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Everett
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cola_runtime<P, Compose> is a low-level active executor over the existing encoded FC records. I supply Compose from the active sort registry; the immutable world does not choose value semantics. This binary executor transports opaque encoded keys and arrows. The sort-owned runtime uses each sort's physical grammar, and runtime persistence publishes the selected executor's complete frontier.
A contribution creates a queryable immutable snapshot and pays for structural work. A private queue then merges native runs, builds the replacement fractional index, and constructs empty routing carriers as needed. advance performs that work and can return a different physical representation of the same logical state. It does not merely decrease a debt counter.
Here record is an already encoded profile_record. The default merge policy replaces an older value with the newer one. A custom associative policy receives older and newer values in that order, optionally with the key as its first argument. Commutativity is unnecessary. Its encoded result must satisfy the policy's actual value framing. Registry dispatch, tombstone semantics and logical hashes belong to the active handler around this executor.
A snapshot owns its query graph and all native/index dependencies. It contains no mutable job, credit balance or callback. Holding a snapshot while continuing or destroying its executor is safe. from_snapshot(snapshot, compose) starts an independent executor; it does not share a continuation or duplicate existing service credit.
The runtime's graph contains only main routes. Each actual native run covers a contiguous admission interval [first,last). Runs are returned oldest first by snapshot.runs(), while query matches in this particular graph are newest first. The general cola_query_cursor does not promise chronology for arbitrary COLA graphs; the runtime establishes it through these intervals and routes. Replacement reads take the first occurrence. Composition reads fold all occurrences from oldest to newest.
Admission mass counts contributions, including duplicate keys that subsequently coalesce. A settled frontier has strictly decreasing power-of-two masses. An unsettled visible frontier ends with two mass-one runs. Their private carry can merge further equal-mass predecessors before publishing a complete replacement. No partially built native or fractional index becomes visible.
Each published query root fits one K-window. After a carry, empty carriers sample the completed result until it again fits that bound. When selecting a carry's older dependency, the executor may remove empty routing ancestors; it never skips an older native run.
The first backend permits one unsettled admission at a time. The convenience contribute finishes any prior carry before admitting another record. This is conservative synchronous backpressure: a contribution can pay substantial old work. It is not the three-slot schedule's worst-case logarithmic update bound.
A caller that owns a separate debt queue uses:
admission_ready() to test whether a new record can be admitted;try_contribute(record, budget) to refuse without mutation while pending;admission_cost() for the next ready singleton's structural charge, excluding optional service;next_service_cost() for the next indivisible service action's full charge;advance(budget) to add service credit and execute funded actions.advance(0) changes nothing. Insufficient credit remains available for a later call. Publishing the completed carry discards excess credit; a new admission or fork does not inherit it. Calls with different budget partitions perform the same sequence of structural operations. A caller reserving admission resources must not quote old pending work as a constant part of a new record's allowance.
A batch is checked for nondecreasing encoded keys before execution. Equal keys remain separate chronological admissions. Each record receives the supplied service budget; previous pending work is drained between records. An execution failure restores the batch's previous visible snapshot and poisons the active handle. Invalid input rejected during preflight leaves the handle usable.
work() distinguishes cumulative granted credit, consumed structural charges, and successful record/merge/index counters. Charges cover:
| Operation | Structural allowance |
|---|---|
| Native merge initialization | 3 |
| One native merge output step | 3: at most two consumed inputs and one output |
| Native finalization | one per EF sample, plus output ownership setup |
| Fractional-index initialization | 5 |
| One augmented occurrence | 1 occurrence + K target-scan allowance + 5 navigation allowance |
| Index finalization | both borrowed EF sample counts + 3 navigation allowance |
| Snapshot publication | frontier entries + query-chain visits + ownership setup |
Admission also charges singleton native output, its complete tiny index and publication. Its target has at most one sample because the current query root fits K. Job creation charges the copied frontier. admission_cost() calculates these quantities from metadata, rather than assuming a fixed chain depth.
These are conservative structural allowances for executed or attempted operations, not measured CPU instructions or bytes. An allowance can exceed actual work, such as a merge step consuming one input instead of two. Successful record counters are updated only after the corresponding worker step returns; a throwing step may have attempted work covered by its allowance.
Long keys and values, allocation, encoded control lengths and composition callbacks have additional costs. Constructors and EF finalizers execute atomically after their structural allowance is funded. No single-call latency, byte-volume or constant physical-space bound follows from these counters. The count-model scheduler's numerical credit constant is not applied to this backend.
A persistence adapter retains the exact graph plus the oldest-first cola_runtime_interval list. snapshot.admissions() is the final interval end. The immutable nodes expose their owning artifact or mapped pair, native owner, and exact main target, so the adapter can reuse existing files and seal newly built nodes without rewriting unchanged natives.
Wrapping and restoring inspect metadata only. They require an already admitted or explicitly trusted main-only graph. Restore validates interval continuity, power-of-two masses, frontier shape and native counts. It rejects secondary routes: arbitrary COLA graphs need an explicit chronology mapping before they can become runtime frontiers.
This restores an immutable admission frontier, not partial worker state. Pending cleanup restarts from its retained inputs. File/catalog publication, crash reconciliation and resource reservations belong to the durable adapter. A failed executor retains its published snapshot and private input owners; recovery uses a fresh executor from an immutable snapshot.
Questions and patches are welcome at ekmet.nosp@m.t@gm.nosp@m.ail.c.nosp@m.om.
-Edward Kmett
1.9.8