THE FOLD / RESPAWN / ROLLBACK / THE JOURNAL
THE JOURNAL
not indivisible - survivable to do twice
1 WHAT IT IS · WHAT IT DOES · FACT OR FICTION
A journal makes an update survivable by doing it twice: describe the change in a log, commit the log, then apply it where it belongs. The log is not the data. The log is the promise that the data can be reconstructed.
LIT verified live. Updating in place has 3 crash points and survives 2 — 66.7%; the one it loses is mid-overwrite, where the page is neither old nor new. The journal has 4 crash points and survives all 4: before commit it rolls back, after commit it replays. For 1,000 page updates that costs 8,192,000 bytes written against 4,096,000 — exactly 2×, every byte written twice.
LIT verified live. Updating in place has 3 crash points and survives 2 — 66.7%; the one it loses is mid-overwrite, where the page is neither old nor new. The journal has 4 crash points and survives all 4: before commit it rolls back, after commit it replays. For 1,000 page updates that costs 8,192,000 bytes written against 4,096,000 — exactly 2×, every byte written twice.
2 HOW IT WAS WEAVED · AI + HUMAN
Write-ahead logging is ARIES’ shape and it is under every serious database and journaling filesystem.
AVAN (AI) first computed the recovery number with a contrived loop that produced a plausible figure without modelling anything. It was replaced with an explicit list of the crash points and what each one leaves behind, so the claim is readable rather than merely correct-looking. The commit record is the whole mechanism: it is the single point where the outcome flips from “forget it” to “finish it”.
AVAN (AI) first computed the recovery number with a contrived loop that produced a plausible figure without modelling anything. It was replaced with an explicit list of the crash points and what each one leaves behind, so the claim is readable rather than merely correct-looking. The commit record is the whole mechanism: it is the single point where the outcome flips from “forget it” to “finish it”.
3 ONE DIMENSION
Every crash point, and what recovery finds.
4 TWO DIMENSIONS · INTERACTIVE
Crash at each step and see what recovery can do.
5 THREE DIMENSIONS + AVAN’S INVERSE
The green forward object: a promise written before the fact.
AVAN’s addition (the inverse-companion): the forward reading is that the journal buys correctness with a 2× write cost. The inverse is that it does not make the update atomic — it makes the update repeatable. Nothing here happens all at once; the page is still overwritten non-atomically at the end, and a crash during that leaves the same torn page as before. What changed is that the log still says what it was supposed to become. Read backwards, durability is not achieved by making an operation indivisible; it is achieved by making it survivable to do the same thing twice.
LIT updating in place has 3 crash points and survives 2 of them at 66.7%, losing the one mid-overwrite where the page is neither old nor new, while a write-ahead log has 4 crash points and survives all 4 - rolling back before the commit and replaying after it - at a cost for 1,000 page updates of 8,192,000 bytes against 4,096,000, exactly 2x, every byte written twice
FIG Write-ahead logging is ARIES' shape and it is under every serious database and journaling filesystem. AVAN first computed the recovery number with a contrived loop that produced a plausible figure without modelling anything; it was replaced with an explicit list of the crash points and what each leaves behind, so the claim is readable rather than merely correct-looking. The commit record is the whole mechanism.
FIG Write-ahead logging is ARIES' shape and it is under every serious database and journaling filesystem. AVAN first computed the recovery number with a contrived loop that produced a plausible figure without modelling anything; it was replaced with an explicit list of the crash points and what each leaves behind, so the claim is readable rather than merely correct-looking. The commit record is the whole mechanism.
◆ sealed .dlw.fold → folded to ROOT_0 · a sphere of ROLLBACK · David Lee Wise (ROOT0), with AVAN