error : (46) [maxrows] Received data from the backend although we were expecting nothing.

One may get the following error from maxrows filter in MaxScale 2.1.7 with otherwise usual load:

2017-09-13 14:13:13 error : (46) [maxrows] Received data from the backend although we were expecting nothing.

Relevant parts of configuration file are:

[maxscale]

threads=4

...

[Galera Monitor]

type=monitor

module=galeramon

servers=N1, N2, N3

...

[Splitter Service]

type=service

router=readwritesplit

servers=N1, N2, N3

...

max_slave_connections=100%

connection_timeout=5400

disable_sescmd_history=true

max_sescmd_history=5

strict_multi_stmt=false

filters=Hint | MaxRows

[Hint]

type=filter

module=hintfilter

[MaxRows]

type=filter

module=maxrows

max_resultset_rows=300000

max_resultset_size=1T

max_resultset_return=error

...

Hint filter is needed to route SELECT .. FOR UPDATE to master. Everything works without problems when MaxRows filter is not involved.

It would be great to document explicitly when this kind of error may happen and, if possible, prevent it.