MDEV-31746 Problems with tx_isolation after MDEV-21921

With session tracking on the tx_isolation of importance to
connector frameworks, its important that tracking of tx_isolation
does get informed if a user `set session transaction_isolation=X`
as the alias for tx_isolation.

Rather than just implement this for one variable alias, it
is implemented for all aliases.

To assist with this the key hash of session_tracker is now made up of
the offset, not the sys_var pointer.

The impacts of aliases are:
- If track one variable, its alias changes, you get a tracking
  change on the variable you are monitoring.
- If you track two aliased variables of each other, changing
  a variable will have a tracking events for only one of them.

Aliases of Sys_var_bit are not implemented, because we don't
have them, so would've been no way to verify that the new code works.

Post-Review edits by Sergei Golubchik <serg@mariadb.com>

mysql-test/main/mysqltest_tracking_info.result

@@ -91,3 +91,138 @@ SET GLOBAL event_scheduler=default;
 # MDEV-16470 - Session user variables tracker
 #
 # End of 10.5 tests
+#
+# MDEV-31746 Problems with tx_isolation after MDEV-21921
+#
+# tracking info on
+SET session_track_system_variables='max_insert_delayed_threads';
+SET max_delayed_threads=0;
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- max_insert_delayed_threads
+-- 0
+
+SET @@max_delayed_threads=0;
+SET SESSION max_delayed_threads=0;
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- max_insert_delayed_threads
+-- 0
+
+SET session_track_system_variables='max_delayed_threads';
+SET max_insert_delayed_threads=@@global.max_delayed_threads;
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- max_delayed_threads
+-- 20
+
+SET session_track_system_variables='tx_isolation';
+SET @@session.tx_isolation='READ-COMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-COMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-UNCOMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION transaction_isolation='REPEATABLE-READ';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- REPEATABLE-READ
+
+Track 2, get 2
+SET session_track_system_variables='tx_isolation,transaction_isolation';
+select @@session_track_system_variables;
+@@session_track_system_variables
+tx_isolation
+SET @@session.tx_isolation='READ-COMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-COMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-UNCOMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION transaction_isolation='REPEATABLE-READ';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- REPEATABLE-READ
+
+SET session_track_system_variables='transaction_isolation';
+SET @@session.tx_isolation='READ-COMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- transaction_isolation
+-- READ-COMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- transaction_isolation
+-- READ-UNCOMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION transaction_isolation='REPEATABLE-READ';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- transaction_isolation
+-- REPEATABLE-READ
+
+SET session_track_system_variables='tx_isolation,transaction_isolation,tx_isolation';
+SELECT @@session_track_system_variables;
+@@session_track_system_variables
+tx_isolation
+SET @@session.tx_isolation='READ-COMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-COMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-UNCOMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION transaction_isolation='REPEATABLE-READ';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- REPEATABLE-READ
+
+accumulate as we encounter duplicates
+SET session_track_system_variables='*';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- session_track_system_variables
+-- *
+
+SET @@session.tx_isolation='READ-COMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-COMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- READ-UNCOMMITTED
+
+Warnings:
+Warning	1287	'@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
+SET SESSION transaction_isolation='REPEATABLE-READ';
+-- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
+-- tx_isolation
+-- REPEATABLE-READ
+
+# End of 11.1 tests

mysql-test/main/mysqltest_tracking_info.test

@@ -123,3 +123,59 @@ SET GLOBAL event_scheduler=default;
 #SET @inserted_value=REPEAT(1,16777180);  # Only crashes when >=16777180 (max = 16777216)
 
 --echo # End of 10.5 tests
+
+--echo #
+--echo # MDEV-31746 Problems with tx_isolation after MDEV-21921
+--echo #
+
+--echo # tracking info on
+
+--enable_session_track_info
+
+SET session_track_system_variables='max_insert_delayed_threads';
+SET max_delayed_threads=0;
+SET @@max_delayed_threads=0;
+SET SESSION max_delayed_threads=0;
+
+SET session_track_system_variables='max_delayed_threads';
+SET max_insert_delayed_threads=@@global.max_delayed_threads;
+
+SET session_track_system_variables='tx_isolation';
+
+SET @@session.tx_isolation='READ-COMMITTED';
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+SET SESSION transaction_isolation='REPEATABLE-READ';
+
+--echo Track 2, get 2
+SET session_track_system_variables='tx_isolation,transaction_isolation';
+select @@session_track_system_variables;
+
+SET @@session.tx_isolation='READ-COMMITTED';
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+SET SESSION transaction_isolation='REPEATABLE-READ';
+
+SET session_track_system_variables='transaction_isolation';
+
+SET @@session.tx_isolation='READ-COMMITTED';
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+SET SESSION transaction_isolation='REPEATABLE-READ';
+
+SET session_track_system_variables='tx_isolation,transaction_isolation,tx_isolation';
+
+SELECT @@session_track_system_variables;
+
+SET @@session.tx_isolation='READ-COMMITTED';
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+SET SESSION transaction_isolation='REPEATABLE-READ';
+
+--echo accumulate as we encounter duplicates
+SET session_track_system_variables='*';
+
+SET @@session.tx_isolation='READ-COMMITTED';
+SET SESSION tx_isolation='READ-UNCOMMITTED';
+SET SESSION transaction_isolation='REPEATABLE-READ';
+# TEST GAP, there are no aliases of Sys_var_bit variables, implemented but
+# no tests yet.
+--disable_session_track_info
+
+--echo # End of 11.1 tests

sql/session_tracker.cc

@@ -60,6 +60,16 @@ void Session_sysvars_tracker::vars_list::copy(vars_list* from, THD *thd)
   from->init();
 }
 
+Session_sysvars_tracker::
+sysvar_node_st *Session_sysvars_tracker::vars_list::search(const sys_var *svar)
+{
+  return reinterpret_cast<sysvar_node_st*>(
+           my_hash_search(&m_registered_sysvars,
+                         reinterpret_cast<const uchar*>(&svar->offset),
+                         sizeof(svar->offset)));
+}
+
+
 /**
   Inserts the variable to be tracked into m_registered_sysvars hash.
 
@@ -559,8 +569,9 @@ uchar *Session_sysvars_tracker::sysvars_get_key(const char *entry,
                                                 size_t *length,
                                                 my_bool not_used __attribute__((unused)))
 {
-  *length= sizeof(sys_var *);
-  return (uchar *) &(((sysvar_node_st *) entry)->m_svar);
+  auto key=&(((sysvar_node_st *) entry)->m_svar->offset);
+  *length= sizeof(*key);
+  return (uchar *) key;
 }
 
 

sql/session_tracker.h

@@ -154,14 +154,7 @@ class Session_sysvars_tracker: public State_tracker
       my_hash_free(&m_registered_sysvars);
     }
 
-    sysvar_node_st *search(const sys_var *svar)
-    {
-      return reinterpret_cast<sysvar_node_st*>(
-               my_hash_search(&m_registered_sysvars,
-                             reinterpret_cast<const uchar*>(&svar),
-                             sizeof(sys_var*)));
-    }
-
+    sysvar_node_st *search(const sys_var *svar);
     sysvar_node_st *at(ulong i)
     {
       DBUG_ASSERT(i < m_registered_sysvars.records);