Decay & dream cycle

Two background processes keep the warm tier from growing unbounded.

Synaptic decay

Every NOVAMEM_DECAY_INTERVAL_MS (default 6 h) the engine sweeps memory_entries and demotes anything past its effective lifespan to cold-only:

effectiveDays(hits) = NOVAMEM_DECAY_DAYS · log₂(hits + 1)

Hits	effectiveDays
0	0 (rare; entries seeded with hits=1 by remember)
1	7
3	14
7	21
15	28
31	35
1023	70

Demotion is cheap: markCold(id, true) flips a flag and the entry stops appearing in keyword search. The vector copy in Qdrant is unchanged — that's still the cold-tier source. The graph node is unchanged.

Reactive promotion

A search hit on a cold-only entry can promote it back to warm if its accumulated lifespan now exceeds its idle days:

if (effectiveDays(preBump.hits + 1) > preBump.idleDays) {
  await this.warm.markCold(id, false);
  this.metrics?.recordPromotion();
}

Without this check, any incidental match would promote — defeating the decay maths. The pre-bump stat read ensures a fresh hit doesn't reset the clock against itself.

Dream cycle

A nightly compaction job (cron-style, configurable via NOVAMEM_DREAM_INTERVAL_MS) runs two passes:

Dedup (cosine + Jaccard)

For each entry pair within a scope:

1. Compute cosine(embedding_a, embedding_b).
2. If cosine ≥ 0.97, also compute tokenJaccard(content_a, content_b).
3. If jaccard ≥ 0.5, merge: keep the older entry, transfer hits from the newer one, delete the newer.

Both gates are required. Cosine alone is fooled by contradictions ("Pascal lives in Dubai" / "Pascal lives in Belgium" — both about Pascal's location, similar vectors). Jaccard's stop-word-filtered token overlap forces the two to share content words, not just structure.

Edge promotion

For nodes with ≥ 3 shared neighbours, add a direct edge between them. Strengthens emergent clusters in the graph; the next graph-tier search hits these stronger paths.

Manual decay

Operator endpoint:

curl -X POST https://novamem.example.com/v1/admin/decay/run \
  -H "Authorization: Bearer ns_..."

Useful right after import / migration when many entries are stale.

Why decay at all?

Without decay, every entry stays warm forever. The warm tier (Postgres) becomes the entire memory; cold (Qdrant) is empty; the tiered architecture collapses. Decay is what makes "tiered" load-bearing — recent + frequent stays fast; everything else is still recallable but doesn't drag down the hot path.

Source

packages/server/src/engine/index.ts — decay(), maybePromote(), dreamCycle().