dont add to the lookup table if it already exists

backend/onyx/background/celery/tasks/vespa/tasks.py

@@ -897,7 +897,9 @@ def monitor_vespa_sync(self: Task, tenant_id: str | None) -> bool | None:
             # this is just a migration concern and should be unnecessary once
             # lookup tables are rolled out
             for key_bytes in r_replica.scan_iter(count=SCAN_ITER_COUNT_DEFAULT):
-                if is_fence(key_bytes):
+                if is_fence(key_bytes) and not r.sismember(
+                    OnyxRedisConstants.ACTIVE_FENCES, key_bytes
+                ):
                     logger.warning(f"Adding {key_bytes} to the lookup table.")
                     r.sadd(OnyxRedisConstants.ACTIVE_FENCES, key_bytes)
 

backend/onyx/redis/redis_pool.py

@@ -114,6 +114,7 @@ class TenantRedis(redis.Redis):
             "create_lock",
             "startswith",
             "smembers",
+            "sismember",
             "sadd",
             "srem",
             "scard",