How to rollback after commit in PostgreSQL?

@jasen 

To roll back a transaction in PostgreSQL, you can use the ROLLBACK command. This will undo any changes made by the transaction and return the database to the state it was in before the transaction was started.

Here is an example of how to use the ROLLBACK command in PostgreSQL:

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BEGIN;

-- perform some database operations

ROLLBACK;

The BEGIN command starts a new transaction. Any database operations that are performed after the BEGIN command and before the ROLLBACK command will be undone when the ROLLBACK command is executed.

Note that the ROLLBACK command will only roll back changes made within the current transaction. If you have made multiple transactions and want to roll back all of them, you will need to use the ROLLBACK command for each transaction.

It's also worth noting that the ROLLBACK command can only be used to undo changes that have not yet been committed. If you have already committed a transaction, you will not be able to roll it back. In this case, you may need to restore a database backup to revert the changes.

@jasen 

In PostgreSQL, you cannot directly rollback a commit once it has been performed. However, you can use a combination of commands to achieve similar results:

1. Find the target transaction ID (XID) for the commit you want to rollback by running the following query: SELECT xmin, * FROM your_table; Note the transaction ID (XID) of the commit you wish to rollback.
2. Start a new transaction by executing the following command: BEGIN;
3. Use the pg_cancel_backend function to cancel the backend process associated with the target transaction ID obtained in step 1. Replace
4. Rollback the new transaction started in step 2: ROLLBACK;

This process allows you to effectively rollback the changes made by a specific commit by canceling the associated backend process and rolling back the new transaction you've started.

Note: This method is only recommended for situations where you want to undo changes from a recent commit that has not been widely applied or if the changes made by the commit are still pending. Once a commit has been widely applied within the database, it cannot be directly rolled back.