MDEV-22504: Session tracking return incorrectly long traking data

When we move data we should fix buffer string length

mysql-test/r/mysqltest_tracking_info.result

+set @save_session_track_system_variables=@@session_track_system_variables;
 SELECT @@session.character_set_connection;
 @@session.character_set_connection
 latin1
@@ -28,4 +29,19 @@ SET NAMES 'utf8';
 
 # tracking info off once
 SET NAMES 'big5';
-SET @@session.session_track_system_variables= default;
+SET @@session.session_track_system_variables= @save_session_track_system_variables;
+#
+# MDEV-22504: session tracking return incorrectly long traking data
+#
+set @save_optimizer_switch=@@optimizer_switch;
+SET @@session.session_track_system_variables='optimizer_switch';
+set optimizer_switch='index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- optimizer_switch
+-- index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off
+
+Warnings:
+Warning	1681	'engine_condition_pushdown=on' is deprecated and will be removed in a future release
+set @@optimizer_switch=@save_optimizer_switch;
+SET @@session.session_track_system_variables= @save_session_track_system_variables;
+# End of 10.2 tests

mysql-test/t/mysqltest_tracking_info.test

@@ -2,6 +2,9 @@
 --source include/no_protocol.inc
 --source include/not_embedded.inc
 
+
+set @save_session_track_system_variables=@@session_track_system_variables;
+
 SELECT @@session.character_set_connection;
 SET @@session.session_track_system_variables='character_set_connection';
 
@@ -22,4 +25,23 @@ SET NAMES 'utf8';
 SET NAMES 'big5';
 --disable_session_track_info
 
-SET @@session.session_track_system_variables= default;
+SET @@session.session_track_system_variables= @save_session_track_system_variables;
+
+--echo #
+--echo # MDEV-22504: session tracking return incorrectly long traking data
+--echo #
+
+set @save_optimizer_switch=@@optimizer_switch;
+
+SET @@session.session_track_system_variables='optimizer_switch';
+
+--enable_session_track_info
+set optimizer_switch='index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off';
+--disable_session_track_info
+
+set @@optimizer_switch=@save_optimizer_switch;
+
+
+SET @@session.session_track_system_variables= @save_session_track_system_variables;
+
+--echo # End of 10.2 tests

sql/session_tracker.cc

@@ -1698,7 +1698,7 @@ void Session_tracker::store(THD *thd, String *buf)
 
   if ((size= net_length_size(length)) != 1)
   {
-    if (buf->reserve(size - 1, EXTRA_ALLOC))
+    if (buf->reserve(size - 1, 0))
     {
       buf->length(start); // it is safer to have 0-length block in case of error
       return;
@@ -1708,6 +1708,7 @@ void Session_tracker::store(THD *thd, String *buf)
       The 'buf->reserve()' can change the buf->ptr() so we cannot
       calculate the 'data' earlier.
     */
+    buf->length(buf->length() + (size - 1));
     data= (uchar *)(buf->ptr() + start);
     memmove(data + (size - 1), data, length);
   }