| name | 0.2.4-understand-rollback |
| description | [0.2.4] The act of undoing a transaction's effects using undo_log entries, returning the database to its pre-transacti |
understand-rollback
CALL NUMBER: database_transaction_isolation_and_concurrency_c.rollback : deep_isolation_level(1)
DEFINITION: The act of undoing a transaction's effects using undo_log entries, returning the database to its pre-transaction state.
Invoke this skill to understand rollback 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 ?
- abort_reason (d2): The specific cause that precipitated a transaction's transition to the aborted_state, such as a constraint violation, deadlock detection timeout, explicit ROLLBACK request, or application-defined failure; distinct from the aborted_state itself which is the terminal condition.
- aborted_data (d2): The intermediate state of rows modified by a transaction that later aborted; the partial_effects_undone that existed between the first write and the rollback completion, representable as before_image/after_image pairs in the undo_log.
- automatic_restart_forbidden (d2): A protocol constraint requiring that a transaction in the aborted_state cannot be re-executed automatically by the database; the application must explicitly reissue the transaction, distinguishing abort from retryable failure.
- lock_release (d2): The deterministic act of relinquishing every lock held by a transaction upon reaching its transaction_boundary, whether through commit or abort, restoring exclusive or shared access rights to the affected rows and index entries for other transactions.
- partial_effects_undone (d2): The invariant that upon rollback all modifications performed by the transaction are reversed to match the before_image recorded in each recovery_log_entry, leaving no residual trace of the transaction's intermediate state in the database.
- recovery_log_entry (d2): A durable record written to the transaction log capturing a single row modification, containing the transaction identifier, the affected row identifier, the before_image, and the after_image; the recovery_subsystem uses these entries to undo uncommitted changes and redo committed changes during crash recovery.
- recovery_subsystem (d3): The database component responsible for restoring consistency after a crash by scanning the transaction log, classifying each transaction as committed uncommitted or aborted, and executing undo operations for uncommitted transactions using their recovery_log_entry records.
from database_transaction_isolation_and_concurrency_c
- aborted_state (d1): The terminal transaction_state after rollback completes; all acquired locks are released and the transaction cannot be restarted automatically.
- transaction_state (d1): The current phase of a transaction lifecycle: active, partially_committed, committed, aborted; drives lock release and recovery behavior.
- transaction_id (d2): A monotonically increasing identifier assigned to each transaction; the basis for snapshot_isolation read_view construction and visibility_check.
- committed (d2): The terminal transaction_state after durable persistence of all changes; locks are released per locking_protocol rules.
from deep_isolation_level
- committed_data (d3): database state resulting from successfully completed transactions; constitutes the visible universe for read_committed queries
CONSUMERS (what needs this)
atomicity, before_image, compensation, compensation_action, database_transaction, transaction_boundary
Projected from the database transaction isolation and concurrency control KB (280 concepts / 214 relations) — consistency-typed by MAP; the facet list after the colon IS the cross-lib dependency web.
(leaf — this is an actual skill.)
