MDEV-19713 Remove big_tables system variable

mark big_tables deprecated, the server can put temp tables on disk
as needed avoiding "table full" errors.

in case someone would really need to force a tmp table to be created
on disk from the start and for testing allow tmp_memory_table_size
to be set to 0.

fix tests to use that instead (and add a test that it actually
works).

make sure in-memory TREE size limit is never 0 (it's [ab]using
tmp_memory_table_size at the moment)

remove few sys_vars.*_basic tests

1 files changed, 4 insertions, 4 deletions

diff --git a/mysql-test/main/select.test b/mysql-test/main/select.test
index 43984810c66..22baccc625c 100644
--- a/mysql-test/main/select.test
+++ b/mysql-test/main/select.test
@@ -1425,9 +1425,9 @@ drop table tmp;
 
 # big table done
 
-SET BIG_TABLES=1;
+set tmp_memory_table_size=0; # force on-disk tmp table
 select distinct concat(fld3," ",fld3) as namn from t2,t3 where t2.fld1=t3.t2nr order by namn limit 10;
-SET BIG_TABLES=0;
+set tmp_memory_table_size=default;
 select distinct concat(fld3," ",fld3) from t2,t3 where t2.fld1=t3.t2nr order by fld3 limit 10;
 select distinct fld5 from t2 limit 10;
 
@@ -1436,9 +1436,9 @@ select distinct fld5 from t2 limit 10;
 #
 
 select distinct fld3,count(*) from t2 group by companynr,fld3 limit 10;
-SET BIG_TABLES=1; # Force use of MyISAM
+set tmp_memory_table_size=0; # force on-disk tmp table
 select distinct fld3,count(*) from t2 group by companynr,fld3 limit 10;
-SET BIG_TABLES=0;
+set tmp_memory_table_size=default;
 select distinct fld3,repeat("a",length(fld3)),count(*) from t2 group by companynr,fld3 limit 100,10;
 
 #