特性描述
SQL PATCH主要设计给DBA、运维人员及其他需要对SQL进行调优的角色使用，用户通过其他运维视图或定位手段识别到业务语句存在计划不优导致的性能问题时，可以通过创建SQL PATCH对业务语句进行基于Hint的调优。目前支持行数、扫描方式、连接方式、连接顺序、PBE custom/generic计划选择、语句级参数设置、参数化路径的Hint。此外，对于部分由特定语句触发系统内部问题导致系统可服务性受损的语句，在不对业务语句变更的情况下，也可以通过创建用于单点规避的SQL PATCH，对问题场景提前报错处理，避免更大的损失。
SQL PATCH的实现当前基于Unique SQL ID，所以需要打开相关的运维参数才可以生效（详见特性约束），Unique SQL ID在WDR报告和慢SQL视图中都可以获取到，在创建SQL PATCH时需要指定Unique SQL ID。下面给出简单的使用样例。
场景一：使用SQL PATCH对特定语句进行Hint调优。
openGauss=# set track_stmt_stat_level = 'L1,L1'; --打开FullSQL统计信息
SET
openGauss=# select * from hint_t1 t1 where t1.a = 1; --执行SQL语句
a | b | c
---+---+---
1 | 1 | 1
(1 row)
openGauss=# select unique_query_id, query, query_plan from dbe_perf.statement_history where query like '%hint_t1%'; --获取查询计划和Unique SQL ID
-[ RECORD 1 ]---+----------------------------------------------------------------------------------------------
unique_query_id | 2578396627
query | select * from hint_t1 t1 where t1.a = ?;
query_plan | Datanode Name: sgnode
| Bitmap Heap Scan on hint_t1 t1 (cost=4.33..15.70 rows=10 p-time=0 p-rows=0 width=12)
| Recheck Cond: (a = '***')
| -> Bitmap Index Scan on hint_t1_a_idx (cost=0.00..4.33 rows=10 p-time=0 p-rows=0 width=0)
| Index Cond: (a = '***')
|
|
openGauss=# select * from dbe_sql_util.create_hint_sql_patch('patch1', 2578396627, 'indexscan(t1)'); -- 对指定的Unique SQL ID指定Hint Patch
-[ RECORD 1 ]---------+--
create_hint_sql_patch | t
openGauss=# explain select * from hint_t1 t1 where t1.a = 1; -- 通过explain可以确认Hint是否生效
NOTICE: Plan influenced by SQL hint patch
QUERY PLAN
-----------------------------------------------------------------------------------
[Bypass]
Index Scan using hint_t1_a_idx on hint_t1 t1 (cost=0.00..32.43 rows=10 width=12)
Index Cond: (a = 1)
(3 rows)
openGauss=# select * from hint_t1 t1 where t1.a = 1; -- 再次执行语句
a | b | c
---+---+---
1 | 1 | 1
(1 row)
openGauss=# select unique_query_id, query, query_plan from dbe_perf.statement_history where query like '%hint_t1%'; -- 可以看到新的执行记录计划已改变
-[ RECORD 1 ]---+--------------------------------------------------------------------------------------------------
unique_query_id | 2578396627
query | select * from hint_t1 t1 where t1.a = ?;
query_plan | Datanode Name: sgnode
| Bitmap Heap Scan on hint_t1 t1 (cost=4.33..15.70 rows=10 p-time=0 p-rows=0 width=12)
| Recheck Cond: (a = '***')
| -> Bitmap Index Scan on hint_t1_a_idx (cost=0.00..4.33 rows=10 p-time=0 p-rows=0 width=0)
| Index Cond: (a = '***')
|
|
-[ RECORD 2 ]---+--------------------------------------------------------------------------------------------------
unique_query_id | 2578396627
query | select * from hint_t1 t1 where t1.a = ?;
query_plan | Datanode Name: sgnode
| Index Scan using hint_t1_a_idx on hint_t1 t1 (cost=0.00..8.27 rows=1 p-time=0 p-rows=0 width=12)
| Index Cond: (a = '***')
|
|
场景二：使用SQL PATCH对特定语句进行提前报错规避。
openGauss=# select * from dbe_sql_util.drop_sql_patch('patch1'); -- 删去patch1
drop_sql_patch
----------------
t
(1 row)
openGauss=# select * from dbe_sql_util.create_abort_sql_patch('patch2', 2578396627); 对该语句的Unique SQL ID创建Abort Patch
create_abort_sql_patch
------------------------
t
(1 row)
openGauss=# select * from hint_t1 t1 where t1.a = 1; -- 再次执行语句会提前报错
ERROR: Statement 2578396627 canceled by abort patch patch2
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