Use SQLite in WAL mode, with IMMEDIATE transactions #412
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WAL mode is generally better, and allows concurrent reads to happen concurrently with other reads and writes. It does not allow writes concurrently with writes, though, failing with SQLITE_BUSY if that occurs. SQLite's `busy_timeout` allows retrying on SQLITE_BUSY, but that does not work if a read-only transaction is upgraded to a write transaction, which is what `TransactionBehavior::Deferred` (a.k.a. `BEGIN DEFERRED`) does. `TransactionBehavior::Immediate` always begins a write transaction immediately, fails with SQLITE_BUSY if that is not allowed, and uses the `busy_timeout` logic to try to wait for the running transaction to finish. This includes a unit test, but as the issue is a race condition, the test does not always fail without the fix. However, it reliably passes with the fix, which is really the important bit.
ryneeverett
approved these changes
Jul 11, 2024
Co-authored-by: ryneeverett <ryneeverett@gmail.com>
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WAL mode is generally better, and allows concurrent reads to happen concurrently with other reads and writes. It does not allow writes concurrently with writes, though, failing with SQLITE_BUSY if that occurs.
SQLite's
busy_timeoutallows retrying on SQLITE_BUSY, but that does not work if a read-only transaction is upgraded to a write transaction, which is whatTransactionBehavior::Deferred(a.k.a.BEGIN DEFERRED) does.TransactionBehavior::Immediatealways begins a write transaction immediately, fails with SQLITE_BUSY if that is not allowed, and uses thebusy_timeoutlogic to try to wait for the running transaction to finish.This includes a unit test, but as the issue is a race condition, the test does not always fail without the fix. However, it reliably passes with the fix, which is really the important bit.
This fixes GothenburgBitFactory/taskwarrior#3325.