go__cache/docs

Gache notions

Basic idea

Like Memcached, plus...

• Usability:
  • True FLUSHALL
  • Single process for multiple bins
• Management
  • Complete locking dump/restore
  • Snapshots
• Tag support
• Pluggable storage
  • Journaling
  • Write-back/write-through replication
  • Chained storage (fast → slow)

But probably slower overall, just more convenient.

Components

• Protocol handling (FSMs)
  • Application: Memcache protocol proper
  • Presentation: ASCII / Binary
  • Transport:
  • TCP with persistent connections
  • TCP without persistent connections
  • UDP
  • raw socketpair (stdin/stdout)
• Readline equivalence for ASCII presentation interactions
• Storage
  • Pluggable storage
  • Journaling
  • Storage engines
  • Memory
  • Memcached, for use as a debugging proxy in front of a standard instance
  • Others ?
  • Memory
    • Main memory allocation
    • Slab allocator
  • Reporting
  • Background expiration lurker

Memory allocation

Memcache slabs model

• http://www.mikeperham.com/2009/06/22/slabs-pages-chunks-and-memcached/ (2009)
  • Older versions of memcached used slabs sized based on powers of two, so you'd have a 1KB slab, 2KB slab, 4KB slab, ..., all the way to 1MB.
  • Newer (2006: 1.2.0-RC1 ?) versions use 1.25^n for the chunk size
• Allocate slabs for elements of a given size range ("chunks")
• Slabs are made of fixed-size (1MB) pages, split according to the chunk size
• Slab chunk sizes are in a geometric progression: (1 + x)^n