The FDB client currently limits all transactions to be below 10 MB in size, and it will throw an error at commit time if the transaction is too big. However, some users may want to restrict that value to be even smaller, as large commits (lets say, between 1 MB and 10 MB in size) have a few different performance problems (see #1466). This should be a cheap way to let them do that.

I think this would make sense both as a transaction option and as a database option, where the database option sets the default value, and then transactions created by the database object can override that value if they wish.