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.
Map the durable-workflow design to pgque's real primitives and verify the keystone against sql/pgque.sql: insert_event + finish_batch compose atomically in the caller transaction (exactly-once handoff), finish_batch is one subscription UPDATE per batch (amortization), ev_extra1..4 are settable+indexable (workflow_id lookup). Flags the retry_queue DELETE-bloat constraint (route sleeps through rotating send_at, PR #237), gives the new coordination DDL, concrete awaitEvent/emit + join SQL, a bloat audit, and the pgque gaps to close (promote send_at, ev_extra1 index, durable.sql).
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What
Refreshes the durable-execution feasibility draft and workflow spec after review of Microsoft
pg_durableand after checking PR #259 for internal mismatches.What changed
pg_durableas fresh prior art and records the product boundary: workflow durability in Postgres, workflow code in app repositories.blueprints/workflows/HOT_PATH_BENCHMARK.md, the first gate for the batching question: compare mutableworkflow_statusupdates vs PgQue continuation events, plus dedup andwf_livevariants.workflow_idcapability model: raw ids exist in protected hot queue rows /ev_extra1; lower-trust audit, DLQ, metrics, and error/export surfaces must hash or truncate.Why
The old PR body and generated spec bundle contradicted the revised feasibility doc, and the draft predated
pg_durable, which is now the most relevant fresh prior art for Postgres-native durable execution.The new hot-path benchmark doc exists because the whole workflow idea lives or dies on one narrow claim: N workflow step-events in one PgQue batch should append N successors and advance the subscription once, without recreating per-workflow update churn.
Verification
Documentation only.
git diff --checkrgscan for stale active claims / architecture placeholderCurrent status
Keep as draft. The feasibility doc is useful now; the next real gate is the hot-path benchmark/prototype, not merging a claim.