config: set synchronous to NORMAL for writes

- https://www.sqlite.org/wal.html#performance_considerations

Author: pmorris-dev

crates/sqlx-sqlite-conn-mgr/README.md

@@ -142,6 +142,32 @@ queries.
    The operation is idempotent and safe to call across multiple sessions,
    allowing concurrent reads during writes.
 
+   **Synchronous Mode: NORMAL vs FULL**
+
+   When WAL mode is enabled, this library sets `PRAGMA synchronous = NORMAL`
+   instead of `FULL` for the following reasons:
+
+   * **Performance**: `NORMAL` provides significantly better write performance
+     (up to 2-3x faster) by reducing the number of fsync operations. With `FULL`,
+     SQLite syncs after every checkpoint; with `NORMAL`, it syncs only the WAL file.
+
+   * **Safety in WAL mode**: `NORMAL` is safe in WAL mode because:
+      * WAL transactions are atomic and durable at the WAL file level
+      * The database file itself can be checkpointed asynchronously
+      * A crash may corrupt the database file, but the WAL file remains intact
+        and will be used to recover on next open
+      * This is different from rollback journal mode where `NORMAL` could cause
+        corruption
+
+   * **Mobile/Desktop Context**: For typical desktop and mobile applications,
+     `NORMAL` provides the best balance of performance and safety. `FULL` is
+     primarily needed for scenarios with unreliable storage hardware or when
+     power loss can occur mid-fsync operation.
+
+   See [SQLite WAL Performance Considerations][wal-perf] for more details.
+
+   [wal-perf]: https://www.sqlite.org/wal.html#performance_considerations
+
 4. **Exclusive Writes**: The write pool has `max_connections=1`, ensuring
    only one writer can exist at a time. Other callers to
    `acquire_writer()` will block (asynchronously) until the current writer

crates/sqlx-sqlite-conn-mgr/src/database.rs

@@ -242,6 +242,11 @@ impl SqliteDatabase {
             .execute(&mut *conn)
             .await?;
 
+         // https://www.sqlite.org/wal.html#performance_considerations
+         sqlx::query("PRAGMA synchronous = NORMAL")
+            .execute(&mut *conn)
+            .await?;
+
          self.wal_initialized.store(true, Ordering::SeqCst);
       }
 
@@ -563,6 +568,17 @@ mod tests {
          "Journal mode should be WAL after first acquire_writer"
       );
 
+      // Check sync setting
+      let (sync,): (i32,) = sqlx::query_as("PRAGMA synchronous")
+         .fetch_one(&mut *writer)
+         .await
+         .unwrap();
+
+      assert_eq!(
+         sync, 1,
+         "Sync mode should be NORMAL after first acquire_writer"
+      );
+
       drop(writer);
 
       db.remove().await.unwrap();