Visibility Map in Postgres

[japananh]

Visibility Map in Postgres

The Visibility Map is a bitmap associated with each table in PostgreSQL, where each bit corresponds to a table data page. The VM tracks which pages in a table contain only tuples (rows) visible to all active transactions.

In the bitmap:

• A set bit means that all tuples on the page are visible to all transactions.
• An unset bit means the page might contain some tuples that are not visible to all transactions.

Ref: https://www.postgresql.org/docs/current/storage-vm.html