Timestamp vs. Timestamp with Timezone in PostgreSQL: What's the Real Difference in Storage?

Timestamp Data Types: Delving into Time Zone Storage

The data types timestamp and timestamp with timezone in PostgreSQL share a common storage format, both utilizing 8 bytes. While their names suggest a difference in time zone handling, the true nature of their storage is more intricate.

1. Timestamp: A UTC Representation

Despite its name, the timestamp data type stores only the point in time as a UTC timestamp. It lacks any time zone information. Consequently, the storage requirement is limited to 64 bits, sufficient for representing a specific moment in time.

2. Timestamp with Timezone: A Misnomer

Contrary to its title, the timestamp with timezone data type also stores only the UTC timestamp. It does not retain any time zone information. Instead, it acts as a mechanism to offset the stored UTC timestamp based on the current time zone setting during display.

3. Time Zone Management Outside Storage

Neither of the timestamp data types explicitly stores time zone information. Instead, it is managed outside of the actual storage. When displaying a timestamp with timezone, PostgreSQL will apply the offset based on the session's current time zone setting.

4. Cautions and Best Practices

The time with timezone data type, although defined in the SQL standard, poses challenges due to its potential for ambiguity and difficulty in handling Daylight Saving Time. Its usage is generally discouraged.

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