Hi, Sergey! Just one question. Why do you need Session_sysvars_tracker::session_track_system_variables if you have THD::system_variables::session_track_system_variables ? On Mar 25, Sergey Vojtovich wrote:

revision-id: a83d6ee812b (mariadb-10.3.12-94-ga83d6ee812b) parent(s): 3c6f17a130b author: Sergey Vojtovich <svoj@mariadb.org> committer: Sergey Vojtovich <svoj@mariadb.org> timestamp: 2019-03-19 23:40:08 +0400 message:

Safe session_track_system_variables snapshot

When enabling system variables tracker, make a copy of global_system_variables.session_track_system_variables under LOCK_global_system_variables. This protects from concurrent variable updates and potential freed memory access, as well as from variable reconstruction (which was previously protected by LOCK_plugin).

We can also use this copy as a session variable pointer, so that we don't have to allocate memory and reconstruct it every time it is referenced.

For this very reason we don't need buffer_length stuff anymore.

As well as don't we need to take LOCK_plugin early in ::enable(). Unified ::parse_var_list() to acquire LOCK_plugin unconditionally. For no apparent reason it wasn't previously acquired for global variable update.

No reason to access session_sysvars_tracker via get_tracker(), so access it directly instead.

Part of MDEV-14984 - regression in connect performance

Regards, Sergei Chief Architect MariaDB and security@mariadb.org