitor

The ColumnStore monitor, `csmon`, is a monitor module for MariaDB ColumnStore
servers. It supports multiple UM nodes and can detect the correct server for
DML/DDL statements which will be labeled as the master. Other UM nodes will be
used for reads.

## Required Grants

The credentials defined with the `user` and `password` parameters must have all
grants on the `infinidb_vtable` database.

For example, to create a user for this monitor with the required grants execute
the following SQL.

```
CREATE USER 'maxuser'@'%' IDENTIFIED BY 'maxpwd';
GRANT ALL ON infinidb_vtable.* TO 'maxuser'@'%';
```

## Master Selection

The automatic master detection only works with ColumnStore 1.1.7 (planned
version at the time of writing). Older versions of ColumnStore do not implement
the required functionality to automatically detect which of the servers is the
primary UM.

With older versions the `primary` parameter must be defined to tell the monitor
which of the servers is the primary UM node. This guarantees that DDL statements
are only executed on the primary UM.

## Configuration

Read the [Monitor Common](Monitor-Common.md) document for a list of supported
common monitor parameters.

### `primary`

The `primary` parameter controls which server is chosen as the master
server. This is an optional parameter.

If the server pointed to by this parameter is available and is ready to process
queries, it receives the _Master_ status. If the parameter is not defined and
the ColumnStore server does not support the `mcsSystemPrimary` function, no
master server is chosen.

Note that this parameter is only used when the server does not implement the
required functionality. Otherwise the parameter is ignored as the information
from ColumnStore itself is more reliable.

## Example

The following is an example of a `csmon` configuration.

```
[CS-Monitor]
type=monitor
module=csmon
servers=um1,um2,um3
user=myuser
passwd=mypwd
monitor_interval=5000
primary=um1
```

It defines a set of three UMs and defines the UM `um1` as the primary UM.