[Opensync-devel] [RFC] Do not clone-demerge-compare, just compare taking capabilities into account

[Henrik /K. <he...@ka...>]

Dear all,

Following up on a previous thread on this list:

>> The current logic in _osync_obj_engine_mapping_find is:
>> Clone (i.e. make a complete copy of) change1. Demerge fields from the
>> clone which are not in caps2.
>> Clone (i.e. make a complete copy of) change2. Demerge fields from the
>> clone which are not in caps1.
>> Compare the two cloned objects.
>> To me this seems unnecessarily complicated and incurs a performance
>>  penalty. Why is this not implemented as a more "intelligent" compare
>>  function, which takes capabilities into account?

> This is pretty new code and more or less just a proof of concept. If you came 
> up with a more efficient solution, let me know. This was the last thing i was 
> working on ... it's not completed.


OK, here is a suggestion:

In  _osync_obj_engine_mapping_find in opensync_obj_engine.c we currently have something which boils down to:

clone_change1 = _osync_obj_engine_clone_and_demerge_change(sinkengine->engine, caps2, change1, error);
clone_change2 = _osync_obj_engine_clone_and_demerge_change(sinkengine->engine, caps1, change2, error);
change1 = clone_change1;
change2 = clone_change2;
tmp_result = osync_change_compare(change1, change2, error);

This could be replaced with

tmp_result = osync_change_compare(change1, change2, caps1, caps2, error);

osync_change_compare and thus osync_data_compare and osync_objformat_compare and maybe other functions would require trivial changes.

It would then boil down to modifying functions like osync_objformat_compare to take capabilities into account (not trivial).

As far as I can see, this would be a far more efficient solution.

The drawback is of course that it needs coding work (=time).

However, as demerge_xmlformat needs heavy work anyway, I think this may be a good time to consider replacing clone-demerge-compare with a compare taking capabilities into account.

What do you all think about this proposal?

/Henrik

PS: This was about demerge. I have not quite figured merge out, maybe somebody more knowledgeable than me could comment on this...