feat(txn)!: DB_TXN_SNAPSHOT is now serializable snapshot isolation (SSI); remove DB_TXN_SNAPSHOT_SAFE - #133
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BREAKING (ABI): DB_TXN_SNAPSHOT now provides serializable snapshot isolation (SSI) -- snapshot isolation plus Cahill serializable conflict detection -- and the separate DB_TXN_SNAPSHOT_SAFE flag (0x800) is REMOVED. There is no longer a plain, non-serializable SI mode via the public API: every snapshot transaction gets SSI and may be aborted with DB_SNAPSHOT_UNSAFE / DB_SNAPSHOT_CONFLICT, and cannot be prepared for two-phase commit. This drops the awkward _SAFE flag name in favor of the natural DB_TXN_SNAPSHOT, at the cost of a deliberate ABI break (the maintainer accepted this). - txn.c: DB_TXN_SNAPSHOT (and the env-wide DB_ENV_TXN_SNAPSHOT) now set both the internal TXN_SNAPSHOT substrate and TXN_SNAPSHOT_SAFE (SSI) states; removed DB_TXN_SNAPSHOT_SAFE from the txn_begin OK_FLAGS mask; prepare() rejection message updated to name DB_TXN_SNAPSHOT. - dist/api_flags + regenerated src/dbinc_auto/api_flags.in + build_windows/db.h: DB_TXN_SNAPSHOT_SAFE definition removed; its 0x800 bit is freed. - db.in: internal TXN_SNAPSHOT comment clarified (substrate, always with SSI). - lang/tcl: -snapshot_safe kept as a compat alias for -snapshot (both now SSI) so existing SSI tests keep working unchanged. The internal TXN_SNAPSHOT_SAFE state and all SSI machinery (SIREAD markers, the lock.c GC, db_meta.c conflict recording) are unchanged. Verified: builds clean; ssi001-009, txn001/003, test001 btree/hash all pass.
Follow the DB_TXN_SNAPSHOT_SAFE removal through the rest of the tree: - docs_src: txnbegin.md merges the two flag entries into one DB_TXN_SNAPSHOT (SSI) description; envset_flags.md, the isolation + transaction-read guides, and program_errorret.md updated; a compatibility note explains the fork's change vs stock Oracle BDB. flag-reconcile.md records the removal. - README.md: the SSI bullet now says DB_TXN_SNAPSHOT is serializable + notes the ABI break. - rfc/0003 (SSI): an Amendment note records the API simplification; INDEX updated. - test/bench/ssi_abort_bench.c: uses DB_TXN_SNAPSHOT (the removed _SAFE flag would not compile); builds clean. TCL -snapshot_safe stays a compat alias (prior commit); the .tcl SSI tests are unchanged and pass. Docs build clean.
Coccinelle convention checksNo new violations. ✅ Resolved since baseline (2) -- update dist/cocci/baseline.txt to lock these in. |
ABI diff vs
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BREAKING (ABI, deliberate).
DB_TXN_SNAPSHOTnow provides serializable snapshot isolation (SSI) — snapshot isolation + Cahill serializable conflict detection — and the separateDB_TXN_SNAPSHOT_SAFEflag (0x800) is removed. This drops the awkward_SAFEflag name in favor of the naturalDB_TXN_SNAPSHOT, at the cost of an ABI break the maintainer accepted.There is no longer a plain, non-serializable SI mode via the public API: every snapshot transaction gets SSI, may be aborted with
DB_SNAPSHOT_UNSAFE/DB_SNAPSHOT_CONFLICT, and cannot be 2PC-prepared.Engine
txn.c:DB_TXN_SNAPSHOT(and env-wideDB_ENV_TXN_SNAPSHOT) now set both the internalTXN_SNAPSHOTsubstrate andTXN_SNAPSHOT_SAFE(SSI) states; removedDB_TXN_SNAPSHOT_SAFEfrom thetxn_beginOK_FLAGS mask;prepare()message updated.dist/api_flags+ regeneratedapi_flags.in+build_windows/db.h: flag definition removed, 0x800 freed.db.in: internalTXN_SNAPSHOTcomment clarified.lang/tcl:-snapshot_safekept as a compat alias for-snapshot(both now SSI) so existing SSI tests run unchanged.TXN_SNAPSHOT_SAFEstate + all SSI machinery (SIREAD markers, lock.c GC, db_meta.c) are unchanged.Docs / RFC / bench
docs_src:txnbegin.mdmerges the two entries into one SSIDB_TXN_SNAPSHOT; isolation/transaction guides,envset_flags,program_errorret, and the flag-reconcile doc updated with a stock-BDB-vs-fork note.README.md, RFC 0003 (Amendment note),INDEX.mdupdated.test/bench/ssi_abort_bench.cusesDB_TXN_SNAPSHOT(builds clean).Verified
Builds clean;
ssi001–ssi009,txn001/003,test001btree/hash all pass; docs build clean; bench builds.