Hello, Following what has been decided on the optimizer call, I'm nearly done with making semi-join optimizations off by default in 5.3. However, some of 5.3's new optimizations are still turned on by default. Here is a list of 5.3 features and flags that control them: index_merge_sort_intersection=off semijoin=off firstmatch=off loosescan=off ^^ just done the above. materialization=off derived_merge=on derived_with_keys=on ^^ Are we sure about this? index_condition_pushdown=on ^^ This needs to be discussed too. partial_match_rowid_merge=on partial_match_table_scan=on ^^ These are still off because materialization is off. subquery_cache=on ^^ Need to discuss this. mrr=on mrr_cost_based=off mrr_sort_keys=on ^^ Need to discuss this. I take we should disable MRR, too (since BKA is disabled anyway?) join_cache_incremental=on join_cache_hashed=on join_cache_bka=on optimize_join_buffer_size=on ^^ These are not really on because default join_cache_level setting prevents any of these from being used. Another question is that we *MUST* have documentation in place if we're making a release with features that are disabled by default. BR Sergey -- Sergey Petrunia, Software Developer Monty Program AB, http://askmonty.org Blog: http://s.petrunia.net/blog