this makes it significantly easier to tweak the tx isolation test parameters,
and also makes it much easier to run the MVCC version of the test without
manually tweaking code inline to make it work.
introduces default options for the non-mvcc and mvcc test variants.
The test now incorrectly takes a shadow snapshot of the DB state
before it is determined that the connection successfully started
a read transaction.
Fix: take the snapshot after we've verified that the read TX started.
If both of the following are true:
1. All read locks are already held
2. The highest readmark of any read lock is less than the committed max frame
Then we must return Busy to the reader, because otherwise they would begin a
transaction with a stale local max frame, and thus not see some committed
changes.
- Busy errors do not rollback the transaction
- Transaction takes snapshot of DB state after its first successful
access of the DB, not before its first attempt to access the DB
If upgrade from read to write transaction fails, don't roll back the
transaction. Instead restore the transaction into its original state,
which allows deferred transactions that have not read anything to
restart automatically.
Fixes#2984
## Beef
Adds `AddColumn`, `DropColumn`, `RenameColumn`
## Details
- Previously the test was hardcoded to assume there's always 2 named
columns, so changed a bunch of things for this reason
- Still assumes the primary key column is always `id` and is never
renamed or dropped etc.
Closes#2434
