🚀 go-pugleaf

Kovalenko Dmitry wrote:
> Hi
>
>> "Isolation Levels: has nothing to do with whether multiple
>> transactions from a single connection are supported or, if they are,
>> whether the multiple transaction is overlapped or nested.
>
> OK.
> "Active Sessions" - The maximum number of session objects that can be
> active at one time.

Irrelevant to my question.

>
> Property with information about support nested transaction not
> exists. You can analyse return code of StartTransaction:
>
> ITransactionLocal::StartTransaction when there is already an active
> transaction on the session returns XACT_E_XTIONEXISTS.

"XACT_E_XTIONEXISTS
This session can handle only one extant transaction at a time, and there is
presently such a transaction. The session supports a limited number of
nested transactions, and that limit has been reached."

This is good but after the fact. Also from VCL ADO implementation, the
TADOConnection::BeginTrans() does not return the above information.

As you say, there is unfortunately in ADO/OLEDB no way to determine the
level of transaction support prior to calling a transaction. This is very
poor design. Also it appears that there is no way to support overlapped
transactions as opposed to either single transactions or nested transactions
in ADO/OLEDB. Some databases, such as Interbase, support overlapped
transactions and not nested transactions. If I call
TADOConnection::BeginTrans() using Interbase and a transaction already
exists in the connection, does BeginTrans() fail and throw an exception or
does it succeed and return a value of 1 indicating a top-level transaction ?
All in all, MS's documentation on transaction level support is very poor.