mvcc
Overview of Experimental MVCC feature - snapshot isolation, versioning, limitations
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Quick Installnpxskills add tursodatabase/turso--skill mvccInstructions
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databaseembedded-databasesqlsqlite3webassembly
Overview of Experimental MVCC feature - snapshot isolation, versioning, limitations
npxskills add tursodatabase/turso--skill mvccLoading…
Multi-Version Concurrency Control. Work in progress, not production-ready.
CRITICAL: Ignore MVCC when debugging unless the bug is MVCC-specific.
PRAGMA journal_mode = 'mvcc';
Runtime configuration, not a compile-time feature flag. Per-database setting.
Standard WAL: single version per page, readers see snapshot at read mark time.
MVCC: multiple row versions, snapshot isolation. Each transaction sees consistent snapshot at begin time.
| Aspect | WAL | MVCC |
|---|---|---|
| Write granularity | Every commit writes full pages | Affected rows only |
| Readers/Writers | Don't block each other | Don't block each other |
| Persistence | .db-wal | .db-log (logical log) |
| Isolation | Snapshot (page-level) | Snapshot (row-level) |
Each row version tracks:
begin - timestamp when visibleend - timestamp when deleted/replacedbtree_resident - existed before MVCC enabledDatabase
└─ mv_store: MvStore
├─ rows: SkipMap<RowID, Vec<RowVersion>>
├─ txs: SkipMap<TxID, Transaction>
├─ Storage (.db-log file)
└─ CheckpointStateMachine
Per-connection: mv_tx tracks current MVCC transaction.
Shared: MvStore with lock-free crossbeam_skiplist structures.
core/mvcc/mod.rs - Module overviewcore/mvcc/database/mod.rs - Main implementation (~3000 lines)core/mvcc/cursor.rs - Merged MVCC + B-tree cursorcore/mvcc/persistent_storage/logical_log.rs - Disk formatcore/mvcc/database/checkpoint_state_machine.rs - Checkpoint logicFlushes row versions to B-tree periodically.
PRAGMA mvcc_checkpoint_threshold = <pages>;
Process: acquire lock → begin pager txn → write rows → commit → truncate log → fsync → release.
Not implemented:
Known issues:
# Run MVCC-specific tests
cargo test mvcc
# TCL tests with MVCC
make test-mvcc
Use #[turso_macros::test(mvcc)] attribute for MVCC-enabled tests.
#[turso_macros::test(mvcc)]
fn test_something() {
// runs with MVCC enabled
}
core/mvcc/mod.rs documents data anomalies (dirty reads, lost updates, etc.)
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Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).