Do not ignore reload errors in compactHead (#8051)

* Modified unknownRefs to unknownRefs.Load()
Signed-off-by: NGayathriVenkatesh <gayaa2010@gmail.com>

* Modified db.go
Signed-off-by: NGayathriVenkatesh <gayaa2010@gmail.com>

* Revert "Modified unknownRefs to unknownRefs.Load()"

This reverts commit 79caf595fa9b9193878dc0dd9dec17d58851ae42.
Signed-off-by: NGayathriVenkatesh <gayaa2010@gmail.com>

* Made changes to reload error in db.go
Signed-off-by: NGayathriVenkatesh <gayaa2010@gmail.com>

tsdb/db.go

@@ -835,8 +835,11 @@ func (db *DB) compactHead(head *RangeHead) (err error) {
 	runtime.GC()
 
 	if err := db.reload(); err != nil {
-		if err := os.RemoveAll(filepath.Join(db.dir, uid.String())); err != nil {
-			return errors.Wrapf(err, "delete persisted head block after failed db reload:%s", uid)
+		if errRemoveAll := os.RemoveAll(filepath.Join(db.dir, uid.String())); errRemoveAll != nil {
+			var merr tsdb_errors.MultiError
+			merr.Add(errors.Wrap(err, "reload blocks"))
+			merr.Add(errors.Wrapf(errRemoveAll, "delete persisted head block after failed db reload:%s", uid))
+			return merr.Err()
 		}
 		return errors.Wrap(err, "reload blocks")
 	}