Concurrent transaction serialization and queueing, implicit transactions

An implicit transaction is a single SQL statement that is not framed by a BEGIN statement.

When an implicit transaction fails serialization

The system responds as follows for an implicit transaction that fails serialization:

The system waits for the completion of the transaction that caused the serialization conflict.
After that transaction finishes, either by commit or abort, the system resubmits the waiting requests.

When the number of implicit transactions exceeds the limit

If the system reaches a limit of 63 concurrent read/write transactions and an implicit transaction is issued that attempts to modify data, the system saves and queues the transaction until the number of concurrent read/write transactions falls below the limit.

Modify the default time limit

The system saves and queues implicit transactions for up to 360 minutes (the default). If an implicit transaction waits for more than 360 minutes (or six hours), the transaction fails and returns the error message ERROR: Too many concurrent transactions. You can modify this default timeout setting in two ways:

To set the value for the current session, issue the following command:
```
SET serialization_queue_timeout = <number of minutes>
```
To make the setting global, set the variable serialization_queue_timeout in postgresql.conf.