Some of what you know has a shelf life

Two facts, two lifespans

“David prefers parallel delegation” and “the sync service is running” are both facts, but they age on completely different clocks. The first is durable: it holds until someone decides otherwise. The second is volatile: it was true when it was checked, may be false an hour later, and — the dangerous part — nobody will file an update when it flips. A memory that scores both by the same slow clock will keep handing you the volatile one long after it went wrong.

Age-decay is the wrong tool for volatile facts

Letting knowledge fade over months is exactly right for durable facts that stop being renewed. It is useless for “is the daemon up.” You do not want that to slowly lose confidence over half a year — you want it treated as unverified within hours, and you want to be told to re-check it. Decay answers a different question (“is this getting old?”) than volatility does (“has this been confirmed recently enough to rely on?”).

Mark it, then re-check just it

The move is small. Tag the time-varying facts for what they are, give them a freshness window, and let the memory surface the handful that have gone past it — these need a re-check — instead of re-examining the whole corpus. You re-verify a few operational facts; you do not relitigate every decision you ever recorded.

And re-checking a volatile fact and finding it still true is real evidence, not noise — it refreshes the fact’s currency. This is the one place where saying the same thing again is valuable rather than redundant, and a memory worth trusting knows the difference.

Why this keeps the memory honest

The failure it prevents runs both ways. Without it you trust stale facts — the service “is running” when it crashed an hour ago. But you also wrongly distrust still-true ones — you assume a connection got fixed because something upstream changed, when the specific thing never did. Both are errors of currency, and you only catch them by re-verifying the parts of the world that move.

So the durable facts hold, and the moving ones get checked. That division is what lets a shared memory stay current without drowning you in re-confirmation — forgetting what should fade, and re-asking only what genuinely might have changed.

Frequently asked

Related