Use symbol - SHA index rather than SHA index

Author: bmoscon

arctic/chunkstore/chunkstore.py

@@ -39,8 +39,6 @@ def _ensure_index(self):
 
         self._collection.create_index([('symbol', pymongo.HASHED)],
                                       background=True)
-        self._collection.create_index([('sha', pymongo.HASHED)],
-                                      background=True)
         self._collection.create_index([('symbol', pymongo.ASCENDING),
                                       ('sha', pymongo.ASCENDING)],
                                       unique=True,
@@ -221,7 +219,7 @@ def write(self, symbol, item, chunk_size):
         doc['append_count'] = 0
 
         if previous_shas:
-            mongo_retry(self._collection.delete_many)({'sha': {'$in': list(previous_shas)}})
+            mongo_retry(self._collection.delete_many)({'symbol': symbol, 'sha': {'$in': list(previous_shas)}})
 
         mongo_retry(self._symbols.update_one)({'symbol': symbol},
                                               {'$set': doc},