Re: [Gnumed-devel] Corrupt database

[Karsten Hilbert]

On Sat, Jun 01, 2013 at 08:44:02AM +0200, Jerzy Luszawski wrote:

> > > 2. How to drop a readonly table 
> > 
> > set default_transaction_read_only to off;
> > drop table ...;
> 
> If I understand this option correctly, using it is insecure, as any
> transaction (may be from all over the world) started before resetting
> it to ON becomes read-write.

*started before* ?   I can't believe that to be true.

To my knowledge it affect transactions started *after*
issuing this WITHIN THIS CONNECTION ONLY.

Maybe I am wrong ?

        default_transaction_read_only (boolean)

        A read-only SQL transaction cannot alter non-temporary
        tables. This parameter controls the default read-only
        status of each new transaction. The default is off (
        read/write).

[...] of each NEW transaction [...]

Now, when a new connection is made it will read several
sources to determine the state: postgresql.conf, database
configuration (which is what GNUmed sets at bootstrap and
checks at startup), user configuration. So, new transactions
very likely have it to ON (unless a user stores a different
default for themselves).

All that does not say anything about NEW transactiosn in
EXISTING connections but I am really hard-pressed to believe
that that should be the case because PostgreSQL is coded
extremely conservative.

> That's why I use 
> 
> set session characteristics as transaction READ WRITE ;

Nonetheless, this is the safer option, indeed !

(Because it applies to the one transaction one runs it in ONLY.)

Thanks for pointing that out.

Karsten
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