41 lines
980 B
Markdown
41 lines
980 B
Markdown
---
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title: TiDB Transactions (Optimistic vs Pessimistic)
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---
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# TiDB Transactions (Optimistic vs Pessimistic)
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TiDB supports both pessimistic and optimistic transaction modes.
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MySQL/InnoDB users typically expect pessimistic behavior by default.
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## Choose a mode
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- Prefer **pessimistic** when conflicts are common or when the application cannot safely retry on commit failures.
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- Consider **optimistic** when write-write conflicts are rare and you can handle commit failures in the app.
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## Set default mode (cluster-wide)
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```sql
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SET GLOBAL tidb_txn_mode = 'pessimistic';
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-- or:
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SET GLOBAL tidb_txn_mode = 'optimistic';
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```
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## Force mode per transaction
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```sql
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BEGIN PESSIMISTIC;
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-- ... DML ...
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COMMIT;
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```
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```sql
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BEGIN OPTIMISTIC;
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-- ... DML ...
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COMMIT;
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```
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## App-level rule (optimistic)
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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).
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