另外sleep函数引发的超内存不触发cancel问题，对于select sleep(1),a.* from table 这种形式，tikv-client堆积大量数据内存使用量超过tidb_mem_quota_query也不会发生oom-kill。
mysql> select count(*) from lineitem_bak;
+-----------+
| count(*) |
+-----------+
| 179998372 |
+-----------+
1 row in set (17.05 sec)
mysql> explain select count(*) from lineitem_bak;
+----------------------------+--------------+-----------+--------------------------------------------+-----------------------------------+
| id | estRows | task | access object | operator info |
+----------------------------+--------------+-----------+--------------------------------------------+-----------------------------------+
| StreamAgg_20 | 1.00 | root | | funcs:count(Column#72)->Column#67 |
| └─IndexReader_21 | 1.00 | root | | index:StreamAgg_8 |
| └─StreamAgg_8 | 1.00 | cop[tikv] | | funcs:count(1)->Column#72 |
| └─IndexFullScan_19 | 179998372.00 | cop[tikv] | table:lineitem_bak, index:idx1(L_SHIPDATE) | keep order:false |
+----------------------------+--------------+-----------+--------------------------------------------+-----------------------------------+
4 rows in set (0.00 sec)
mysql> desc lineitem_bak;
+-----------------+---------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+---------------+------+------+---------+-------+
| L_ORDERKEY | bigint(20) | NO | PRI | NULL | |
| L_PARTKEY | bigint(20) | NO | | NULL | |
| L_SUPPKEY | bigint(20) | NO | | NULL | |
| L_LINENUMBER | bigint(20) | NO | PRI | NULL | |
| L_QUANTITY | decimal(15,2) | NO | | NULL | |
| L_EXTENDEDPRICE | decimal(15,2) | NO | | NULL | |
| L_DISCOUNT | decimal(15,2) | NO | | NULL | |
| L_TAX | decimal(15,2) | NO | | NULL | |
| L_RETURNFLAG | char(1) | NO | | NULL | |
| L_LINESTATUS | char(1) | NO | | NULL | |
| L_SHIPDATE | date | NO | MUL | NULL | |
| L_COMMITDATE | date | NO | | NULL | |
| L_RECEIPTDATE | date | NO | | NULL | |
| L_SHIPINSTRUCT | char(25) | NO | | NULL | |
| L_SHIPMODE | char(10) | NO | | NULL | |
| L_COMMENT | varchar(44) | NO | | NULL | |
| col1 | decimal(15,2) | YES | | NULL | |
| col2 | decimal(15,2) | YES | | NULL | |
| col3 | decimal(15,2) | YES | | NULL | |
| col4 | decimal(15,2) | YES | | NULL | |
| col5 | decimal(15,2) | YES | | NULL | |
| col6 | decimal(15,2) | YES | | NULL | |
| col7 | decimal(15,2) | YES | | NULL | |
| col8 | decimal(15,2) | YES | | NULL | |
| col9 | decimal(15,2) | YES | | NULL | |
| col10 | decimal(15,2) | YES | | NULL | |
| col11 | decimal(15,2) | YES | | NULL | |
| col12 | decimal(15,2) | YES | | NULL | |
| col13 | decimal(15,2) | YES | | NULL | |
| col14 | decimal(15,2) | YES | | NULL | |
| col15 | decimal(15,2) | YES | | NULL | |
| col16 | decimal(15,2) | YES | | NULL | |
| col17 | decimal(15,2) | YES | | NULL | |
| col18 | decimal(15,2) | YES | | NULL | |
| col19 | decimal(15,2) | YES | | NULL | |
| col20 | decimal(15,2) | YES | | NULL | |
| col21 | decimal(15,2) | YES | | NULL | |
| col22 | decimal(15,2) | YES | | NULL | |
| col23 | decimal(15,2) | YES | | NULL | |
| col24 | decimal(15,2) | YES | | NULL | |
| col25 | decimal(15,2) | YES | | NULL | |
| col26 | decimal(15,2) | YES | | NULL | |
| col27 | decimal(15,2) | YES | | NULL | |
| col28 | decimal(15,2) | YES | | NULL | |
| col29 | decimal(15,2) | YES | | NULL | |
| col30 | decimal(15,2) | YES | | NULL | |
| col31 | decimal(15,2) | YES | | NULL | |
| col32 | decimal(15,2) | YES | | NULL | |
| col33 | decimal(15,2) | YES | | NULL | |
| col34 | decimal(15,2) | YES | | NULL | |
| col35 | decimal(15,2) | YES | | NULL | |
| col36 | decimal(15,2) | YES | | NULL | |
| col37 | decimal(15,2) | YES | | NULL | |
| col38 | decimal(15,2) | YES | | NULL | |
| col39 | decimal(15,2) | YES | | NULL | |
| col40 | decimal(15,2) | YES | | NULL | |
| col41 | decimal(15,2) | YES | | NULL | |
| col42 | decimal(15,2) | YES | | NULL | |
| col43 | decimal(15,2) | YES | | NULL | |
| col44 | decimal(15,2) | YES | | NULL | |
| col45 | decimal(15,2) | YES | | NULL | |
| col46 | decimal(15,2) | YES | | NULL | |
| col47 | decimal(15,2) | YES | | NULL | |
| col48 | decimal(15,2) | YES | | NULL | |
| col49 | decimal(15,2) | YES | | NULL | |
| col50 | decimal(15,2) | YES | | NULL | |
+-----------------+---------------+------+------+---------+-------+
66 rows in set (0.00 sec)
mysql> show variables like 'tidb_mem_quota_query';
+----------------------+------------+
| Variable_name | Value |
+----------------------+------------+
| tidb_mem_quota_query | 1073741824 |
+----------------------+------------+
1 row in set (0.00 sec)
mysql> show variables like '%oom%';
+--------------------------------+--------+
| Variable_name | Value |
+--------------------------------+--------+
| tidb_enable_tmp_storage_on_oom | ON |
| tidb_mem_oom_action | CANCEL |
+--------------------------------+--------+
2 rows in set (0.00 sec)
--禁用paging，让tikv-client堆积RPC消息更多
mysql> set tidb_enable_paging=OFF;
Query OK, 0 rows affected (0.00 sec)
--下面语句一直处于执行状态，另起会话观察其内存占用情况
mysql> select sleep(1),a.* from lineitem_bak a;
观察processlist，其用到了15GB还未被kill
mysql> select * from information_schema.processlist where id=937076376958140833\G
*************************** 1. row ***************************
ID: 937076376958140833
USER: root
HOST: 192.168.31.200:50786
DB: tpch
COMMAND: Query
TIME: 251
STATE: autocommit
INFO: select sleep(1),a.* from lineitem_bak a
DIGEST: e08acffb1b819d8e81d84d651cc4e0f4a60e33f04773e58032495900d79da40c
MEM: 15557042042
DISK: 0
TxnStart: 06-11 08:59:55.400(442091489302937601)
1 row in set (0.00 sec)