Glossary

Living glossary of MortarMQ terminology and naming. The governing rule: same meaning, same name; different meaning, different name.

1. On-Disk Format Magics

Rule: MM prefix + a 2–3 letter category code. Every persistent file format gets its own magic; magics are never reused, and the version field immediately follows the magic. New formats must be registered in this table before they are implemented.

Magic	File	Mnemonic
MMQS	Partition segment (message log segment)	Queue Segment
MMQC	Partition checkpoint	Queue Checkpoint
MMML	Metadata log (source-of-truth metadata log)	Meta Mutation Log
MMMS	Metadata snapshot (mmms-<offset>-<epoch>.bin)	Meta Metastate
MMLQ	Delivery ledger (delivery.mql)	Ledger (Queue delivery semantics)
MMCU	Cursor checkpoint (cursor.mqc)	Cursor
MMDL	DLQ envelope	Dead Letter
MMCUP	Follower catch-up state	Catch-up

Historical erratum: the object diagram once mistyped MMRS (corrected to MMQS on 2026-10-01). This table is the yardstick for catching such errors.

2. Epoch / Sequence Naming

The easiest naming pairs to get wrong in this project:

Term	Semantics
cluster_epoch	Static membership-configuration version
leader_epoch	Replication-group leader version (increments after Prepare/Install); the fencing boundary
promised_leader_epoch	Locally persisted promise watermark
membership_epoch	Version of the member set (increments on join/leave/subscription change)
assignment_epoch	Target-assignment version
installed_assignment_epoch	The assignment version a member has installed (⚠️ formerly member_epoch; renamed 2026-10-01 because it differed from membership_epoch by only 4 characters while being semantically orthogonal. The wire field name remains assignment_epoch)
ownership_epoch	Single-partition ownership version (consumer-side fencing)
wholesale_ownership_epoch	Wholesale ownership generation of one subscription — the value CREDIT.ownership_epoch carries. Advances only when a subscription's ownership set is replaced whole (revoke-all / loss / rejoin), never on a partial partition migration; the retired generation's tombstone outlives member lifecycles
cursor_epoch	Cursor-checkpoint version
mutation_id	Monotonic metadata-mutation number (failover floor)
commit_seq / visible_seq	Quorum commit point / consumer-visible ceiling
last_appended / flushed_seq	Local write point / local durability point
ack_floor / next_scan / first_retained_seq	Contiguous-ack watermark / scan position / retention start
delivery_id	Id of one delivery instance (consumer-side fencing — not the business idempotency key)
producer_id / producer_seq	Producer idempotency key (use this pair for business dedup, not delivery_id)

Fence repair order: fence_operation checks generation first (0x0020 StaleGeneration), ownership second (0x0021 NotOwner), recency third (0x0022 StaleOwner); a request that fails several fences reports the earliest — the first repair the client must make. Table of record: broker/epoch_model.mbt.

3. ID System Map

The numbered IDs that recur across this site. Each one is either defined on a page that ships here or labels something on a page that ships here — no ID in this documentation refers to a document outside this repository.

Prefix	Meaning
UC1–UC12	Use cases (diagrams)
INV-001…INV-014	Invariant register (single source of truth across all three methodologies)
CM / CB / CL / CF / CS / CQ	Property suites: metrics conservation / rebalance / clock / frame / client state machine / quorum consistency
Golden n	Per-component golden cases
P0 / P1 / P2	Priority tier: P0 blocks the work that depends on it, P1 must close before that work starts, P2 needs a probe first
0x0/2/4/6xxx	Four error-code segments (protocol / metadata / backpressure / replication) — see Error Code Registry

4. Backlog

To be added as they stabilize: the 19 config allowlist names, the 15 metric names, and the TSV column names for the 7 CLI commands. All three are machine-readable; this glossary only hosts abbreviations that recur in conversation.