Table of Contents

Materialised Views

What it shows

A materialised view is an asynchronous, eventually-consistent projection of a source tree, maintained by tailing that tree's write-ahead log. This sample declares two views over a people tree at startup and shows each converging to reflect source writes:

  • A filter / re-project view adults that keeps only people with Age >= 18.
  • An aggregation view age-sum-by-city that sums Age grouped by City.

It seeds five people, waits for the views to catch up, then mutates the source (adds an adult and ages a child past 18) and shows both views re-converging - all without ever writing to a view directly.

Run it

dotnet run --project samples/MaterialisedViews

Expected output

Silo starting... ready.

Writing source people:
  Alice (age 34, London)
  Bob (age 12, London)
  Carol (age 27, Paris)
  Dan (age 9, Paris)
  Eve (age 41, London)

After initial seed - views converged to source:
  'adults' view (3 keys, lag 0):
    Alice (age 34)
    Carol (age 27)
    Eve (age 41)
  'age-sum-by-city' aggregate:
    London: sum(age) = 87
    Paris: sum(age) = 36

Mutating source: add Frank(52, Paris); Bob turns 18 (London).

After mutation - views re-converged:
  'adults' view (5 keys, lag 0):
    Alice (age 34)
    Bob (age 18)
    Carol (age 27)
    Eve (age 41)
    Frank (age 52)
  'age-sum-by-city' aggregate:
    London: sum(age) = 93
    Paris: sum(age) = 88

When to use

  • You need a continuously-maintained secondary index, filtered subset, or rolled-up aggregate of a tree without recomputing it on every read.
  • Consumers can tolerate eventual consistency (bounded apply lag behind the source).

When not to use

  • When you need the value the instant the write commits - a view lags the source. Read the source tree directly for read-your-writes semantics.
  • Views are read-only and derived. Attempting to write to a view-* tree directly through the public ILattice surface is rejected with an InvalidOperationException - change the source and let the view converge. A direct content read of a view-* tree through ILattice is rejected the same way, because a rebuild can swap the view's active generation under a raw handle: read through the ILatticeView handle that ILatticeViewFactory returns, as this sample does.

Notes

  • The views are declared at startup (AddLatticeViews(...)) so their maintainers come online with the host before any writes. WaitForSourceHeadAsync makes the sample deterministic by blocking until the applied frontier reaches the source head; production readers typically just tolerate the small apply lag.

Feature doc