10月4号
You are using the Performance Schema to investigate replication on a slave which has a single
master. The option slave-parallel-type is set to DATABASE.
Assume that all instruments and consumers are enabled and all threads are instrumented.
Which two facts can be concluded from the given output?
A. The salve has two intermediate relay slaves connected to it.
B. The server needs more cores to use all slave threads.
C. The slave is configured with slave_parallel_workers = 4
D. The slave cannot process the relay log fast enough to use all threads.
E. At most, two schemas are being updates concurrently.
F. THREAD_ID 21 has stopped running.
解析:置参数slave_parallel_workers = 4，即可有4个SQL Thread（coordinator线程）来进行并行复制,
因为slave-parallel-type参数设置为database,因此是按照库进行并发,并发的粒度为schema,有两个线程等待为0,可能没有阻塞,但是并不能说明只有2并发,
Answer: C,D