Perf improvement: BeginReadTransaction will not use transactions

[PaulStovell]

The "unit of work" in Nevermore was always a "transaction":

using var transaction = store.BeginTransaction();
var person = transaction.Load<Person>("Persons-1");
person.Name = "Fred";
transaction.Update(person);
transaction.Commit();

Since any unit of work may change data, it made sense to always create a transaction. This means every unit of work would open a connection, then call SqlConnection.BeginTransaction.

Nevermore 12 introduced BeginReadTransaction, which can be used to read data but has no methods for changing it. This was mostly intended for geo-replication scenarios where you are reading from a read-only replica, and want to avoid programming errors.

using var transaction = store.BeginReadTransaction();
var people = transaction.Query<Person>().ToList();

However, it still called BeginTransaction with read-committed isolation level for every call. And since we are by definition only reading data, this isn't necessary.

In Nevermore 12.7 the behavior will change so that BeginReadTransaction no longer calls BeginTransaction - it simply opens the SQL connection without creating a transaction. This shaves some time off the query:

The slightly confusing part is that BeginReadTransaction doesn't actually begin a transaction anymore 😆