背景:对tpch的orders进行测试
发现执行计划中的key_skipped_count 令人困惑，不知道真正的含义是什么？
备注:没有删除过数据，tpch的orders的表数据生成以后，就直接count了
mysql> select count() from orders where O_ORDERDATE >= “1995-01-01” and O_ORDERDATE <= “1995-01-03”;
±---------+
| count() |
±---------+
| 1811 |
±---------+
1 row in set (0.00 sec)
mysql> explain analyze select count(*) from orders where O_ORDERDATE >= “1995-01-01” and O_ORDERDATE <= “1995-01-03”;
±----------------------------±--------±--------±----------±---------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±------------------------------------------------±----------±-----+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
±----------------------------±--------±--------±----------±---------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±------------------------------------------------±----------±-----+
| StreamAgg_17 | 1.00 | 1 | root | | time:2.56ms, loops:2 | funcs:count(Column#12)->Column#10 | 388 Bytes | N/A |
| └─IndexReader_18 | 1.00 | 1 | root | | time:2.55ms, loops:2, cop_task: {num: 1, max: 2.49ms, proc_keys: 1811, rpc_num: 1, rpc_time: 2.47ms, copr_cache_hit_ratio: 0.00, distsql_concurrency: 15} | index:StreamAgg_9 | 267 Bytes | N/A |
| └─StreamAgg_9 | 1.00 | 1 | cop[tikv] | | tikv_task:{time:1ms, loops:2}, scan_detail: {total_process_keys: 1811, total_process_keys_size: 83306, total_keys: 1812, get_snapshot_time: 890.3µs, rocksdb: {key_skipped_count: 1811, block: {cache_hit_count: 9}}} | funcs:count(1)->Column#12 | N/A | N/A |
| └─IndexRangeScan_16 | 257.81 | 1811 | cop[tikv] | table:orders, index:O_ORDERDATE(O_ORDERDATE) | tikv_task:{time:1ms, loops:2} | range:[1995-01-01,1995-01-03], keep order:false | N/A | N/A |
±----------------------------±--------±--------±----------±---------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±------------------------------------------------±----------±-----+
4 rows in set (0.01 sec)
