How Does PostgreSQL's 'timestamp with time zone' Data Type Actually Store Time Zone Information?

Time Zone Storage in PostgreSQL's "timestamp with time zone" Data Type

PostgreSQL differentiates between the timestamp and timestamp with timezone data types. While both occupy 8 bytes, the latter presents a key distinction in how it handles time zone information.

Timestamp Storage

The timestamp data type stores the exact point in time as a UTC timestamp, devoid of any time zone information. This universal time value is then displayed to clients based on their session's current time zone setting.

Time Zone Storage in "timestamp with time zone"

In contrast, the timestamp with timezone data type does not store the actual time zone. Instead, it acts as an offset to compute the UTC timestamp that is stored. When it's read, this offset is used to convert the stored UTC timestamp into the time zone specified in the query or the current session time zone.

Key Considerations

Contrary to its name, the timestamp with timezone type does not store the time zone itself. It merely facilitates the conversion between UTC and local time zones. Additionally, it's worth noting that this data type can exhibit ambiguities due to Daylight Saving Time (DST), making its reliable use questionable.

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