perf(update): flush buffered in-place overwrites per storage page (C6, Fase B) - #379
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…, Fase B) The UPDATE commit path buffered one record per row (B7) and FlushBuffered- Overwrites wrote each with two pwrites (length prefix + payload). ~10K-row UPDATEs were therefore dominated by per-row write syscalls (~88K ops/s on the fair-PK fixed-width table, ~2,75x behind SQLite). The flush now reads the current on-disk content of each touched storage page once, patches the row payloads into the copy, and writes the page once. Payloads that cross a page boundary take the direct per-record path first so later page reads already include them; length prefixes are unchanged (same-length overwrites are the only in-place case). Runs under appendLock at commit; rollback semantics unchanged (buffers still dropped on rollback). Fair-PK harness (--pk, same machine as master, 2 runs each): fixed-width UPDATE ~88K -> ~153-164K ops/s (+75-85%; gap vs SQLite ~1,7x) legacy UPDATE ~53-56K -> ~64-70K ops/s (+20-25%) DELETE within noise. Regression: AscendingUpdateBatch_BatchedPageFlush_AppliesEveryRow_AcrossReopen (2000-row UPDATE batch = one commit with 2000 buffered overwrites; point reads + reopen verify the page read-modify-write flush). Full suite 1765 tests, 0 failed.
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Samenvatting
Buffered in-place UPDATE-overwrites worden per storage-page geflusht (C6, eerste concrete Fase-B-mijlpaal).
De UPDATE-commit deed per rij 2 pwrites (lengte-prefix + payload): bij ~10K-rij UPDATEs domineerden de per-rij write-syscalls (~88K ops/s op de fair-PK fixed-width tabel, ~2,75x achter SQLite). Nu:
FlushBufferedOverwritesleest de on-disk content van elke geraakte storage-page één keer, patcht de rij-payloads in de kopie en schrijft elke page één keer.appendLockbij commit; rollback-semantiek ongewijzigd.Metingen (fair-PK
--pk, zelfde machine als master, 2 runs elk)UPDATE-gap vs SQLite op fixed-width: ~2,75x → ~1,7x.
Validatie
AscendingUpdateBatch_BatchedPageFlush_AppliesEveryRow_AcrossReopen: 2000-row UPDATE-batch (één commit, 2000 buffered overwrites → per-page RMW-flush), point reads + reopen.