Understanding noteworthy error scenarios

After a basic guideline to hunt down the most common issues, this section will discuss some of the most common error scenarios happening in the PostgreSQL world.

Facing clog corruption

PostgreSQL has a thing called commit log, also called 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 PostgreSQL database instance.

In the past, people have reported something called clog corruption...