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Multi-version Concurrency Control (cont)

WTS = timestamp of last writer; RTS = timestamp of last reader

Chained tuple versions:   tupoldest → tupolder → tupnewest

When a reader Ti is accessing the database

  • ignore any data item created after Ti started (WTS > TS(Ti))
  • use only newest version V satisfying WTS(V) < TS(Ti)
When a writer Tj attempts to change a data item
  • find newest version V satisfying WTS(V) < TS(Tj)
  • if RTS(V) ≤ TS(Tj), create new version of data item
  • if RTS(V) > TS(Tj), reject the write and abort Tj