[development] Use revisions to replace previews

[Kevin Reynen]

> That's why it was suggested to automatically delete revisions that
> were used for previews. Not that it would become elegant code, but
> that would at least get rid of the overhead.

It doesn't get rid of the overhead... just the makes the database look
cleaner.  A JOIN happens between node and node_revisions any time the body
of the node is displayed regardless of how many revisions you save.

The suggested solution is to allow for "keep x revisions" setting.   Setting
x to 0 would give users a "clean" database, but it doesn't change the fact
that inserts are happening where they haven't happened before.  Inserting
previews is more overhead than not inserting them, but any single insert or
update is not enough to be concerned about.  There are few people as
concerned about Drupal's performance as David Strauss, so I don't think he's
ever going to recommend a change that slows Drupal down.

David makes the case (pretty compelling IMHO) that most big systems, modern
applications, and operating systems are including revisions by default and
that this change would simplify the Drupal code base.

The discussions about using revisions by default and changing preview to be
a saved revision are really separate discussions.

There is still a difference between preview and save.  You can preview 30
times and decide not to save any of those changes.  All of the changes
wouldn't have to be saved.  In the case of previews, I'm assuming that the
default would be to update the active "preview" revision and not keep every
change.  One of my concern has been orphaned previews.  Not because they
would clutter the db, but because if the exist and only an admin could get
to them it would create an additional support responsibility I don't want.

For me to +1 preview as a revision, the UI has to be self serve and
developers maintaining popular modules that would be impacted have to be on
board.


- Kevin Reynen


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