openclaw/skills/tidb-sql/references/transactions.md

title
TiDB Transactions (Optimistic vs Pessimistic)

TiDB Transactions (Optimistic vs Pessimistic)

TiDB supports both pessimistic and optimistic transaction modes. MySQL/InnoDB users typically expect pessimistic behavior by default.

Choose a mode

• Prefer pessimistic when conflicts are common or when the application cannot safely retry on commit failures.
• Consider optimistic when write-write conflicts are rare and you can handle commit failures in the app.

Set default mode (cluster-wide)

SET GLOBAL tidb_txn_mode = 'pessimistic';
-- or:
SET GLOBAL tidb_txn_mode = 'optimistic';

Force mode per transaction

BEGIN PESSIMISTIC;
-- ... DML ...
COMMIT;

BEGIN OPTIMISTIC;
-- ... DML ...
COMMIT;

App-level rule (optimistic)

If you generate SQL intended for optimistic transactions, require the caller/application to handle COMMIT errors and retry the whole transaction safely (idempotency + retry loop).