Hi Rong, It might not be important for the first test implementation, but I'm wondering, does VIDEX intend to handle multi-column hypothetical indexes? I see that videx_build_env.py only collects single-column histograms. If one has histograms on columns A, B, and then tries to produce a multi-column records_in_range estimate for INDEX(A, B), the results may be way off. (and, as a consequence, the page_range problem of records_in_range() would be unimportant in comparison). Is there any way to collect more statistics than what videx_build_env.py does? p.s. I've got a couple more things I'd like to check. I hope I'll get back with those soon. BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Blog: http://petrunia.net