Implement custom commands + parallel custom commands.

src/lua/select_random_ranges.lua

@@ -52,9 +52,11 @@ function thread_init()
    stmt:bind_param(unpack(params))
 
    rlen = sysbench.opt.table_size / sysbench.opt.num_threads
+
+   thread_id = sysbench.tid % sysbench.opt.num_threads
 end
 
-function event(thread_id)
+function event()
    -- To prevent overlapping of our range queries we need to partition the whole
    -- table into num_threads segments and then make each thread work with its
    -- own segment.