logical-replicationlisted

PostgreSQL's logical replication — publisher-side WAL decoding + subscriber-side apply — plus everything under `src/backend/replication/logical/`. Loads when the user asks about logical decoding, `pg_logical_slot_get_changes`, publications / subscriptions, output plugins (pgoutput / test_decoding), reorder buffer, historic snapshots (SnapBuild), the apply worker + parallel apply, conflict resolution (PG 18+ conflict tracking), replication origins, replication slots (physical vs logical, `slot.c` + `slotsync.c`), streaming mode for in-progress transactions, tablesync's initial COPY, or debugging apply-worker crashes / slot advancement / catalog_xmin retention. Skip when the ask is about physical streaming replication (walsender/walreceiver, `replication/basebackup*.c`, `replication/walsender.c` in isolation) — those are the sibling `replication` subsystem, mostly disjoint code paths.
matejformanek/postgres-claude · ★ 0 · AI & Automation · score 70

Install: claude install-skill matejformanek/postgres-claude

# logical-replication — logical decoding + apply Logical replication has **two sides** you must not confuse: - **Publisher side** — reads WAL, decodes it into logical changes, hands them to an *output plugin* (usually `pgoutput`) which serializes them as protocol messages sent over a walsender. - **Subscriber side** — the *apply worker* receives those messages, applies INSERT/UPDATE/DELETE to the local database, and tracks its progress via a *replication origin*. Both live under `src/backend/replication/logical/` (20 files). Neither is a simple codebase — `worker.c` alone is 194 KB; `reorderbuffer.c` is 162 KB. ## The file map ### Publisher (decoding) side | File | KB | Role | |---|---:|---| | `decode.c` | 40 | WAL-record-to-logical-change decoder. Reads XLogRecords, dispatches to reorderbuffer callbacks. | | `reorderbuffer.c` | 162 | The **big one**. Assembles decoded changes into transaction-shaped batches, spills to disk on memory pressure, handles subtransactions, TOAST reassembly, streaming (in-progress) transactions. | | `snapbuild.c` | 65 | Historic-snapshot construction — SnapBuild state machine (BUILDING → FULL_SNAPSHOT → CONSISTENT) that lets decoding see committed catalog state as of a chosen LSN. | | `logical.c` | 69 | Logical-decoding context (`LogicalDecodingContext`), CreateInitDecodingContext (for slot creation), CreateDecodingContext (for reading). | | `logicalctl.c` | 21 | Utilities for the logical-decoding control interface. | | `logicalfuncs.c` | 10