Re: Changeset Extraction v7.6.1

On 2014-02-15 17:29:04 -0500, Robert Haas wrote:
> On Fri, Feb 14, 2014 at 4:55 AM, Andres Freund <andres@2ndquadrant.com> wrote:

> +       /*
> +        * XXX: It's impolite to ignore our argument and keep decoding until the
> +        * current position.
> +        */
> 
> Eh, what?

So, the background here is that I was thinking of allowing to specify a
limit for the number of returned rows. For the sql interface that sounds
like a good idea. I am just not so sure anymore that allowing to specify
a LSN as a limit is sufficient. Maybe simply allow to limit the number
of changes and check everytime a transaction has been replayed?

It's all trivial codewise, I am just wondering about the interface most
users would want.

> +        * We misuse the original meaning of SnapshotData's xip and
> subxip fields
> +        * to make the more fitting for our needs.
> [...]
> +        * XXX: Do we want extra fields instead of misusing existing
> ones instead?
> 
> If we're going to do this, then it surely needs to be documented in
> snapshot.h.  On the second question, you're not the first hacker to
> want to abuse the meanings of the existing fields; SnapshotDirty
> already does it.  It's tempting to think we need a more principled
> approach to this, like what we've done with Node i.e. typedef enum ...
> SnapshotType; and then a separate struct definition for each kind, all
> beginning with SnapshotType type.

Hm, essentially that's what the ->satisfies pointer already is, right?

There's already documentation of the extra fields in snapbuild, but I
understand you'd rather have them moved?

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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