> ## Documentation Index
> Fetch the complete documentation index at: https://cockroachlabs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# SET TRANSACTION
export const InternalLink = ({version, path = "", children, ...props}) => {
let detectedVersion = version || "stable";
if (typeof window !== 'undefined' && !version) {
const match = window.location.pathname.match(/\/docs\/([^/]+)/);
if (match) {
detectedVersion = match[1];
}
}
const normalizedPath = path.startsWith("/") ? path.slice(1) : path;
return
{children}
;
};
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 read-only 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` | 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`. |
| `NOT DEFERRABLE`
`DEFERRABLE` | This clause is supported for compatibility with PostgreSQL. `NOT DEFERRABLE` is a no-op and the default behavior for CockroachDB. `DEFERRABLE` returns an `unimplemented` error. |
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
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> BEGIN;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SET TRANSACTION PRIORITY HIGH;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SAVEPOINT cockroach_restart;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> UPDATE products SET inventory = 0 WHERE sku = '8675309';
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO orders (customer, sku, status) VALUES (1001, '8675309', 'new');
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> RELEASE SAVEPOINT cockroach_restart;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> 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.
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> BEGIN;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SET TRANSACTION AS OF SYSTEM TIME '2019-04-09 18:02:52.0+00:00';
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SELECT * FROM orders;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SELECT * FROM products;
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> COMMIT;
```
### Set the default transaction priority for a session
To set the default transaction priority for all transactions in a session, use the `default_transaction_priority` session variable. For example:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SET default_transaction_priority 'high';
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SHOW transaction_priority;
```
```
transaction_priority
------------------------
high
```
Note that `transaction_priority` is a read-only session variable that cannot be set directly.
## See also
* `SET`
* Transactions: Priority levels
* `BEGIN`
* `COMMIT`
* `SAVEPOINT`
* `RELEASE SAVEPOINT`
* `ROLLBACK`