Hi all, MonetDB version: 11.23.7 Ubuntu version: 14.04 I created a new optimizer pipeline by adding an additional optimization step after 'default_pipe', i.e.: '*my_customized_pipe*'='optimizer.inline();optimizer.candidates(); optimizer.remap();optimizer.costModel();optimizer.coercions(); optimizer.evaluate();optimizer.pushselect();optimizer.aliases(); optimizer.mitosis();optimizer.mergetable();optimizer.deadcode(); optimizer.aliases();optimizer.constants();optimizer.commonTerms(); optimizer.projectionpath();optimizer.deadcode();optimizer.reorder(); optimizer.reduce();optimizer.matpack();optimizer.dataflow(); optimizer.querylog();optimizer.multiplex();optimizer.generator(); optimizer.profiler();optimizer.garbageCollector(); *optimizer.customizedstep()*' What I have done is: 1) Create an empty optimizer step: -- 1.1 add *opt_customizedstep.c/h* in package *monetdb/optimizer/**, leave function body *OPTcustomizedstepImplementation() *empty*, *i.e. with one statement **return 0** * -- *1.2 register the step by modifying *opt_wrapper.c *and* optimizer.mal* 2) Add the definition of the new pipeline in *opt_pipes.c* 3) Modify the configuration file to compile the added source files. After re-build the system, I can enable the new optimizer pipeline by *set optimizer='my_customized_pipe'*. However, I have two issues: i) using EXPLAIN statement, I found the MAL plan different from the one generated by 'default_pipe' (which should be the same since I did nothing in the added step?). Specifically, the plan seems to be not affected by *optimizer.reorder() *step, i.e., bat.new() and bat.append() instructions appear in the end of the plan. ii) then I entered mdb mode by DEBUG statement. But it seems that some command did not work as before. For example, *help* command does not display all commands available; *optimizer* command does not display actions performed by each optimizer step. What's wrong with my procedure to add a new optimizer pipeline? Any comment would be helpful. Best regards, Wenjian