sszuev commented on issue #2195:
URL: https://github.com/apache/jena/issues/2195#issuecomment-1891974098
> `GraphTxn` is intended to provide auto-commit style semantics for
`Graph`'s. However there was a bug in the `GraphTxn` implementation in the
4.10.0 release (#2086) where it incorrectly determined the current transaction
state and wasn't always creating a transaction when necessary (and conversely
would try to incorrectly create a transaction when unnecessary)
>
> So the behaviour you are seeing with 5.0.0-SNAPSHOT is the correct
expected behaviour
>
> Creating the iterator starts a read transaction that isn't committed until
you explicitly `close()` the iterator. Trying to do a `g.add()` tries to start
a write transaction but it can't because the read transaction is still in
progress.
>
> If you plan to use `GraphTxn` seriously then you should explicitly manage
the transactions to get the transaction boundaries appropriate to your
application.
additional note about the original issue. the following test also works in <
5.0.0-SNAPSHOT.
So, the easiest fix to add `close` in terminal operations (such as `toList`)
won't help.
```
Node x = NodeFactory.createURI("X");
Node q = NodeFactory.createURI("Q");
GraphTxn g = new GraphTxn();
g.add(Triple.create(x, q, q));
ExtendedIterator<Triple> it = g.find(Triple.create(x, Node.ANY, Node.ANY));
it.next();
g.add(Triple.create(q, q, x));
```
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