Topic 5 notes — durability, WAL, crash recovery

Predictions (fill BEFORE running fsync_ladder)

Predicted max commits/s at 1 fsync/commit: ______ Predicted group-commit speedup at batch 64: ______

fsync_ladder results

(paste table from cargo run --release --bin fsync_ladder)

Surprises vs predictions:

WAL design decisions (src/wal.rs)

• Page images vs logical records — chose: ______ because:
• Group-commit trigger (size / time / both): ______
• Why replay needs no LSN-idempotence check here (and when it would):

crash_test log

• Rounds passed: ___/100
• Failures seen while developing (torn tail? lost ack? partial txn?) and the bug behind each:

commit_throughput results

Reading-guide questions

postgres xlog (reading-postgres-xlog.md)

1. Why xl_prev when reading forward:
2. FPI sawtooth formula in (dirty rate, checkpoint interval):
3. Raising NUM_XLOGINSERT_LOCKS — when, and the flush-time cost:

turso WAL (reading-turso-wal.md)

1. Page images vs deltas — two buys, one cost:
2. The failure salts catch that checksums alone miss:
3. My experiment’s format choice + justification:

redis AOF/RDB (reading-redis-aof-rdb.md)

1. everysec loss window + the write-postpone logic:
2. AOF-as-LSM mapping + rewrite write amp:
3. Command-log vs page-image vs logical-record ranking for graph mutations:

ARIES (reading-aries.md)

1. Why CLRs are redo-only (crash-during-undo walkthrough):
2. Nested top action for a B-tree split — why correct AND necessary:
3. My topic-3 B+tree + WAL: steal? force? ⇒ which passes needed:

Steal/force 2×2 (from memory):

Aether (reading-aether.md)

1. Why ELR preserves durability for dependents:
2. The ELR hazard (non-logging escape channel):
3. Consolidation array vs postgres’s 8 insert locks:
4. Which bottleneck my M5 design leaves unfixed, and at what commits/s it bites:

M5 log (capstone)

• WAL + recovery for graph mutations behind the storage trait
• crash_test harness pointed at the graph — rounds: ___/100
• Contrast vs FalkorDB-on-redis: durability window of RDB-only, RDB+AOF everysec, AOF always: