commit dfe73dc40810c1e3dfbf07d3459a40f9662b5cfd
author Edwin Kempin <ekempin@google.com> Fri Apr 15 16:34:33 2016 +0200
committer Edwin Kempin <ekempin@google.com> Mon Apr 18 08:39:46 2016 +0200
tree 99a3696b18c738ed6f66af572ce52bf0c803eb25
parent 82d3bfa84c345c366b0483ab3d63af055c2cca0f

Shard refs/starred-changes refs by change ID instead of account ID

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>