Understanding noteworthy error scenarios

After those basic guidelines to hunt down the most common issues, the upcoming sections will discuss some of the most common error scenarios happening in the PostgreSQL world.

Facing clog corruption

PostgreSQL has a thing called the commit log (now called pg_xact; it is formally known as pg_clog). It tracks the state of every transaction on the system and helps PostgreSQL determine whether a row can be seen or not. In general, a transaction can be in four states:

#define TRANSACTION_STATUS_IN_PROGRESS    0x00
#define TRANSACTION_STATUS_COMMITTED      0x01
#define TRANSACTION_STATUS_ABORTED        0x02
#define TRANSACTION_STATUS_SUB_COMMITTED  0x03

The clog has a separate directory in the...