MaxScale Maxrows Filter

Limit the size of result sets returned to clients. This filter prevents excessive resource consumption by truncating results that exceed a configured row count.

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

• 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

• 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

_{This page is licensed: CC BY-SA / Gnu FDL}