- /* XXX: We could be a bit more efficient here if
- * thread_id_query_string is identical to query_string, (then we
- * could get by with just one database search instead of two). */
-
- matched_query_string = talloc_asprintf (ctx, "%s AND (%s)",
- thread_id_query_string,
- query_string);
- if (unlikely (matched_query_string == NULL))
- return NULL;
+ /* Under normal circumstances we need to do two database
+ * queries. One is for the thread itself (thread_id_query_string)
+ * and the second is to determine which messages in that thread
+ * match the original query (matched_query_string).
+ *
+ * But under two circumstances, we use only the
+ * thread_id_query_string:
+ *
+ * 1. If the original query_string *is* just the thread
+ * specification.
+ *
+ * 2. If the original query_string matches all messages ("" or
+ * "*").
+ *
+ * In either of these cases, we can be more efficient by running
+ * just the thread_id query (since we know all messages in the
+ * thread will match the query_string).
+ *
+ * Beyond the performance advantage, in the second case, it's
+ * important to not try to create a concatenated query because our
+ * parser handles "" and "*" as special cases and will not do the
+ * right thing with a query string of "* and thread:<foo>".
+ **/
+ matched_is_subset_of_thread = 1;
+ if (strcmp (query_string, thread_id_query_string) == 0 ||
+ strcmp (query_string, "") == 0 ||
+ strcmp (query_string, "*") == 0)
+ {
+ matched_is_subset_of_thread = 0;
+ }