revision-id: 10c0278bc08f4e1b179dfcaae8fbfc4c4a0f51c1 (mariadb-10.2.3-76-g10c0278bc08)
parent(s): 9ea0b44c5696d9357465625c3fc9b7f57a856009
committer: Oleksandr Byelkin
timestamp: 2017-01-18 10:40:17 +0100
message:

MDEV-11825: Make session variables TRACKING enabled by default

—

What's the effect on the performance?

For query which do not change something (which most of the query) I do not see difference:
I make 100000 SELECT 1 and result definitely do not depend on the variable set:
without variables run: 6924 6483 6509 6731
with the variable: 7001 6533 6283 6615

test suite is (with first 2 lines interchangeable of course)

SET session_track_system_variables="";

SET session_track_system_variables="autocommit,character_set_client,character_set_connection,character_set_results,time_zone";

--disable_query_log

--disable_result_log

let $1= 100000;

while ($1)

{

  SELECT 1;

  dec $1;

}

--enable_query_log

--enable_result_log

other extreme case when each execution leads to change:
the same number of SET names:
without variables run: 4739 4721 4744 4700
with the variable: 5120 5340 4873 5124

in this extreme case difference is 7.5% (but I do not think that it is real scenario)

here is test suite for it:

SET session_track_system_variables="";

SET session_track_system_variables="autocommit,character_set_client,character_set_connection,character_set_results,time_zone";

--disable_query_log

--disable_result_log

let $1= 50000;

while ($1)

{

  SET names utf8;

  SET names latin1;

  dec $1;

}

--enable_query_log

--enable_result_log

ok to push, then