Here's the mission, should you choose to accept it: Answer the question, "What
was the last place that the line of history identified by PATH@REV was copied
from, if any?" in the most efficient way.
Options today:
1. Use svn_ra_get_log() to do a full history crawl of PATH@REV, and
remember the most recent copy operation's source. The cost of
this approach is directly proportional to the number of changes
made to PATH@REV -- the entirety of that item's history.
2. Same #1, but bail out of the log processing as soon as you have
your answer. Cost here is the same with #1, except you reduce
some client-side processing of the logs which predate that most
recent copy (if any). Server cost is the same.
3. Use svn_ra_get_location_segments() to get a summary of the
locations this line of history has occupied over time. The cost
here is completely variable. At best, the server is of 1.5 or
better pedigree with a fully populated node origins cache, and
returns the answer ("no copies") very quickly. At worst there are
no copies in the item's history and the server is pre-1.5 and has
to basically do the same full history crawl that get_logs() does
in order to answer the question. In between are scenarios where
the server can get the location segments fairly quickly but the
client has to then figure out if those location changes were due
to the item itself being copied, or because some parent of it was.
4. An incremental version of one or more of the above, trying to fetch
history in chunks to avoid over-processing. Cost here could be an
improvement, or could not. And code complexity grows.
svn_client__get_copy_source() today goes with option #1. I think, though, that
as we come to rely more on our server for complex information, we need to be
less shy about giving the server the power to answer complex questions. I'd
suggest at *least* an svn_ra_get_copy_source() API, but am open to other ideas
(like a tunneled version of the svn_fs_history* interfaces, or an RA version of
svn_fs_closest_copy(), or *something*).
Major