The Ultimate Guide to High Availability with MariaDB
This is a read-only copy of the MariaDB Knowledgebase generated on 2024-11-22. For the latest, interactive version please visit https://mariadb.com/kb/.

ColumnStore Monitor

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 'maxscale'@'maxscalehost' IDENTIFIED BY 'maxscale-password';
GRANT ALL ON infinidb_vtable.* TO 'maxscale'@'maxscalehost';

Master Selection

The ColumnStore Monitor in MaxScale 2.5 supports ColumnStore 1.0, 1.2 and 1.5, and the master selection is done differently for each version.

  • If the version is 1.0, the master server must be specified using the primary parameter.
  • If the version is 1.2, the master server is selected automatically using the ColumnStore function mcsSystemPrimary().
  • If the version is 1.5, the master server is selected automatically by querying the ColumnStore daemon running on each node.

Configuration

Read the Monitor Common document for a list of supported common monitor parameters.

version

With this mandatory parameter the used ColumnStore version is specified. The allowed values are 1.0, 1.2 and 1.5.

primary

Required and only allowed when the value of version is 1.0.

The primary parameter controls which server is chosen as the master server.

If the server pointed to by this parameter is available and is ready to process queries, it receives the Master status.

admin_port

Allowed only when the value of version is 1.5.

This optional parameter specifies the port of the ColumnStore administrative daemon. The default value is 8640. Note that the daemons of all nodes must be listening on the same port.

admin_base_path

Allowed only when the value of version is 1.5.

This optional parameter specifies the base path of the ColumnStore administrative daemon. The default value is /cmapi/0.4.0.

api_key

Allowed only when the value of version is 1.5.

This optional parameter specifies the API key to be used in the communication with the ColumnStore administrative daemon. If no key is specified, then a key will be generated and stored to the file api_key.txt in the directory with the same name as the monitor in data directory of MaxScale. Typically that will be /var/lib/maxscale/<monitor-section>/api_key.txt.

Note that ColumnStore will store the first key provided and thereafter require it, so changing the key requires the resetting of the key on the ColumnStore nodes as well.

local_address

Allowed only when the value of version is 1.5.

With this parameter it is specified what IP MaxScale should tell the ColumnStore nodes it resides at. Either it or local_address at the global level in the MaxScale configuration file must be specified. If both have been specified, then the one specified for the monitor overrides.

Commands

The ColumnStore monitor provides module commands using which the ColumnStore cluster can be managed. The commands can be invoked using the REST-API with a client such as curl or using maxctrl.

All commands require the monitor instance name as the first parameters. Additional parameters must be provided depending on the command.

Note that as maxctrl itself has a timeout of 10 seconds, if a timeout larger than that is provided to any command, the timeout of maxctrl must also be increased. For instance:

maxctrl --timeout 30s call command csmon shutdown CsMonitor 20s

Here a 30 second timeout is specified for maxctrl to ensure that it does not expire before the timeout of 20s provided for the shutdown command possibly does.

The output is always a JSON object.

In the following, assume a configuration like this:

[CsNode1]
type=server
...

[CsNode2]
type=server
...

[CsMonitor]
type=monitor
module=csmon
servers=CsNode1,CsNode2
...

start

Starts the ColumnStore cluster.

call command csmon start <monitor-name> <timeout>

Example

call command csmon start CsMonitor 20s

shutdown

Shuts down the ColumnStore cluster.

call command csmon shutdown <monitor-name> <timeout>

Example

call command csmon shutdown CsMonitor 20s

status

Get the status of the ColumnStore cluster.

call command csmon status <monitor-name> [<server>]

Returns the status of the cluster or the status of a specific server.

Example

call command csmon status CsMonitor
call command csmon status CsMonitor CsNode1

mode-set

Sets the mode of the cluster.

call command csmon mode-set <monitor-name> (readonly|readwrite) <timeout>

Example

call command csmon mode-set CsMonitor readonly 20s

config-get

Returns the cluster configuration.

call command csmon config-get <monitor-name> [<server-name>]

If no server is specified, the configuration is fetched from the first server in the monitor configuration, otherwise from the specified server.

Note that if everything is in order, the returned configuration should be identical regardless of the server it is fetched from.

Example

call command csmon config-get CsMonitor CsNode2

add-node

Adds a new node located on the server at the hostname or IP host to the ColumnStore cluster.

call command csmon add-node <monitor-name> <host> <timeout>

Example

call command csmon add-node CsMonitor mcs2 20s

For a more complete example, please refer to adding a node.

remove-node

Remove the node located on the server at the hostname or IP host from the ColumnStore cluster.

call command csmon remove-node <monitor-name> <host> <timeout>

Example

call command csmon remove-node CsMonitor mcs2 20s

For a more complete example, please refer to removing a node.

Example

The following is an example of a csmon configuration.

[CSMonitor]
type=monitor
module=csmon
version=1.5
servers=CsNode1,CsNode2
user=myuser
password=mypwd
monitor_interval=5000
api_key=somekey1234

Adding a Node

Adding a new node to a ColumnStore cluster can be performed dynamically at runtime, but it must be done in two steps. First, the node is added to ColumnStore and then, the corresponding server object (that possibly has to be created) in the MaxScale configuration is added to the ColumnStore monitor.

In the following, assume a two node ColumnStore cluster and an initial MaxScale configuration like.

[CsNode1]
type=server
...

[CsNode2]
type=server
...

[CsMonitor]
type=monitor
module=csmon
servers=CsNode1,CsNode2
...

Invoking maxctrl list servers will now show:

┌─────────┬─────────────┬──────┬─────────────┬─────────────────┬──────┐
│ Server  │ Address     │ Port │ Connections │ State           │ GTID │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode1 │ 10.10.10.10 │ 3306 │ 0           │ Master, Running │      │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode2 │ 10.10.10.11 │ 3306 │ 0           │ Slave, Running  │      │
└─────────┴─────────────┴──────┴─────────────┴─────────────────┴──────┘

If we now want to add a new ColumnStore node, located at mcs3/10.10.10.12 to the cluster, the steps are as follows.

First the node is added

maxctrl --timeout 30s call command csmon add-node CsMonitor mcs3 20s

After a while the following is output:

{
    "links": {
        "self": "http://localhost:8989/v1/maxscale/modules/csmon/add-node"
    },
    "meta": {
        "message": "Node mcs3 successfully added to cluster.",
        "result": {
            "node_id": "mcs3",
            "timestamp": "2020-08-07 10:03:49.474539"
        },
        "success": true
    }
}

At this point, the ColumnStore cluster consists of three nodes. However, the ColumnStore monitor is not yet aware of the new node.

First we need to create the corresponding server object.

maxctrl create server CsNode3 10.10.10.12

Invoking maxctrl list servers will now show:

┌─────────┬─────────────┬──────┬─────────────┬─────────────────┬──────┐
│ Server  │ Address     │ Port │ Connections │ State           │ GTID │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode3 │ 10.10.10.12 │ 3306 │ 0           │ Down            │      │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode1 │ 10.10.10.10 │ 3306 │ 0           │ Master, Running │      │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode2 │ 10.10.10.11 │ 3306 │ 0           │ Slave, Running  │      │
└─────────┴─────────────┴──────┴─────────────┴─────────────────┴──────┘

The server CsNode3 has been created, but its state is Down since it is not yet being monitored.

┌───────────┬─────────┬──────────────────┐
│ Monitor   │ State   │ Servers          │
├───────────┼─────────┼──────────────────┤
│ CsMonitor │ Running │ CsNode1, CsNode2 │
└───────────┴─────────┴──────────────────┘

It must now be added to the monitor.

maxctrl link monitor CsMonitor CsNode3

Now the server is monitored and maxctrl list monitors shows:

┌───────────┬─────────┬───────────────────────────┐
│ Monitor   │ State   │ Servers                   │
├───────────┼─────────┼───────────────────────────┤
│ CsMonitor │ Running │ CsNode1, CsNode2, CsNode3 │
└───────────┴─────────┴───────────────────────────┘

The state of the new node is now also set correctly, as shown by maxctrl list servers.

┌─────────┬─────────────┬──────┬─────────────┬─────────────────┬──────┐
│ Server  │ Address     │ Port │ Connections │ State           │ GTID │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode3 │ 10.10.10.12 │ 3306 │ 0           │ Slave, Running  │      │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode1 │ 10.10.10.10 │ 3306 │ 0           │ Master, Running │      │
├─────────┼─────────────┼──────┼─────────────┼─────────────────┼──────┤
│ CsNode2 │ 10.10.10.11 │ 3306 │ 0           │ Slave, Running  │      │
└─────────┴─────────────┴──────┴─────────────┴─────────────────┴──────┘

Note that the MaxScale server object can be created at any point, but it must not be added to the monitor before the node has been added to the ColumnStore cluster using call command csmon add-node.

Removing a Node

Removing a node should be performed in the reverse order of how a node was added. First, the MaxScale server should be removed from the monitor. Then, the node should be removed from the ColumnStore cluster.

Suppose we want to remove the ColumnStore node at mcs2/10.10.10.12 and the current situation is as:

┌───────────┬─────────┬───────────────────────────┐
│ Monitor   │ State   │ Servers                   │
├───────────┼─────────┼───────────────────────────┤
│ CsMonitor │ Running │ CsNode1, CsNode2, CsNode3 │
└───────────┴─────────┴───────────────────────────┘

First, the server is removed from the monitor.

maxctrl unlink monitor CsMonitor CsNode3

Checking with maxctrl list monitors we see that the server has indeed been removed.

┌───────────┬─────────┬──────────────────┐
│ Monitor   │ State   │ Servers          │
├───────────┼─────────┼──────────────────┤
│ CsMonitor │ Running │ CsNode1, CsNode2 │
└───────────┴─────────┴──────────────────┘

Now the node can be removed from the cluster itself.

maxctrl --timeout 30s call command csmon remove-node CsMonitor mcs3 20s
{
    "links": {
        "self": "http://localhost:8989/v1/maxscale/modules/csmon/remove-node"
    },
    "meta": {
        "message": "Node mcs3 removed from the cluster.",
        "result": {
            "node_id": "mcs3",
            "timestamp": "2020-08-07 11:41:36.573425"
        },
        "success": true
    }
}
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