| name | 0.1.4-understand-read_committed |
| description | [0.1.4] An isolation_level where each statement sees only data committed before that statement begins; prevents dirty_ |
understand-read_committed
CALL NUMBER: database_transaction_isolation_and_concurrency_c.read_committed : deep_database_transaction(6), deep_isolation_level(4)
DEFINITION: An isolation_level where each statement sees only data committed before that statement begins; prevents dirty_read but allows non_repeatable_read and phantom_read.
Invoke this skill to understand read_committed 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 database_transaction_isolation_and_concurrency_c
- dirty_read (d1): An anomaly where a transaction reads data written by another transaction that has not yet committed; only possible in read_uncommitted.
- isolation_level (d1): A configurable parameter defining the degree to which concurrent transactions are isolated from each other's uncommitted or intermediate effects.
- non_repeatable_read (d1): An anomaly where a transaction reads the same row twice and gets different values because another transaction modified and committed between reads.
- phantom_read (d1): An anomaly where a transaction re-executes a range query and gets a different set of rows due to another transaction inserting or deleting rows in that range.
- read_uncommitted (d2): The weakest isolation_level: transactions may observe uncommitted changes from other transactions, permitting dirty_read.
- repeatable_read (d2): An isolation_level ensuring that all reads within a transaction see a consistent snapshot as of transaction start; prevents non_repeatable_read but may permit phantom_read.
- serializable (d2): The strongest isolation_level: the result of executing concurrent transactions is equivalent to some serial order of those transactions; prevents all anomalies.
- snapshot_isolation (d2): An isolation_level using mvcc where a transaction reads from a consistent snapshot taken at transaction start; prevents lost_update but allows write_skew.
- atomicity (d2): The all-or-nothing property: a transaction's effects are either fully applied or fully absent; implemented via undo_log and transaction rollback.
- commit (d3): The act of making a transaction's effects permanent: flush log records to durable storage, release locks, transition transaction_state to committed.
- rollback (d3): The act of undoing a transaction's effects using undo_log entries, returning the database to its pre-transaction state.
- transaction_log (d3): An append-only sequence of records tracking every change made by transactions; the primary mechanism for atomicity and durability.
- transaction_state (d3): The current phase of a transaction lifecycle: active, partially_committed, committed, aborted; drives lock release and recovery behavior.
- undo_log (d3): Log records describing the previous state of modified data; used to undo uncommitted transaction changes during rollback and recovery.
- write_ahead_logging (d3): A protocol requiring log records be flushed to durable storage before the corresponding data changes are applied; ensures durability and atomicity.
- aborted_state (d4): The terminal transaction_state after rollback completes; all acquired locks are released and the transaction cannot be restarted automatically.
- committed (d4): The terminal transaction_state after durable persistence of all changes; locks are released per locking_protocol rules.
from deep_database_transaction
- statement (d1): A single SQL operation within a transaction; atomicity requires that each statement either fully completes its effect or fully reverts before the next statement begins.
- all_or_nothing (d3): The conceptual guarantee that a transaction executes as an indivisible unit: either every operation succeeds or no operation has any effect.
- partial_state_prevention (d4): The enforcement mechanism ensuring that if a transaction fails at any point before transaction_boundary, no tuple modifications leak into committed_data; achieved by deferring all visible effects until commit.
- before_image (d4): The committed database state of a row immediately before a transaction modifies it; recorded in the undo_log so the modification can be undone if the transaction rolls back.
- compensation_action (d4): A corrective operation executed when forward undo via undo_log is impossible; used in distributed systems where original transaction steps cannot be directly reversed, preserving atomicity through logically equivalent alternatives.
- transaction_boundary (d5): The demarcation point between consecutive transaction executions defining the scope over which atomicity applies; all effects within are committed or none are, with no partial visibility across the boundary.
from deep_isolation_level
- committed_data (d1): database state resulting from successfully completed transactions; constitutes the visible universe for read_committed queries
- transaction_read (d2): The act of a transaction executing a read operation; at read_uncommitted this read may return uncommitted_change from concurrent transactions.
- uncommitted_change (d2): A modification to database state made by a transaction that has not yet committed; visible to other transactions at read_uncommitted.
- observation_window (d3): The temporal scope during which a reading transaction may see uncommitted changes from other transactions, bounded by those transactions' commit operations.
CONSUMERS (what needs this)
isolation_level
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.)
