pages-in-diff-context

page in different context

tags: learning programming database diff-between

content

• the concept page has a few implementations:
  • in OS (mostly referring to memory)
    • normally a page is 4K
  • in storage hardware
    • normally a page is 4K
  • in database
    • in SQLite: 4K, 512B
    • in PostgreSQL: 8K

how to understand pages in these context?

• under all these 3 context, a page is always the smallest unit for storage and I/O
• in OS
  • physical RAM is divided into frames
  • the OS has the concept of pages for virtual memory
  • usually virtual memory’s page is the same size as RAM’s frame
• in hardware
  • a page is the largest unit of data that the device can guarantee failsafe writes
  • (when the hardware writes the data to itself, it’s by the unit of pages. it’s either 1 page or nothing)
• in database
  • the database file is divided into pages
  • when the database needs to write to disks, it’s done by the unit of pages
  • caching, journaling, etc are also done by the unit of pages

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