On Mon, 2010-09-20 at 13:17 -0400, Greg Stein wrote:
> On Thu, Sep 16, 2010 at 09:21, Julian Foad <julian.f...@wandisco.com> wrote:
> > Greg Stein wrote:
> >...
> >> Also, please note that I want to expand the presence values
> >> dramatically with this move to NODES. I suggest the following new
> >> values:
> >
> > Can you explain what these would mean, and what are the main advantages?
>
> Primarily: no need to scan to figure out what is going on.
>
> > Some of them look obvious at first glance but the details of
> > child-of-copy etc. are quite complex. If I were to start to guess...
> >
> > For op_depth = 0, we keep using the current set of 'presence' values, as
> > defined for BASE_NODE.
>
> Yes.
>
> > For op_depth > 0, these new values replace the old 'normal',
> > 'base-deleted' and 'not-present' presence values and the old
> > 'moved_here' flag. The old 'excluded' and 'incomplete' are still used.
>
> Yes.
>
> >> * copied [-here]
> >> * moved-here
> >
> > This is a root or a child of a copied/moved sub-tree. 'op_depth'
> > compared with 'local_relpath' depth indicates whether it's the root.
> > 'copyfrom_*' is non-null iff it's the root (?).
>
> Correct on all three parts.
>
> Note: the columns should be named original_* or repos_*, as discussed
> elsewhere.
>
> > Previous encoding: If it's the root, presence==normal + non-null
> > 'copyfrom_*' + 'moved_here'=FALSE/TRUE. If it's a child,
> > presence==normal and scan_addition reveals it's part of a copy/move.
> >
> > Benefits: Avoid scan_addition. Remove the 'moved_here' flag.
>
> Yes, yes.
>
> >> * moved-away (aka deleted)
> >
> > This is a root or a child of a moved-away sub-tree. The new WC
> > location (local relpath) is in 'moved_to' iff it's the root.
>
> Correct. With root detection based on op_depth and local_relpath as
> mentioned above.
>
> > Previous encoding: presence==base-deleted; if it's the root, non-null
> > 'moved_to', else scan_deletion reveals it's a move-away.
>
> The presence could be 'deleted' if you were moving a child of a
> copy/move-here. But note that wc_db does not implement moves, so we
> never got to these encoding details.
>
> > Benefits: Avoid scan_deletion.
>
> Yes.
>
> >> * deleted
> >
> > This node is deleted relative to the layer below. Previous encoding:
> > 'base-deleted' or 'not-present' depending on whether it was a child of a
> > copied subtree.
>
> Correct.
>
> >> * added
> >
> > A simple addition. Previous encoding: presence==normal,
> > copyfrom_*==null, scan_addition reveals it's a simple add. Benefits:
> > avoid scan_addition.
>
> Yes on all.
>
> >...
> > Are my notes close to what you were thinking? (I'm trying to write out
> > the states in a table to be more rigorous about it.)
>
> Spot-on :-D
>
> (part of the reason to expand the set: their semantics become obvious,
> compared to the current encoding)
OK, good, thanks. *More* obvious, yes. (Obvious, not quite: it still
took me half a day of figuring to come up with this concise
description.)
FULL SET OF VALUES
The values listed above cover most of the cases. Next we must consider
how to get a full set of values to represent all possible changes.
The possible changes to an unoccupied path are:
added
copied-here (as root or as child of op)
moved-here (as root or as child of op)
and the possible changes to an occupied path are:
[
delete
moved-away (as root or as child of op)
]
x
[
<no replacement>
added
copied-here (as root or as child of op)
moved-here (as root or as child of op)
]
Are you planning to encode all these combinations as separate values?
That's 11 in total, plus whatever valid combinations that involve
excluded/absent/file-external.
- Julian
> > If this does enable us to eliminate the use of scan_addition and
> > scan_deletion in some cases, even if they (or some simpler versions) are
> > still needed for finding the copyfrom info in other cases, that would be
> > a worthwhile change.
>
> I was originally trying to be minimalist with the presence values, but
> after use/implementation it became obvious that we can simply encode
> operations in the nodes rather than requiring a scan for them.
>
> scan_addition will receive the most benefit since it resolves an "add"
> to an "add/copy-here/move-here". Or in today's implementation add vs
> copy. The scan_deletion never really has to resolve since we don't
> truly implement moved-away. The *concepts* are still in the code
> because I think we need the design and direction rigor.
>
> For the 1.7 release, we should keep scan_* and just change their
> internals. We can rethink other APIs for future releases since these
> are internal to WC. The implementation is generally reading just a row
> or two: read the target row, examine its op_depth, and read the
> operation root's row. We don't have to scan upwards to find the
> operation root.
>
> Cheers,
> -g
