tuichenchuxin opened a new issue, #20736:
URL: https://github.com/apache/shardingsphere/issues/20736
## Feature Request
We have `HintManager` for users to use for hint route, But it's depends on
`ThreadLocal`.
We want to use SQL hint to replace HintManager for more convenient to use.
## replace `HintManager.setDatabaseShardingValue`
```
/* SHARDINGSPHERE_HINT: SHARDING_DATABASE_VALUE=1 */
SELECT * FROM t_order,t_order_item;
```
## replace `HintManager.addDatabaseShardingValue`
`HintManager.addTableShardingValue`
```
/* SHARDINGSPHERE_HINT:
t_order.SHARDING_DATABASE_VALUE=100,t_order.SHARDING_TABLE_VALUE=100 */
SELECT * FROM t_order,t_order_item;
```
## replace `HintManager.setWriteRouteOnly` mix sharding
```
/* SHARDINGSPHERE_HINT:
t_order.SHARDING_DATABASE_VALUE=100,t_order.SHARDING_TABLE_VALUE=100,t_order_item.SHARDING_DATABASE_VALUE=100,WRITE_ROUTE_ONLY=true
*/
SELECT * FROM t_order,t_order_item;
```
## for better performance
Since we have SQL parse cache, shardingSphere have a good performance. But
if we have same SQL with different comment, we can not use the parse cache. So
it's better to extract hint in proxy and jdbc, and remove the hint message from
sql before parsing sql.
## tasks
- [ ] support sql hint for sharding
- [ ] refactor sql hint for readwrite
- [ ] move shadow comment extracted to sql hint
- [ ] better performance for sql hint
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