Switch the build logs archiver to a more performant query

Fixes #459

workers/buildlogsarchiver.py

@@ -24,34 +24,34 @@ class ArchiveBuildLogsWorker(Worker):
   def _archive_redis_buildlogs(self):
     """ Archive a single build, choosing a candidate at random. This process must be idempotent to
         avoid needing two-phase commit. """
-    try:
-      # Get a random build to archive
-      to_archive = model.build.archivable_buildlogs_query().order_by(db_random_func()).get()
-      logger.debug('Archiving: %s', to_archive.uuid)
-
-      length, entries = build_logs.get_log_entries(to_archive.uuid, 0)
-      to_encode = {
-        'start': 0,
-        'total': length,
-        'logs': entries,
-      }
-
-      with SpooledTemporaryFile(MEMORY_TEMPFILE_SIZE) as tempfile:
-        with GzipFile('testarchive', fileobj=tempfile) as zipstream:
-          for chunk in StreamingJSONEncoder().iterencode(to_encode):
-            zipstream.write(chunk)
-
-        tempfile.seek(0)
-        log_archive.store_file(tempfile, JSON_MIMETYPE, content_encoding='gzip',
-                               file_id=to_archive.uuid)
-
-      to_archive.logs_archived = True
-      to_archive.save()
-
-      build_logs.expire_log_entries(to_archive.uuid)
-
-    except RepositoryBuild.DoesNotExist:
+    # Get a random build to archive
+    to_archive = model.build.get_archivable_build()
+    if to_archive is None:
       logger.debug('No more builds to archive')
+      return
+
+    logger.debug('Archiving: %s', to_archive.uuid)
+
+    length, entries = build_logs.get_log_entries(to_archive.uuid, 0)
+    to_encode = {
+      'start': 0,
+      'total': length,
+      'logs': entries,
+    }
+
+    with SpooledTemporaryFile(MEMORY_TEMPFILE_SIZE) as tempfile:
+      with GzipFile('testarchive', fileobj=tempfile) as zipstream:
+        for chunk in StreamingJSONEncoder().iterencode(to_encode):
+          zipstream.write(chunk)
+
+      tempfile.seek(0)
+      log_archive.store_file(tempfile, JSON_MIMETYPE, content_encoding='gzip',
+                             file_id=to_archive.uuid)
+
+    to_archive.logs_archived = True
+    to_archive.save()
+
+    build_logs.expire_log_entries(to_archive.uuid)
 
 
 if __name__ == "__main__":