Recovery

Checkpoint

A checkpoint records active transactions as recovery metadata.

highlighted = computed this step

Checkpoint

A checkpoint records which transactions were active at that point in the log. This tiny engine keeps checkpoint handling simple and still recomputes the whole recovery result. Note: the active set appears in the log table.

checkpoint record\text{checkpoint record}

Checkpoint record

The compiled log has 1 checkpoint and 1 loser at crash. Note: checkpoint metadata is rendered, not trusted as output.

checkpoints=1,losers=1\text{checkpoints}=1,\quad \text{losers}=1

a simplified redo/undo recovery over a tiny log; ARIES detail (fuzzy checkpoints, CLRs, media recovery) and real durability/fsync are beyond these traces - no product claims.

Checkpoint - CRASH after LSN 6lsntxntypeitembefore->after1T1begin2T1writeA0->53T1commit4T2begin5SYScheckpointactive:T26T2writeB0->9 winners: T1 | losers: T2; redo LSNs: 2; undo LSNs: 6itemvalueA5B0

Summary

Checkpoints are scan metadata, not a substitute for recomputing winners, losers, and recovery. Note: this is simplified redo and undo; ARIES detail, fuzzy checkpoints, CLRs, media recovery, and real fsync durability are deferred.

checkpoint metadata\text{checkpoint metadata}