Illumio Administration Guide 25.4

Symptom:

The PCE stores data in PostgreSQL databases. Under certain conditions, PostgreSQL may issue warnings about transaction ID wraparound.

In illumio-pce.log and postgresql.log, look for messages like the following:

ERROR: database is not accepting commands to avoid wraparound data loss in database "<database_name>"

Stop the postmaster and vacuum that database in single-user mode.

Cause:

In a PostgreSQL database, transaction wraparound (also known as transaction ID exhaustion) can occur if many transactions have occurred and the transaction ID reaches its maximum possible value and is forced to begin again at zero. As a result, transactions from the past suddenly have a higher transaction ID than the current ID, and therefore appear to be in the future – and therefore inaccessible. The result is extreme loss of data. The database stops accepting requests. Instilling commands manually is the only way to recover from a transaction ID wraparound.

To avoid this situation, PostgreSQL provides an autovacuum feature that recovers disk space by removing dead row versions before transaction ID wraparound can occur. The PCE databases use the PostgreSQL autovacuum feature to prevent transaction wraparound. However, in the following situations, autovacuum might not succeed:

For details about autovacuum and transaction ID wraparound, see the PostgreSQL documentation page Preventing Transaction ID Wraparound Failures.

Monitoring and Diagnosis:

Use the dbcheck tool to periodically monitor the system for early detection of any potential transaction ID wraparound condition. It is vital to act before the situation develops into a transaction ID wraparound failure.