contest: fetcher: trim the result manifest at 500 entries

NIPA CI has now run for a year, we have generated ~3150 branches.
The size of the each is around 0.5MB. It's not a problem, yet,
but keep the growth in check, trip the manifest at 500 entries.

The result-fetcher does not care about disappearing entries,
all-results.json will shrink accordingly but that's only for
the best.

Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

contest/remote/lib/fetcher.py

@@ -71,6 +71,9 @@ def _result_set(self, branch_name, url):
         if not found:
             old_db.append({'url': url, 'branch': branch_name, 'executor': self.name})
 
+        # Maintain only the last 500 entries
+        old_db = old_db[-500:]
+
         with open(self._results_manifest, "w") as fp:
             json.dump(old_db, fp)