docs: durable-execution feasibility study#259
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Evaluate whether PgQue should extend into a durable-workflow engine (DBOS/absurd-style) on Postgres, and the adoption odds if so. Synthesizes deep research on DBOS, absurd, Temporal, Restate, Rivet, and Gadget Silo, grounded against SPECx 2.3 positioning and the PgQ engine constraints. Key finding: the durable layer needs SKIP-LOCKED claim/lease semantics, a second concurrency model beside PgQ rotation, so the zero-bloat differentiator does not transfer. Recommends a thin transactional-durable-enqueue + experimental checkpointed-steps path rather than a head-on Temporal/DBOS competitor.
Earlier draft concluded the zero-bloat differentiator does not transfer to a workflow layer, assuming a mutable workflow_status row updated per step (the DBOS/absurd strategy). That was wrong. Model workflow state transitions as appended events over the rotating log (continuation-passing): each step enqueues its successor instead of mutating a row. Transitions become appends, not UPDATEs, so zero-bloat carries through. Exactly-once handoff falls out of insert_event + finish_batch in one transaction; sleep/timers use the rotating send_at from PR #237; exclusivity is structural via cooperative consumers; the only mutable state is a current-state projection bounded by concurrency. Verdict flips from 'do not compete' to 'compete on a substrate SKIP-LOCKED systems cannot match for high-throughput durable workflows'. Remaining real risk: awaitEvent/join semantics.
Event-sourced durable-execution layer authored with samospec (all-Claude panel). Ships SPEC.md, self-contained HTML brief (BRIEF.html/index.html), and auxiliary artifacts under blueprints/workflows/. .nojekyll added for GitHub Pages.
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What
Adds
blueprints/DURABLE_EXECUTION_FEASIBILITY.md— a strategic evaluation of whether PgQue should extend beyond a queue into a durable-workflow / durable-execution engine on Postgres (DBOS / absurd style), and the realistic adoption odds if it does.Prompted by the HN thread "Building durable workflows on Postgres" (in which PgQue itself is cited for its snapshot+truncate design).
How it was researched
Deep parallel investigation of the six systems the thread orbits — DBOS, absurd, Temporal, Restate, Rivet, Gadget Silo — grounded against
blueprints/SPECx.md§2.3 (workflow engines as a deliberately separate category) andCLAUDE.mdRules #2 (PgQ engine is sacred) and #3 (reduce cleanly to PgQ primitives).Key findings
SELECT … FOR UPDATE SKIP LOCKED+ leases; PgQ uses snapshot+TRUNCATE rotation. A durable layer would need a new claim/lease table beside the engine — a second concurrency model — and the zero-bloat differentiator does not transfer to it.Recommendation
sql/experimental/, single SDK, explicitly labelled — only on real user pull.Verification
Documentation only. No code paths changed; no tests affected.
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