Postgres Transaction ID

Postgres Transaction ID (also known as XID) is a unique identifier assigned to each transaction in a Postgres database. It is used to identify which transaction made a change in the database and is crucial for maintaining the integrity of the data.

How Transaction ID Works

When a transaction starts in Postgres, a new XID is assigned to it. This XID is then used to label all the changes made by that transaction to the database. When the transaction is committed, the XID is recorded in the database's commit log.

If a transaction tries to modify a row that has been modified by another transaction that has not yet committed, Postgres will detect a "transaction conflict". In this case, Postgres will automatically roll back one of the transactions to maintain the database's consistency.

Using Transaction ID in Postgres

Postgres provides two functions to get the current transaction ID: txid_current() and txid_current_snapshot().

SELECT txid_current();

This SQL query will return the current transaction ID.

It's also possible to use the transaction ID to find all the changes made by a specific transaction. For example:

SELECT * FROM my_table WHERE xmin::text = '1234567890';

This SQL query will return all the rows updated or delete by the transaction with XID 1234567890.

Conclusion

Postgres Transaction ID is an essential concept for every developer working with Postgres databases. It's used to maintain the database's consistency and keep track of all the changes made to the data. By understanding how it works and how to use it, developers can build more robust and reliable applications on Postgres databases.