Re: [HACKERS] DROP TABLE inside transaction block

Tom Lane is working on this, and it should be improved for 6.6.


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> 
> 
> Tom Lane ha scritto:
> 
> > Pursuant to a phone conversation I had with Bruce, I added code this
> > morning to reject DROP TABLE or DROP INDEX inside a transaction block;
> > that is, you can't do BEGIN; DROP TABLE foo; END anymore.  The reason
> > for rejecting this case is that we do the wrong thing if the transaction
> > is later aborted.  Following BEGIN; DROP TABLE foo; ABORT, the system
> > tables will claim that foo is still valid (since the changes to them
> > were never committed) but we've already unlinked foo's physical file,
> > and we can't get it back.  Solution: only allow DROP TABLE outside
> > BEGIN, so that the user can't try to change his mind later.
> >
> > However, on second thought I wonder if this cure is worse than the
> > disease.  Will it be unreasonably hard to drop tables using client
> > interfaces that like to wrap everything in BEGIN/END?  Plugging an
> > obscure hole might not be worth that.
> >
> > A possible compromise is not to error out, but just to issue a NOTICE
> > along the lines of "DROP TABLE is not undoable, so don't even think of
> > trying to abort now..."
> >
> > (Of course, what would be really nice is if it just worked, but I don't
> > see any way to make that happen without major changes.  Simply
> > postponing the unlink to end of transaction isn't workable; consider
> > BEGIN; DROP TABLE foo; CREATE TABLE foo; ...)
> >
> > Any thoughts?  Will there indeed be a problem with JDBC or ODBC if we
> > leave this error check in place?
> >
> >                         regards, tom lane
> >
> > ************
> >
> > ************
> 
> Seems a good solution. I have an old note about this problem.
> What about to reject also the following commands inside transactions?
> 
> 
> * BUGS: There are some commands that doesn't work properly
>                inside transactions. Users should NOT use the following
>               statements inside transactions:
> 
>      - DROP TABLE      -- in case of ROLLBACK only table structure
>                                          will be recovered, data will be
> lost.
>      - CREATE VIEWS    -- the behavior of the backend is unpredictable.
>      - ALTER TABLE     -- the behavior of the backend is unpredictable.
>      - CREATE DATABASE -- in case of ROLLBACK will be removed references
>                           from "pg_database" but directory
> $PGDATA/databasename will not be removed.
> 
> Jos_
> 
> 
> 
> 
> ************
> 
> 


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