Check if the update can proceed on inserts and updatest, fix the overwrite
stuff (again). Probably still wrong, but I'll wait until I can run the
test suite to fix it.
Add support for setting the transaction state on commit/rollback; walk
the session handle and for every data-source cursor, call an underlying
commit or rollback function. I don't see another solution, so I'm doing
this until Michael weighs in: I'm adding private WT_CURSOR methods the
data-source code sets, which is flatly wrong, but the other approaches
seem worse.
Another WT_EXTENSION_API method: the transaction_snapshot_isolation method
returns if snapshot isolation is configured for the current transaction.
Change the WT_EXTENSION_API transaction_id method to return the transaction
ID; it's no more likely to fail than the other transaction methods, and
I don't see them failing in the future either. It's a little dangerous,
but I'd rather keep error handling simple if we can.
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