The transaction ID wraparound in Postgres refers to a situation where the transaction ID space for a database cluster becomes full and can no longer accommodate new transactions. This can happen if the database has been running for a very long time without being restarted, or if it has a very high transaction rate.

To fix this issue, you can restart the database cluster, which will reset the transaction ID counter and allow it to accommodate new transactions. You can also enable automatic vacuum operations, which will periodically clean up old transaction IDs and help prevent the transaction ID space from becoming full.

It is also a good idea to monitor the transaction ID space and make sure that it does not become full. You can do this by running the VACUUM (FULL) command, which will provide information about the current state of the transaction ID space. If it is getting close to becoming full, you can take action to prevent the wraparound from occurring.