Verify your knowledge

• What is a transaction?

  A transaction is a unit of work that is either consolidated or discarded as a whole. A transaction can be made by a single statement or multiple statements and can be implicit or explicit. See the Introducing transactions section for more details.

• What is an xid and to which problem is it subject?

  An xid is a transaction identifier, a number that uniquely represents a transaction within the whole cluster. Being stored as a counter, the value is subject to the so-called problem of xid wraparound, which VACUUM and autovacuum freezing solve. See the More about transaction identifiers – the XID wraparound problem section for more details.

• What is MVCC?

  MVCC is a technique by which, at a given instant, multiple versions of a tuple can exist within a database. Depending on the currently running transactions and their commit status, a different version is used. See the Explaining MVCC...