# MaxScale Maxrows Filter

## Overview

The Maxrows filter is capable of restricting the amount of rows that a SELECT, a prepared statement or stored procedure could return to the client application.

If a resultset from a backend server has more rows than the configured limit or the resultset size exceeds the configured size, an empty result will be sent to the client.

## Configuration

The Maxrows filter is easy to configure and to add to any existing service.

```
[MaxRows]
type=filter
module=maxrows

[MaxRows-Routing-Service]
type=service
...
filters=MaxRows
```

## Settings

The Maxrows filter has no mandatory parameters. Optional parameters are:

### `max_resultset_rows`

* Type: number
* Mandatory: No
* Dynamic: Yes
* Default: (no limit)

Specifies the maximum number of rows a resultset can have in order to be returned to the user.

If a resultset is larger than this an empty result will be sent instead.

```
max_resultset_rows=1000
```

### `max_resultset_size`

* Type: [size](https://mariadb.com/docs/maxscale/maxscale-management/deployment/installation-and-configuration/maxscale-configuration-guide#sizes)
* Mandatory: No
* Dynamic: Yes
* Default: `64Ki`

Specifies the maximum size a resultset can have in order to be sent to the client. A resultset larger than this, will not be sent: an empty resultset will be sent instead.

```
max_resultset_size=128Ki
```

### `max_resultset_return`

* Type: [enum](https://mariadb.com/docs/maxscale/maxscale-management/deployment/installation-and-configuration/maxscale-configuration-guide#enumerations)
* Mandatory: No
* Dynamic: Yes
* Values: `empty`, `error`, `ok`
* Default: `empty`

Specifies what the filter sends to the client when the rows or size limit is hit, possible values:

* an empty result set
* an error packet with input SQL
* an OK packet

Example output with ERR packet:

```
MariaDB [(test)]> select * from test.t4;
ERROR 1415 (0A000): Row limit/size exceeded for query: select * from test.t4
```

### `debug`

* Type: number
* Mandatory: No
* Dynamic: Yes
* Default: `0`

An integer value, using which the level of debug logging made by the Maxrows filter can be controlled. The value is actually a bitfield with different bits denoting different logging.

* `0` (`0b00000`) No logging is made.
* `1` (`0b00001`) A decision to handle data form server is logged.
* `2` (`0b00010`) Reached max\_resultset\_rows or max\_resultset\_size is logged.

To log everything, give `debug` a value of `3`.

```
debug=2
```

## Example Configuration

Here is an example of filter configuration where the maximum number of returned rows is 10000 and maximum allowed resultset size is 256KB

```
[MaxRows]
type=filter
module=maxrows
max_resultset_rows=10000
max_resultset_size=256000
```

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