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Journal modes control how Turso handles transaction logging and durability. You can switch between modes at runtime using the PRAGMA journal_mode statement.

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Supported modes

ModeDescriptionStatus
walWrite-Ahead Logging. The default mode for new databases. Provides good concurrency for readers and writers.Stable
mvccMulti-Version Concurrency Control. Enables concurrent transactions with snapshot isolation.Experimental
MVCC mode is experimental and not production ready. Do not use it for critical data. See MVCC limitations below.

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WAL mode

WAL mode is the default for all new Turso databases. In WAL mode:
  • Readers do not block writers and writers do not block readers.
  • A single write transaction is allowed at a time. Concurrent writes fail with SQLITE_BUSY.
  • Transactions use deferred or immediate locking (see Transactions).
Legacy SQLite databases are automatically converted to WAL mode when opened by Turso.

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MVCC mode

MVCC mode enables concurrent transactions with snapshot isolation. Multiple transactions can read and write simultaneously. Write-write conflicts are detected at commit time rather than at lock acquisition time. In MVCC mode, use BEGIN CONCURRENT to take advantage of optimistic concurrency. See Concurrent transactions for full details.

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Querying the current mode

PRAGMA journal_mode;

turso> PRAGMA journal_mode;
┌──────────────┐
│ journal_mode │
├──────────────┤
│ wal          │
└──────────────┘

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Switching modes

Switch to WAL mode: 
PRAGMA journal_mode = wal;
Switch to MVCC mode: 
PRAGMA journal_mode = mvcc;

turso> PRAGMA journal_mode = mvcc;
┌──────────────┐
│ journal_mode │
├──────────────┤
│ mvcc         │
└──────────────┘

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Checkpoint behavior on mode switch

Switching journal modes triggers a checkpoint to ensure all pending changes are persisted before the mode change takes effect. When switching from MVCC back to WAL mode, the MVCC log file is cleared after checkpointing.
If a database is written to using MVCC mode and then opened again without MVCC, the changes are not visible unless the database was first checkpointed.

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Legacy modes

The legacy SQLite journal modes (delete, truncate, persist, memory, off) are recognized by the parser but not supported. Attempting to switch to any of these modes returns an error.

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MVCC limitations

The MVCC implementation is experimental and has the following known limitations:
  • Indexes cannot be created, and databases with indexes cannot be used in MVCC mode.
  • All data is eagerly loaded from disk to memory on first access. Large databases may take a long time to start and will consume significant memory.
  • Only PRAGMA wal_checkpoint(TRUNCATE) is supported, and it blocks both readers and writers.
  • AUTOINCREMENT is not supported. Tables with AUTOINCREMENT cannot be created or inserted into while MVCC is enabled.
  • Many features may not work, may work incorrectly, or may cause a panic.
  • Queries may return incorrect results.
  • Changes written using MVCC mode are not visible when the database is reopened without MVCC, unless the database was checkpointed first.

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