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The SET TRANSACTION statement sets the transaction priority, access mode, and "as of" timestamp after you BEGIN it but before executing the first statement that manipulates a database.
Synopsis
Required privileges
No privileges are required to set the transaction priority. However, privileges are required for each statement within a transaction.
Parameters
| Parameter | Description |
|---|---|
PRIORITY | If you do not want the transaction to run with NORMAL priority, you can set it to LOW or HIGH.Transactions with higher priority are less likely to need to be retried.For more information, see Transactions: Priorities.The current priority is also exposed as the session variable transaction_priority.Default: NORMAL |
READ | Set the transaction access mode to READ ONLY or READ WRITE. The current transaction access mode is also exposed as the session variable transaction_read_only.Default: READ WRITE |
AS OF SYSTEM TIME | New in v19.1 Execute the transaction using the database contents "as of" a specified time in the past. The AS OF SYSTEM TIME clause can be used only when the transaction is read-only. If the transaction contains any writes, or if the READ WRITE mode is specified, an error will be returned.For more information, see AS OF SYSTEM TIME. |
CockroachDB now only supports SERIALIZABLE isolation, so transactions can no longer be meaningfully set to any other ISOLATION LEVEL. In previous versions of CockroachDB, you could set transactions to SNAPSHOT isolation, but that feature has been removed.
Examples
Set priority
Warning:
This example assumes you're using client-side intervention to handle transaction retries.
> BEGIN;
> SET TRANSACTION PRIORITY HIGH;
> SAVEPOINT cockroach_restart;
> UPDATE products SET inventory = 0 WHERE sku = '8675309';
> INSERT INTO orders (customer, sku, status) VALUES (1001, '8675309', 'new');
> RELEASE SAVEPOINT cockroach_restart;
> COMMIT;
Use the AS OF SYSTEM TIME option
You can execute the transaction using the database contents "as of" a specified time in the past.
> BEGIN;
> SET TRANSACTION AS OF SYSTEM TIME '2019-04-09 18:02:52.0+00:00';
> SELECT * FROM orders;
> SELECT * FROM products;
> COMMIT;
