If the ref is sharded by change ID, the lookup by change ID is
cheaper. This is because now we can list all refs that start with
refs/starred-changes/ plus sharded change ID and looking up refs with
a prefix that end on '/' is optimized in jgit.
Finding all changes that were starred by a user gets more expensive
since now we need to scan the complete refs/starred-changes/ namespace
for this.
The ref format is changed, because we plan to store the users that
have starred a change in the change index, and this means that we need
to look them up each time a change is reindex. If reindexing a change
would require a complete scan over the refs/starred-changes/ namespace
this would result in performance issues.
On the other hand looking up the changes that were starred by a user
can be done via the change index so that we don't need to scan the
refs/starred-changes/ namespace in this case either.
Change-Id: Ib81d46283035ef753d35fbc78684ded9f074bd1f
Signed-off-by: Edwin Kempin <ekempin@google.com>
dfe73dc408