perf: durable Columnar DELETE in-place via tombstone markers (no flush rewrite) - #367
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…h rewrite) Non-transactional Columnar deletes now write a tombstone marker over the record's 4-byte length prefix (negative slot size) instead of queueing a flush-time full-file rewrite, so DELETE survives a reopen in O(delete). --pk harness DELETE: ~18.6K ops/s -> ~64K (legacy) / ~81K ops/s (fixed-width), back on par with UPDATE. - IStorage.TombstoneRecord (default false) + Storage implementation (read slot size, write -slotSize marker, evict page cache). - Every raw record enumerator/compactor skips negative prefixes: Storage.ReadAllRecords, AppendOnlyEngine.GetAllRecords + CompactTable, Table.Scanning/CRUD/ParallelScan. - CompactTable broke on a negative prefix, which made the ULID-migration compaction (delete+insert then CompactStorage) write an empty file; it now skips tombstones so migration stays correct. - Transactional deletes are NOT tombstoned at delete time (a marker would survive a rollback that restores the row in the PK index); they are physically removed by the post-commit flush/dispose compaction against the current PK, keeping the rollback-safe semantics of #366. - Tombstone space is reclaimed by the tombstone-aware CompactStorage/CompactTable (explicit, auto-compact threshold, ULID migration). CHANGELOG updated.
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This was referenced Sep 3, 2026
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Why
Master #366 made Columnar DELETE durable by compacting at flush/dispose, but the rewrite cost dropped
--pkDELETE to ~18.6K ops/s (0.54s per 10K deletes on a ~100K-row table).This PR makes the durable delete in-place: a tombstone marker is written over the record's 4-byte length prefix (negative slot size), and every raw record enumerator/compactor skips the slot. DELETE survives a reopen in O(delete) — no flush-time rewrite.
Root cause this PR fixes
The earlier tombstone attempt was reverted because the ULID-migration flow (
delete + insert→CompactStorage) produced an empty.dat(rows=1,filelen=0). Cause found:AppendOnlyEngine.CompactTabledidbreakon any non-positive prefix, so the first tombstone stopped the walk and nothing active was rewritten. It now skips negative prefixes like every other enumerator.Rollback safety
A tombstone written before a transaction commits would survive a rollback that restores the row in the PK index. Transactional deletes are therefore not tombstoned at delete time; they are physically removed by the post-commit flush/dispose compaction against the current PK — the rollback-safe semantics of #366. Non-transactional DELETE (the measured hot path) never pays that rewrite.
Measured (
--pkharness, DELETE 10K of ~100K rows)DELETE is again on par with UPDATE (FW UPDATE ~86.7K ops/s). Tombstone space is reclaimed by the tombstone-aware
CompactTable/CompactStorage(explicit, auto-compact threshold, ULID migration).Validation
SharpCoreDB.Testssuite (Debug + Release/CI filter): green (1656 tests, incl.LegacyUlidMigrationTests, ULID, bulk-delete, reopen, fixed-width, transaction suites).Category!=Debug&Category!=Manual&Category!=Performance):SharpCoreDB.Tests,SharpCoreDB.VectorSearch.Tests,SharpCoreDB.EntityFrameworkCore.Tests,SharpCoreDB.Functional.Linq2DB.Tests— all EXIT=0.