Within notedb each change that is starred by a user is tracked by a
refs/starred-changes/XX/YYYY/ZZZZ ref in the All-Users meta repository
where XX/YYYY is the sharded change ID and ZZZZ is the account ID.
With this storage format finding all users that have starred a
change is cheap because we just need to list all refs that have
refs/starred-changes/XX/YYYY/ as prefix and looking up refs with a
prefix that ends on '/' is optimized in jgit. However to find all
changes that were starred by a user we must scan the complete
refs/starred-changes/ namespace and check which of the refs end with
the account ID. This results in bad performance when there are many
starred changes. Having the users that starred a change stored in the
change index makes this lookup cheap.
Looking up all changes that were starred by a user is needed for
supporting the "is:starred" query operator and for populating the
"starred" field in ChangeInfo.
Change-Id: Iecc9ca8ef133b0d0f86f1471b9ed31be78a43f6c
Signed-off-by: Edwin Kempin <ekempin@google.com>
8be51b8a57