语法
获取SQL计划信息：
EXPLAIN {LOGICALVIEW | LOGIC | SIMPLE | DETAIL | EXECUTE | PHYSICAL | OPTIMIZER | SHARDING | COST | ANALYZE | BASELINE | JSON_PLAN | ADVISOR} {SELECT statement | DELETE statement | INSERT statement | REPLACE statement| UPDATE statement}
示例
- explain语句：展示基本的SQL执行计划，该执行计划是算子组成，主要体现SQL在CN上的整个执行过程。
mysql> explain select count(*) from lineitem group by L_ORDERKEY;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| LOGICAL EXECUTIONPLAN |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Project(count()="count()") |
| HashAgg(group="L_ORDERKEY", count()="SUM(count())") |
| Gather(concurrent=true) |
| LogicalView(tables="[000000-000003].lineitem_[00-15]", shardCount=16, sql="SELECT `L_ORDERKEY`, COUNT() AS `count()` FROM `lineitem` AS `lineitem` GROUP BY `L_ORDERKEY`") |
| HitCache:false | |
| TemplateId: 5819c807 |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
- 其中，
HitCache标记该查询是否命中PlanCache，取值为falseortrue；TemplateId表示对该计划的标识，具有全局唯一性。 - explain logicalview语句：展示LogicalView所表示的下推SQL在DN上的执行计划。
mysql> explain LOGICALVIEW select mysql> explain select logialview count(*) from lineitem group by L_ORDERKEY;
+----------------------------------------------------------+
| LOGICAL EXECUTIONPLAN |
+----------------------------------------------------------+
| Project(count()="count()") |
| HashAgg(group="L_ORDERKEY", count()="SUM(count())") |
| Gather(concurrent=true) |
| LogicalView |
| MysqlAgg(group="L_ORDERKEY", count(*)="COUNT()") |
| MysqlTableScan(name=[ads, lineitem]) |
| HitCache:true |
| Source:PLAN_CACHE |
| TemplateId: 5819c807
- explain execute语句：表示下推SQL在mysql的执行情况，这个语句和mysql的explain语句同义。通过该语句可以查看下推SQL在DN上有没有使用索引，有没有做全表扫描。
mysql> explain EXECUTE select count(*) from lineitem group by L_ORDERKEY;
+----+-------------+----------+------------+-------+---------------+---------+---------+-----+------+----------+----------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+-------+---------------+---------+---------+-----+------+----------+----------------------------------------------+
| 1 | SIMPLE | lineitem | NULL | index | PRIMARY | PRIMARY | 8 | NULL | 1 | 100 | Using index; Using temporary; Using filesort |
+----+-------------+----------+------------+-------+---------------+---------+---------+-----+------+----------+----------------------------------------------+
1 row in set (0.24 sec)
- explain sharding语句：展示当前查询在DN上扫描的物理分片情况。
mysql> explain sharding select count(*) from lineitem group by L_ORDERKEY;
+---------------+----------------------------------+-------------+-----------+-----------+
| LOGICAL_TABLE | SHARDING | SHARD_COUNT | BROADCAST | CONDITION |
+---------------+----------------------------------+-------------+-----------+-----------+
| lineitem | [000000-000003].lineitem_[00-15] | 16 | false | |
+---------------+----------------------------------+-------------+-----------+-----------+
1 row in set (0.04 sec)
- explain cost语句：相对于explain语句，除了展示执行计划以外，还会显示各个算子基于统计信息估算的代价，以及这条查询被优化器识别的WORKLOAD。
mysql> explain COST select count(*) from lineitem group by L_ORDERKEY;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| LOGICAL EXECUTIONPLAN |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Project(count()="count()"): rowcount = 2508.0, cumulative cost = value = 2.4867663E7, cpu = 112574.0, memory = 88984.0, io = 201.0, net = 4.75, id = 182 |
| HashAgg(group="L_ORDERKEY", count()="SUM(count())"): rowcount = 2508.0, cumulative cost = value = 2.4867662E7, cpu = 112573.0, memory = 88984.0, io = 201.0, net = 4.75, id = 180 |
| Gather(concurrent=true): rowcount = 2508.0, cumulative cost = value = 2.4860069E7, cpu = 105039.0, memory = 29796.0, io = 201.0, net = 4.75, id = 178 |
| LogicalView(tables="[000000-000003].lineitem_[00-15]", shardCount=16, sql="SELECT `L_ORDERKEY`, COUNT() AS `count()` FROM `lineitem` AS `lineitem` GROUP BY `L_ORDERKEY`"): rowcount = 2508.0, cumulative cost = value = 2.4860068E7, cpu = 105038.0, memory = 29796.0, io = 201.0, net = 4.75, id = 109 |
| HitCache:true |
| Source:PLAN_CACHE |
| WorkloadType: TP |
| TemplateId: 5819c807
- explain analyze语句：相对于explain cost语句，除了显示各个算子基于统计信息估算的代价以外，该语句可以收集真实运行过程中算子输出的rowCount等信息。
mysql> explain ANALYZE select count(*) from lineitem group by L_ORDERKEY;
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| LOGICAL EXECUTIONPLAN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Project(count()="count()"): rowcount = 2508.0, cumulative cost = value = 2.4867663E7, cpu = 112574.0, memory = 88984.0, io = 201.0, net = 4.75, actual time = 0.001 + 0.000, actual rowcount = 2506, actual memory = 0, instances = 1, id = 182 |
| HashAgg(group="L_ORDERKEY", count()="SUM(count())"): rowcount = 2508.0, cumulative cost = value = 2.4867662E7, cpu = 112573.0, memory = 88984.0, io = 201.0, net = 4.75, actual time = 0.000 + 0.000, actual rowcount = 2506, actual memory = 0, instances = 1, id = 180 |
| Gather(concurrent=true): rowcount = 2508.0, cumulative cost = value = 2.4860069E7, cpu = 105039.0, memory = 29796.0, io = 201.0, net = 4.75, actual time = 0.000 + 0.000, actual rowcount = 0, actual memory = 0, instances = 0, id = 178 |
| LogicalView(tables="[000000-000003].lineitem_[00-15]", shardCount=16, sql="SELECT `L_ORDERKEY`, COUNT() AS `count()` FROM `lineitem` AS `lineitem` GROUP BY `L_ORDERKEY`"): rowcount = 2508.0, cumulative cost = value = 2.4860068E7, cpu = 105038.0, memory = 29796.0, io = 201.0, net = 4.75, actual time = 0.030 + 0.025, actual rowcount = 10000, actual memory = 0, instances = 0, id = 109 |
| HitCache:true |
| Source:PLAN_CACHE |
| TemplateId: 5819c807 |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
7 rows in set (1.08 sec)
- explain physical语句：展示查询在运行过程中执行模式、各个执行片段（Fragment）的依赖关系和并行度。该查询被识别为单机单线程计划模式（TP_LOCAL），执行计划被分为三个片段Fragment-0、Fragment-1和Fragment-2，先做预聚合再做最终的聚合计算，每个片段的执行度可以不同。
mysql> explain physical select count(*) from lineitem group by L_ORDERKEY;
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| PLAN |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| ExecutorMode: TP_LOCAL |
| Fragment 0 dependency: [] parallelism: 4 |
| Gather(concurrent=true) |
| LogicalView(tables="[000000-000003].lineitem_[00-15]", shardCount=16, sql="SELECT `L_ORDERKEY`, COUNT() AS `count()` FROM `lineitem` AS `lineitem` GROUP BY `L_ORDERKEY`") |
| Fragment 1 dependency: [] parallelism: 8 |
| LocalBuffer |
| RemoteSource(sourceFragmentIds=[0], type=RecordType(INTEGER L_ORDERKEY, BIGINT count(*))) |
| Fragment 2 dependency: [0, 1] parallelism: 8 |
| Project(count()="count()") |
| HashAgg(group="L_ORDERKEY", count()="SUM(count())") |
| RemoteSource(sourceFragmentIds=[1], type=RecordType(INTEGER L_ORDERKEY, BIGINT count(*))) |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
11 rows in set (0.10 sec)
- explain advisor语句：主要是会基于统计信息，分析当前查询的执行计划，给用户推荐可以加速查询的全局二级索引。
mysql> explain advisor select count(*) from lineitem group by L_ORDERKEY \G;
1. row **
IMPROVE_VALUE: 4.4%
IMPROVE_CPU: 340.8%
IMPROVE_MEM: 0.0%
IMPROVE_IO: 1910.0%
IMPROVE_NET: 0.0%
BEFORE_VALUE: 2.48676627E7
BEFORE_CPU: 112573.7
BEFORE_MEM: 88983.8
BEFORE_IO: 201
BEFORE_NET: 4.7
AFTER_VALUE: 2.38256249E7
AFTER_CPU: 25536
AFTER_MEM: 88983.8
AFTER_IO: 10
AFTER_NET: 4.7
ADVISE_INDEX: ALTER TABLE `ads`.`lineitem` ADD GLOBAL INDEX `__advise_index_gsi_lineitem_L_ORDERKEY`(`L_ORDERKEY`) DBPARTITION BY HASH(`L_ORDERKEY`) TBPARTITION BY HASH(`L_ORDERKEY`) TBPARTITIONS 4;
NEW_PLAN:
Project(count()="count()")
HashAgg(group="L_ORDERKEY", count()="SUM(count())")
Gather(concurrent=true)
IndexScan(tables="[000000-000003].lineitem__what_if_gsi_L_ORDERKEY_[00-15]", shardCount=16, sql="SELECT `L_ORDERKEY`, COUNT() AS `count()` FROM `lineitem__what_if_gsi_L_ORDERKEY` AS `lineitem__what_if_gsi_L_ORDERKEY` GROUP BY `L_ORDERKEY`")
INFO: GLOBAL_INDEX
1 row in set (0.13 sec)
