How does SQLite handle concurrent writes?

SQLite allows many simultaneous readers, but only ever one writer at a time for a given database file — there's no concept of row-level or table-level locking granularity the way a full client-server database offers; the whole database file is the unit of write locking.

flowchart LR
    A[Multiple readers] -->|can proceed concurrently| B[Database file]
    C[One writer] -->|exclusive access during write| B
    D[Second writer] -->|must wait| C

In the default rollback journal mode, a writer briefly blocks new readers too during the actual commit; in WAL mode, readers can continue concurrently with the single active writer, though a second writer still has to wait its turn. This single-writer model is perfectly adequate for typical embedded, single-application use, but is the central reason SQLite isn't a good fit for applications with many independent processes all needing to write heavily and simultaneously.

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