Fix error on sqlite 3.7

Create the url_cache index on local_media_repository as a background update, so
that we can detect whether we are on sqlite or not and create a partial or
complete index accordingly.

To avoid running the cleanup job before we have built the index, add a bailout
which will defer the cleanup if the bg updates are still running.

Fixes https://github.com/matrix-org/synapse/issues/2572.

1 files changed, 7 insertions, 3 deletions

diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py

index 723f7043f4..dd76e3f7d5 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -348,11 +348,16 @@ class PreviewUrlResource(Resource):
     def _expire_url_cache_data(self):
         """Clean up expired url cache content, media and thumbnails.
         """
-
         # TODO: Delete from backup media store
 
         now = self.clock.time_msec()
 
+        logger.info("Running url preview cache expiry")
+
+        if not self.store.has_completed_background_updates():
+            logger.info("Still running DB updates; skipping expiry")
+            return
+
         # First we delete expired url cache entries
         media_ids = yield self.store.get_expired_url_cache(now)
 
@@ -426,8 +431,7 @@ class PreviewUrlResource(Resource):
 
         yield self.store.delete_url_cache_media(removed_media)
 
-        if removed_media:
-            logger.info("Deleted %d media from url cache", len(removed_media))
+        logger.info("Deleted %d media from url cache", len(removed_media))
 
 
 def decode_and_calc_og(body, media_uri, request_encoding=None):