Table of Contents

Change History

What it shows

Every write to a lattice key becomes a revision in that key's timeline. ILattice.ScanEntryHistoryAsync reads that timeline back, oldest first, so you can answer "how did this value get here?" for any key. This sample writes five successive values to a single key and then prints the full revision timeline - each revision's hybrid-logical-clock stamp, kind, value length, and content hash - alongside a plain GetAsync that only ever sees the latest value. It uses the zero-setup WAL-window fallback (no durable history view configured), so Source is reported as WalWindow.

Run it

dotnet run --project samples/ChangeHistory

Expected output

Silo starting... ready.

Writing 5 successive revisions to key 'order-42':
  set 'order-42' = 'placed'
  set 'order-42' = 'paid'
  set 'order-42' = 'packed'
  set 'order-42' = 'shipped'
  set 'order-42' = 'delivered'

Plain GetAsync('order-42') -> 'delivered' (latest only)

ScanEntryHistoryAsync('order-42') - the revision timeline:
  #1 hlc=HLC(639186130401564317:0) kind=Set valueLen=6 valueHash=0x9c47e7c2cd8e44a
  #2 hlc=HLC(639186130401883202:0) kind=Set valueLen=4 valueHash=0x9cf71314683dc6c2
  #3 hlc=HLC(639186130401922192:0) kind=Set valueLen=6 valueHash=0xaf49d4d5d84095
  #4 hlc=HLC(639186130401939858:0) kind=Set valueLen=7 valueHash=0xeb8bd0214fed79e0
  #5 hlc=HLC(639186130401948855:0) kind=Set valueLen=9 valueHash=0x89bb07d314f252a7

Source=WalWindow (WalWindow = best-effort fallback, no history view enabled)
Truncated=False (true would mean older revisions were already trimmed by WAL GC)
Total revisions read: 5

(Clock values differ per run.)

When to use

  • Ad-hoc inspection of how a key evolved, with no configuration or extra storage.
  • Debugging or audit spot-checks where the recent WAL window is enough.

When not to use

  • When you need a complete, retention-bounded audit trail. The WAL fallback is bounded by WAL garbage collection, so older revisions may already be trimmed (page.Truncated == true). Enable a durable history view for that - it reports Source == View and is never truncated below its configured retention age.

Feature doc