It can be dangerous for us to run "set read_only" on a production server because it can block in close_cached_tables. More details about the pain this caused at a previous job are at: http://mysqlha.blogspot.com/2008/07/what-exactly-does-flush-tables-with.html Per the code in set_var.cc: /* Perform a 'FLUSH TABLES WITH READ LOCK'. This is a 3 step process: - [1] lock_global_read_lock() - [2] close_cached_tables() - [3] make_global_read_lock_block_commit() [1] prevents new connections from obtaining tables locked for write. [2] waits until all existing connections close their tables. [3] prevents transactions from being committed. */ Can there be a variant that doesn't do #2? My workload doesn't use MyISAM and I don't know if #2 is done because of MyISAM. Calling close_cached_tables seems like a heavy way to force LOCK TABLEs to be unlocked. Any long running queries will cause #2 to block. -- Mark Callaghan mdcallag@gmail.com