Using Hints in DBLE to Control Routing and Execute Custom SQL

In previous sessions we introduced the Global table and ER table; in addition, DBLE provides a hint feature to specify routing.

What is a Hint A hint is an effective comment that allows a business application to designate a specific shard, enabling the middleware to dispatch SQL in the designated way. The hint contains routing results, for example ID=1, and after the routing calculation the actual SQL executed may be different, but the hint conveys the routing intention.

For example, the statement insert xx select * from xxx is not currently supported by DBLE, but the same effect can be achieved through a hint, which specifies the routing result while the actual executed SQL may differ.

Hint Classification

DBLE hints are divided into several types: one that calculates routing via SQL, one that directly specifies the target node, and a third type that forces a SELECT to read from the primary node in a read‑write split scenario.

Operation Demonstration We demonstrate using a hint with a stored procedure. Using the DBLE MySQL client, we look at table tb_mod which contains five rows. Suppose we want to delete data on a specific node; the process is simple: we issue a delete * from tb_mod statement preceded by a hint that points to tb_mod=1 . After executing the stored‑procedure call, the rows with IDs 1 and 5 are removed. This shows how hints can direct execution to a particular node for operations that DBLE does not natively support, such as insert select * from table and similar statements.

That concludes the introduction for today.

For easier reading, some colloquial wording has been optimized without affecting learning; the text and video aim to stay consistent.

DBLE and related project code repositories: https://github.com/actiontech/dble https://github.com/actiontech/dble-docs-cn https://github.com/actiontech/dble-test-suite

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