[fix](scanner) Fix incorrect _max_thread_num in scanner context when many queries are running. #41273 #42014
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…many queries are running. (apache#41273) 1. Minor refactor for scanner constructor, calculation of _max_thread_num is moved to init method 2. The expected value of _max_thread_num is changed. There is no need to submit too many scan task to scan scheduler, since thread num is limited. 3. Calculation of _max_bytes_in_queue is changed. _max_bytes_in_queue for each scan instance is limited to 100MB by default. ``` mysql [tpch]>select count(*) from supplier; -------------- select count(*) from supplier -------------- +----------+ | count(*) | +----------+ | 1000000 | +----------+ 1 row in set (0.04 sec) mysql [tpch]>select count(*) from revenue0; -------------- select count(*) from revenue0 -------------- +----------+ | count(*) | +----------+ | 1000000 | +----------+ 1 row in set (0.19 sec) ``` To illustrate the effect, we need to create much scanners, so ``` set global experimental_parallel_scan_min_rows_per_scanner=29715 ``` default value is `2097152`, we can make scanner num almost equal to `experimental_parallel_scan_max_scanners_count` which is 48. Lets use mysqlslap to do concurrent test. Current master: ```text [hezhiqiang@VM-10-8-centos be_1]$ mysqlslap -hxxxx -uroot -Pyyyy --create-schema=tpch -c 20 -i 5 -q "select s_suppkey, s_name, s_address, s_phone, total_revenue from supplier, revenue0 where s_suppkey = supplier_no and total_revenue = ( select max(total_revenue) from revenue0 ) order by s_suppkey;" Benchmark Average number of seconds to run all queries: 12.480 seconds Minimum number of seconds to run all queries: 12.159 seconds Maximum number of seconds to run all queries: 12.843 seconds Number of clients running queries: 20 Average number of queries per client: 1 [hezhiqiang@VM-10-8-centos be_1]$ mysqlslap -hyyyy -uroot -Pyyyy --create-schema=tpch -c 25 -i 5 -q "select s_suppkey, s_name, s_address, s_phone, total_revenue from supplier, revenue0 where s_suppkey = supplier_no and total_revenue = ( select max(total_revenue) from revenue0 ) order by s_suppkey;" mysqlslap: Cannot run query select s_suppkey, s_name, s_address, s_phone, total_revenue from supplier, revenue0 where s_suppkey = supplier_no and total_revenue = ( select max(total_revenue) from revenue0 ) order by s_suppkey; ERROR : errCode = 2, detailMessage = (10.16.10.8)[TOO_MANY_TASKS]Failed to submit scanner to scanner pool reason:Thread pool Scan_normal is at capacity (192/192 tasks running, 102400/102400 tasks queued)|type:0 ``` After this pr ``` [hezhiqiang@VM-10-8-centos lib]$ mysqlslap -hxxx -uroot -Pxxx --create-schema=tpch -c 50 -i 5 -q "select s_suppkey, s_name, s_address, s_phone, total_revenue from supplier, revenue0 where s_suppkey = supplier_no and total_revenue = ( select max(total_revenue) from revenue0 ) order by s_suppkey;" Benchmark Average number of seconds to run all queries: 31.520 seconds Minimum number of seconds to run all queries: 30.164 seconds Maximum number of seconds to run all queries: 34.131 seconds Number of clients running queries: 50 Average number of queries per client: 1 ``` The max concurrency increased from 25 to 50. Actually, for sequential query test, the performance does not decrease, `submit_many_scan_tasks_for_potential_performance_issue` can be remove in the future.
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cherry pick from #41273