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It does this by not insisting every commit hit the disk immediately. Instead of updating the main database file right away, it writes changes into side log files first. That is cheaper, so small write transactions finish much faster.

Key idea: keep the database correct even if newest writes are not fully durable yet.

In default mode, commit means "this transaction is recorded in WAL and the database stays valid," not "the browser has definitely flushed this to storage." If the tab crashes or the device loses power, the app may lose the most recent writes, but the database should not come back corrupted.