Hi Rong, Short: I've found a limitation in VIDEX which isn't mentioned on its homepage. Are you aware of this? The good part here is that when one hits the limitation the server returns an error (instead of silently prodicing a wrong query plan). Long: I was looking at VIDEX and got this question: MariaDB (and MySQL) optimizer may read individual table rows for constant tables, and further optimization makes use of the column values it has read. How does VIDEX deal with this situation? It looks like it doesn't. A basic example using the test dataset. Assume the VIDEX is set up as shown in README.md. Let's first try a query using a real table: mysql> use tpch_tiny; Database changed mysql> explain select count(*) from customer,orders where c_custkey=o_custkey and c_custkey=150000; +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | no matching row in const table | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+--------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> Then, let's try VIDEX: mysql> use videx_tpch_tiny; Database changed mysql> explain select count(*) from customer,orders where c_custkey=o_custkey and c_custkey=150000; ERROR 1031 (HY000): Table storage engine for 'customer' doesn't have this option One can say this query is not very meaningful but that's just a basic example. One may construct more meaningful examples. Another example similar to the above: mysql> explain select * from customer where c_custkey= (select max(c_custkey) from customer); ERROR 1031 (HY000): Table storage engine for 'customer' doesn't have this option BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Blog: http://petrunia.net