mysql> explain analyze select sum(L_EXTENDEDPRICE) from lineitem;
+----------------------------+------------+---------+-----------+----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------+-----------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+----------------------------+------------+---------+-----------+----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------+-----------+------+
| HashAgg_11 | 1.00 | 1 | root | | time:1.37s, loops:2, partial_worker:{wall_time:1.366558591s, concurrency:5, task_num:1, tot_wait:6.832190204s, tot_exec:31.755µs, tot_time:6.832224842s, max:1.366448056s, p95:1.366448056s}, final_worker:{wall_time:0s, concurrency:5, task_num:1, tot_wait:6.832286057s, tot_exec:16.792µs, tot_time:6.832305524s, max:1.366465061s, p95:1.366465061s} | funcs:sum(Column#18)->Column#17 | 20.2 KB | N/A |
| └─TableReader_12 | 1.00 | 13 | root | | time:1.37s, loops:2, cop_task: {num: 13, max: 1.37s, min: 708.7ms, avg: 998.8ms, p95: 1.37s, max_proc_keys: 467326, p95_proc_keys: 467326, tot_proc: 12.9s, tot_wait: 55ms, rpc_num: 13, rpc_time: 13s, copr_cache_hit_ratio: 0.00, distsql_concurrency: 15} | data:HashAgg_5 | 436 Bytes | N/A |
| └─HashAgg_5 | 1.00 | 13 | cop[tikv] | | tikv_task:{proc max:1.36s, min:687ms, avg: 985.2ms, p80:1.07s, p95:1.36s, iters:5869, tasks:13}, scan_detail: {total_process_keys: 6001215, total_process_keys_size: 1166860203, total_keys: 6001228, get_snapshot_time: 59.8ms, rocksdb: {key_skipped_count: 6001215, block: {cache_hit_count: 43, read_count: 18391, read_byte: 554.2 MB, read_time: 877.6ms}}} | funcs:sum(tpch1.lineitem.l_extendedprice)->Column#18 | N/A | N/A |
| └─TableFullScan_10 | 6622334.00 | 6001215 | cop[tikv] | table:lineitem | tikv_task:{proc max:1.28s, min:630ms, avg: 924.2ms, p80:1.02s, p95:1.28s, iters:5869, tasks:13} | keep order:false | N/A | N/A |
+----------------------------+------------+---------+-----------+----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------+-----------+------+
4 rows in set (1.37 sec)
block: {cache_hit_count: 43, read_count: 18391, read_byte: 554.2 MB, read_time: 877.6ms} 这种带有read_count才是发生物理读吧，我帖子中的那个只有逻辑读。
另外这种慢的情况并不是特殊情况，是普遍情况，所以你随便自己做个环境测试就能测试出来。