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RE: [HACKERS] cursors in LLL

From: "Hiroshi Inoue" <Inoue(at)tpf(dot)co(dot)jp>
To: "Vadim Mikheev" <vadim(at)krs(dot)ru>
Cc: "pgsql-hackers" <pgsql-hackers(at)postgreSQL(dot)org>
Subject: RE: [HACKERS] cursors in LLL
Date: 1998-10-06 03:01:50
Message-ID: 000501bdf0d5$a9b2a780$2801007e@cadzone.tpf.co.jp (view raw or flat)
Thread:
Lists: pgsql-hackers
>
> Hiroshi Inoue wrote:
> >
> > Hi all.
> > I'm looking forward to the appearance of LLL in PostgreSQL 6.5
> and have a
> > question about the sensitivity of cursors in LLL.
> >
> > In LLL cursors are INSENSITIVE as Oracle ?
> >
> > Currently cursors are indeterminate and in some cases they are strangely
> > sensitive(for me).
>
> Do you mean seeing row inserted between fetches ?

Yes and in some cases updated rows can be seen many times.

> Should this be changed ?

Yes,at least the option is necessary that changes can't be seen.

> How is this in Oracle, Informix, Sybase, standards ?
>

So far as I know,in Oracle cursors are fixed(logically) when
they are opened.

> > In LLL the behavior of cursors will be more complicated, if
> changes by other
> > transactions can be seen by fetch statements(especially for
> read committed
> > isolation level).
> >
> > I hope INSENSITIVE cursors to be implemented whose behavior we
> can predict
> > and I think that they can be realized according to proposals for LLL by
> > Vadim.
> >
> > In LLL access methods return snapshot of data as they were in
> _some_ point
> > in time.
> > For read committed mode this moment is the time when statement began.
> > For serializable mode this is the time when current transaction began.
> >
> > For a INSENSITIVE cursor this is the time when it was opened(declared),
>                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This is easy to implement.
> But I'd like to know what standards say about cursor sensitivness...
>

In SQL92,cursors are not necessarily INSENSITIVE and there's the option
INSENSITIVE for DECLARE CURSOR statements.

Thanks.

Hiroshi Inoue
Inoue(at)tpf(dot)co(dot)jp


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