MXS-930: Maxrows filter documentation

MXS-930: Maxrows filter documentation

Documentation/Filters/Maxrows.md

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+# Maxrows
+
+## 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
+```
+
+### Filter Parameters
+
+The maxrows filter has no mandatory parameters.
+Optional parameters are:
+
+#### `max_resultset_rows`
+
+Specifies the maximum number of rows a resultset can have in order to be
+returned to the usere. If a resultset is larger than this an empty result will be sent instead.
+
+```
+max_resultset_rows=1000
+```
+Zero or a negative value is interpreted as no limitation.
+
+The default value is `-1`.
+
+#### `max_resultset_size`
+
+Specifies the maximum size a resultset can have, measured in kibibytes,
+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=128
+```
+The default value is 64.
+
+#### `debug`
+
+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 limit is logged.
+
+Default is `0`. To log everything, give `debug` a value of `3`.
+
+```
+debug=2
+```