MDEV-39013: Fix flaky main.tmp_space_usage test

Reading information_schema.session_status with tmp_memory_table_size=0
forces the query's internal temp table to disk, which changes
tmp_space_used as a side effect of reading it. By the time connection
c1 reads the value from processlist, it sees the inflated value.

Fix by temporarily setting tmp_memory_table_size high before the
session_status read, same pattern already used earlier in the test
(lines 72-77) for the same reason.

Signed-off-by: Varun Deep Saini <varun.23bcs10048@ms.sst.scaler.com>

Author: Varun Deep Saini

mysql-test/main/tmp_space_usage.result

@@ -69,6 +69,8 @@ create table t1 (a int primary key, v varchar(256), c int default(0)) engine=inn
 create table t2 (a int primary key, v varchar(256), c int default(0)) engine=innodb;
 begin;
 insert into t1 (a,v) select seq, repeat(char(64+mod(seq,32)),mod(seq,254)+1) from seq_1_to_3000;
+set @@tmp_memory_table_size=1024*1024;
+set @@tmp_memory_table_size=0;
 connection c1;
 # information_schema.process_list.tmp_space_used == status.tmp_space_used
 insert into t2 (a,v) select seq, repeat(char(64+mod(seq,32)),mod(seq,254)+1) from seq_1_to_3000;

mysql-test/main/tmp_space_usage.test

@@ -102,7 +102,11 @@ begin;
 insert into t1 (a,v) select seq, repeat(char(64+mod(seq,32)),mod(seq,254)+1) from seq_1_to_3000;
 
 let $id=`select connection_id()`;
+# Use memory for the session_status query's internal temp table so it
+# does not change tmp_space_used as a side effect of reading it.
+set @@tmp_memory_table_size=1024*1024;
 let $tmp_usage1=`select variable_value from information_schema.session_status where variable_name="tmp_space_used"`;
+set @@tmp_memory_table_size=0;
 
 connection c1;
 --disable_query_log