0-2-1-understand-tl-log-record

name	0.2.1-understand-tl_log_record
description	[0.2.1] The fundamental unit of a transaction_log: a single append-only entry recording one atomic change or lifecycle

understand-tl_log_record

CALL NUMBER: deep_database_transaction.tl_log_record DEFINITION: The fundamental unit of a transaction_log: a single append-only entry recording one atomic change or lifecycle event made by a transaction; identified by an lsn.

Invoke this skill to understand tl_log_record down to its primitives. The RELATIVE ROOT below is the least-fixed-point closure of everything it bundles from — the full import cone, grouped by the lib each prim comes from. Projected from a prover-typed KB (MAP/SWI-Prolog consistency gate): every reference below resolves.

THE RELATIVE ROOT (the import cone, by lib)

from deep_database_transaction

• tl_abort_record (d1): A log_record written when a transaction enters the aborted_state; signals that undo_log entries must be applied to reverse this transaction's effects.
• tl_begin_record (d1): A log_record written when a transaction transitions to the active transaction_state; records transaction_id and start timestamp but no data modifications.
• tl_commit_record (d1): A log_record written when a transaction commits; marks the durable persistence boundary for durability guarantees; flushed to disk before the transaction releases its locks.
• tl_update_record (d1): A log_record capturing a before_image and after_image of a modified data page or row; used by both redo_recovery (for durability) and undo_recovery (for atomicity rollback).
• tl_flush_to_disk (d2): The act of transferring the contents of tl_log_buffer to durable storage; triggered by transaction commit, tl_log_buffer overflow, or a periodic checkpoint; O(1) or O(n) bounded by buffer size.
• tl_redo_log (d2): A log_record or series of tl_update_record entries capturing the after_image of modifications; replayed by recovery_manager to idempotently reconstruct committed changes after a crash.
• tl_undo_log (d2): A structured collection of tl_update_record entries chained by a transaction; traversed in reverse order during rollback to restore the before_image of each modified entity.
• tl_dirty_page_table (d3): A runtime data structure maintained by recovery_manager listing data pages modified but not yet flushed; consulted during checkpoint to ensure write_ahead_logging invariants hold.

CONSUMERS (what needs this)

tl_checkpoint_record, tl_log_buffer, tl_lsn, tl_recovery_manager

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Projected from the database transaction isolation and concurrency control KB (217 concepts / 124 relations) — consistency-typed by MAP; the facet list after the colon IS the cross-lib dependency web.

(leaf — this is an actual skill.)