https://simonwillison.net/2024/Mar/31/optimizing-sqlite-for-servers/ quoting https://kerkour.com/sqlite-for-servers

> By default, SQLite starts transactions in DEFERRED mode: they are considered read only. They are upgraded to a write transaction that requires a database lock in-flight, when query containing a write/update/delete statement is issued.

>

> The problem is that by upgrading a transaction after it has started, SQLite will immediately return a SQLITE_BUSY error without respecting the busy_timeout previously mentioned, if the database is already locked by another connection.

>

> This is why you should start your transactions with BEGIN IMMEDIATE instead of only BEGIN. If the database is locked when the transaction starts, SQLite will respect busy_timeout.

It could be convenient to be able to pass along a busy_timeout value when starting an immediate transaction.