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Everything is an event

Every memory is an append-only event with a ULID, a type, content, an importance score, a timestamp, access counters, and a tier. Events aren’t edited in place: an update appends a new event, and a removal either archives (soft delete) or purges (hard delete). That keeps history honest and recovery easy.

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Types of memory

PMB separates memory by type so the agent can treat each kind with the right weight.

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Facts that change: keyed facts

Some facts have exactly one current value - your city, your employer, a pet’s name. record_keyed_fact stores these as (subject, attribute, value) and upserts: writing a new value archives the old one, so recall returns only the current value while the history stays queryable.

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Importance, pinning, and forgetting

Importance

Every event has a 0.0-1.0 score that drives ranking and decay. Defaults vary by type - a fact starts higher than a routine activity.

Pin

Pinning locks a memory at max importance; a pinned memory is never auto-archived.

Forgetting curve

A daily decay lowers importance over time; old, low-importance memory is eventually archived. Tune with decay.factor_per_day or run pmb decay.

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Three tiers: how fast memory fades

Every event sits in one of three tiers that differ only in fade speed. Recalling a memory promotes it toward a slower-fading tier - what you use sticks, what you never touch decays.

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Soft delete vs hard delete

Archiving (soft delete) hides a memory from recall but keeps the row, so you can restore it. A hard delete purges the row, its search vector, and its graph links. See Deleting memories.