Some last info: the problem disappears when using the no_mitosis_pipe optimizer pipeline. sql>set optimizer='no_mitosis_pipe'; operation successful (0.139ms) sql>SELECT * FROM source1 WHERE SUBSTRING(SOURCE,1,2)='04' LIMIT 1 OFFSET 400000; +-----------------------------------------------------------------------------+--------+----------------------------------------------------------------------------------------------------------------------------------------------------+ | file | line | source | +=============================================================================+========+====================================================================================================================================================+ | /home/bkaptijn/DDDB/.tmpinputdir/9772_9999_20130501_20130531_Schade_516.ASC | 430664 | 04999999999999999999999999999999999999999 : +-----------------------------------------------------------------------------+--------+----------------------------------------------------------------------------------------------------------------------------------------------------+ 1 tuple (1.1s) sql>set optimizer='default_pipe'; operation successful (0.305ms) sql>SELECT * FROM source1 WHERE SUBSTRING(SOURCE,1,2)='04' LIMIT 1 OFFSET 400000; +------+------+--------+ | file | line | source | +======+======+========+ +------+------+--------+ 0 tuples (798.870ms) Regards, Bas