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Heaps in PostgreSQL (cont)

PostgreSQL "heap file" may use multiple physical files
  • files are named after the OID of the corresponding table
  • first data file is called simply OID
  • if size exceeds 1GB, create a fork called OID.1
  • add more forks as data size grows (one fork for each 1GB)
  • other files:
    • free space map (OID_fsm), visibility map (OID_vm)
    • optionally, TOAST file (if table has varlen attributes)
  • for details: Chapter 55 in PostgreSQL documentation