Re: [Firebird-devel] Metadata without Commitment

[Alex P. <pe...@in...>]

Jim Starkey wrote:

> I've been exploring ways to make uncommited DDL operations work with 
> SQL integrated into the engine.  I think I have a solution that 
> works.  The basic idea is the transaction object maintains it own list 
> of transation-specific relation objects.  SQL language processing 
> currently calls in CStatement::findRelation to location relation 
> objects.  CStatement::findRelation used to call 
> Database::findRelation.  Now it calls a new 
> Transaction::findRelation.  I thought it rather classical, all in all, 
> so rather than describe it, I'm reproducing it below, comments and all:
>
>    Relation* Transaction::findRelation(tdbb *tdbb, const char*
>    relationName)
>    {
>        Database *database = tra_attachment->att_database;
>        Relation *relation = database->findRelation(tdbb, relationName);
>              if (relation)

And what about 'DROP TABLE/VIEW'? Dropped relation will be found in the 
transaction, which issued this command. May be 2 lists of pending 
relations - new and dropped? And before return check, has not given 
relation got in the second list. Certainly, it will be necessary to add 
relations to this list from drop_relation() code.

>            return relation;
>              for (relation = pendingRelations; relation; relation =
>    relation->rel_next)
>            if (relation->rel_name == relationName)
>                return relation;
>              Connect connection = getConnection();
>        PStatement statement = connection->prepareStatement(
>            "select rdb$relation_name from rdb$relations where
>    rdb$relation_name=?");
>        statement->setString(1, relationName);
>        RSet resultSet = statement->executeQuery();
>              if (resultSet->next())
>            {
>            relation = FB_NEW(*database->dbb_permanent) Relation
>    (database, -1);
>            relation->rel_name = relationName;
>            relation->fetchFields(connection);
>            addPendingRelation (relation);
>            }
>              return relation;
>    }
>
> The lifetime of the relation objects created by Transaction is the 
> life of the transaction.  Temporary relation objects currently contain 
> minimal data, but this can be expanded as required.  Relation objects 
> are current just deleted.  Sometime we'll probably have to cut over to 
> reference counting.
>
>