MDEV-16470 - Session user variables tracker

Based on contribution by Dapeng Huang.

include/mysql.h.pp

@@ -108,6 +108,7 @@ enum enum_session_state_type
   SESSION_TRACK_GTIDS,
   SESSION_TRACK_TRANSACTION_CHARACTERISTICS,
   SESSION_TRACK_TRANSACTION_STATE,
+  SESSION_TRACK_USER_VARIABLES,
   SESSION_TRACK_always_at_the_end
 };
 extern "C" {

include/mysql_com.h

@@ -601,6 +601,7 @@ enum enum_session_state_type
   SESSION_TRACK_GTIDS,
   SESSION_TRACK_TRANSACTION_CHARACTERISTICS,  /* Transaction chistics */
   SESSION_TRACK_TRANSACTION_STATE,            /* Transaction state */
+  SESSION_TRACK_USER_VARIABLES,
   SESSION_TRACK_always_at_the_end             /* must be last */
 };
 

mysql-test/main/mysqld--help.result

@@ -1117,6 +1117,8 @@ The following specify which files/extra groups are read (specified before remain
  characteristics (isolation level, read only/read
  write,snapshot - but not any work done / data modified
  within the transaction).
+ --session-track-user-variables 
+ Track changes to user variables.
  --show-slave-auth-info 
  Show user and password in SHOW SLAVE HOSTS on this
  master.
@@ -1712,6 +1714,7 @@ session-track-schema TRUE
 session-track-state-change FALSE
 session-track-system-variables autocommit,character_set_client,character_set_connection,character_set_results,time_zone
 session-track-transaction-info OFF
+session-track-user-variables FALSE
 show-slave-auth-info FALSE
 silent-startup FALSE
 skip-grant-tables TRUE

mysql-test/main/mysqltest_tracking_info.result

@@ -29,3 +29,13 @@ SET NAMES 'utf8';
 # tracking info off once
 SET NAMES 'big5';
 SET @@session.session_track_system_variables= default;
+#
+# MDEV-16470 - Session user variables tracker
+#
+SET @@session.session_track_user_variables=1;
+SET @a=1;
+SET @b=NULL;
+SELECT @c:=10;
+@c:=10
+10
+SET @@session.session_track_user_variables=0;

mysql-test/main/mysqltest_tracking_info.test

@@ -23,3 +23,14 @@ SET NAMES 'big5';
 --disable_session_track_info
 
 SET @@session.session_track_system_variables= default;
+
+--echo #
+--echo # MDEV-16470 - Session user variables tracker
+--echo #
+SET @@session.session_track_user_variables=1;
+--enable_session_track_info
+SET @a=1;
+SET @b=NULL;
+SELECT @c:=10;
+--disable_session_track_info
+SET @@session.session_track_user_variables=0;

mysql-test/suite/sys_vars/r/session_track_system_variables_basic.result

@@ -12,19 +12,13 @@ SELECT @@session.session_track_system_variables;
 autocommit,character_set_client,character_set_connection,character_set_results,time_zone
 
 # via INFORMATION_SCHEMA.GLOBAL_VARIABLES
-SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track%' ORDER BY VARIABLE_NAME;
+SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 VARIABLE_NAME	VARIABLE_VALUE
-SESSION_TRACK_SCHEMA	ON
-SESSION_TRACK_STATE_CHANGE	OFF
 SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,time_zone
-SESSION_TRACK_TRANSACTION_INFO	OFF
 # via INFORMATION_SCHEMA.SESSION_VARIABLES
-SELECT * FROM INFORMATION_SCHEMA.SESSION_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track%' ORDER BY VARIABLE_NAME;
+SELECT * FROM INFORMATION_SCHEMA.SESSION_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 VARIABLE_NAME	VARIABLE_VALUE
-SESSION_TRACK_SCHEMA	ON
-SESSION_TRACK_STATE_CHANGE	OFF
 SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,time_zone
-SESSION_TRACK_TRANSACTION_INFO	OFF
 SET @global_saved_tmp =  @@global.session_track_system_variables;
 
 # Altering global variable's value

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -3453,6 +3453,16 @@ NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	OFF,STATE,CHARACTERISTICS
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	SESSION_TRACK_USER_VARIABLES
+VARIABLE_SCOPE	SESSION
+VARIABLE_TYPE	BOOLEAN
+VARIABLE_COMMENT	Track changes to user variables.
+NUMERIC_MIN_VALUE	NULL
+NUMERIC_MAX_VALUE	NULL
+NUMERIC_BLOCK_SIZE	NULL
+ENUM_VALUE_LIST	OFF,ON
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	SKIP_EXTERNAL_LOCKING
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BOOLEAN

mysql-test/suite/sys_vars/t/session_track_system_variables_basic.test

@@ -12,10 +12,10 @@ SELECT @@session.session_track_system_variables;
 --echo
 
 --echo # via INFORMATION_SCHEMA.GLOBAL_VARIABLES
-SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track%' ORDER BY VARIABLE_NAME;
+SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 
 --echo # via INFORMATION_SCHEMA.SESSION_VARIABLES
-SELECT * FROM INFORMATION_SCHEMA.SESSION_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track%' ORDER BY VARIABLE_NAME;
+SELECT * FROM INFORMATION_SCHEMA.SESSION_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 
 # Save the global value to be used to restore the original value.
 SET @global_saved_tmp =  @@global.session_track_system_variables;

sql/item_func.cc

@@ -4671,6 +4671,10 @@ update_hash(user_var_entry *entry, bool set_null, void *ptr, size_t length,
     entry->unsigned_flag= unsigned_arg;
   }
   entry->type=type;
+#ifndef EMBEDDED_LIBRARY
+  THD *thd= current_thd;
+  thd->session_tracker.user_variables.mark_as_changed(thd, entry);
+#endif
   return 0;
 }
 
@@ -4760,7 +4764,7 @@ longlong user_var_entry::val_int(bool *null_value) const
 /** Get the value of a variable as a string. */
 
 String *user_var_entry::val_str(bool *null_value, String *str,
-				uint decimals)
+                                uint decimals) const
 {
   if ((*null_value= (value == 0)))
     return (String*) 0;

sql/session_tracker.cc

@@ -16,7 +16,6 @@
 
 
 #include "sql_plugin.h"
-#include "hash.h"
 #include "table.h"
 #include "rpl_gtid.h"
 #include "sql_class.h"
@@ -1182,6 +1181,38 @@ bool Session_state_change_tracker::store(THD *thd, String *buf)
   return false;
 }
 
+
+bool User_variables_tracker::update(THD *thd, set_var *)
+{
+  m_enabled= thd->variables.session_track_user_variables;
+  return false;
+}
+
+
+bool User_variables_tracker::store(THD *thd, String *buf)
+{
+  for (ulong i= 0; i < m_changed_user_variables.size(); i++)
+  {
+    auto var= m_changed_user_variables.at(i);
+    String value_str;
+    bool null_value;
+
+    var->val_str(&null_value, &value_str, DECIMAL_MAX_SCALE);
+    buf->q_append(static_cast<char>(SESSION_TRACK_USER_VARIABLES));
+    ulonglong length= net_length_size(var->name.length) + var->name.length;
+    if (!null_value)
+      length+= net_length_size(value_str.length()) + value_str.length();
+    buf->q_net_store_length(length);
+    buf->q_net_store_data(reinterpret_cast<const uchar*>(var->name.str),
+                          var->name.length);
+    if (!null_value)
+      buf->q_net_store_data(reinterpret_cast<const uchar*>(value_str.ptr()),
+                            value_str.length());
+  }
+  m_changed_user_variables.clear();
+  return false;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 /**

sql/session_tracker.h

@@ -19,12 +19,14 @@
 
 #include "m_string.h"
 #include "thr_lock.h"
+#include "sql_hset.h"
 
 #ifndef EMBEDDED_LIBRARY
 /* forward declarations */
 class THD;
 class set_var;
 class String;
+class user_var_entry;
 
 
 enum enum_session_tracker
@@ -33,6 +35,7 @@ enum enum_session_tracker
   CURRENT_SCHEMA_TRACKER,                        /* Current schema */
   SESSION_STATE_CHANGE_TRACKER,
   TRANSACTION_INFO_TRACKER,                      /* Transaction state */
+  USER_VARIABLES_TRACKER,
   SESSION_TRACKER_END                            /* must be the last */
 };
 
@@ -387,6 +390,35 @@ class Transaction_state_tracker : public State_tracker
         thd->session_tracker.transaction_info.X; } while(0)
 
 
+/**
+  User_variables_tracker
+
+  This is a tracker class that enables & manages the tracking of user variables.
+*/
+
+class User_variables_tracker: public State_tracker
+{
+  Hash_set<const user_var_entry> m_changed_user_variables;
+public:
+  User_variables_tracker():
+    m_changed_user_variables(&my_charset_bin, 0, 0,
+                             sizeof(const user_var_entry*), 0, 0,
+                             HASH_UNIQUE | (mysqld_server_initialized ?
+                             HASH_THREAD_SPECIFIC : 0)) {}
+  bool update(THD *thd, set_var *var);
+  bool store(THD *thd, String *buf);
+  void mark_as_changed(THD *thd, const user_var_entry *var)
+  {
+    if (is_enabled())
+    {
+      m_changed_user_variables.insert(var);
+      set_changed(thd);
+    }
+  }
+  void deinit() { m_changed_user_variables.~Hash_set(); }
+};
+
+
 /**
   Session_tracker
 
@@ -415,6 +447,7 @@ class Session_tracker
   Session_state_change_tracker state_change;
   Transaction_state_tracker transaction_info;
   Session_sysvars_tracker sysvars;
+  User_variables_tracker user_variables;
 
   Session_tracker()
   {
@@ -422,6 +455,7 @@ class Session_tracker
     m_trackers[CURRENT_SCHEMA_TRACKER]= &current_schema;
     m_trackers[SESSION_STATE_CHANGE_TRACKER]= &state_change;
     m_trackers[TRANSACTION_INFO_TRACKER]= &transaction_info;
+    m_trackers[USER_VARIABLES_TRACKER]= &user_variables;
   }
 
   void enable(THD *thd)

sql/sql_base.cc

@@ -56,7 +56,6 @@
 #include "rpl_filter.h"
 #include "sql_table.h"                          // build_table_filename
 #include "datadict.h"   // dd_frm_is_view()
-#include "sql_hset.h"   // Hash_set
 #include "rpl_rli.h"   // rpl_group_info
 #ifdef  __WIN__
 #include <io.h>

sql/sql_class.cc

@@ -1750,6 +1750,7 @@ THD::~THD()
   /* trick to make happy memory accounting system */
 #ifndef EMBEDDED_LIBRARY
   session_tracker.sysvars.deinit();
+  session_tracker.user_variables.deinit();
 #endif //EMBEDDED_LIBRARY
 
   if (status_var.local_memory_used != 0)

sql/sql_class.h

@@ -766,6 +766,7 @@ typedef struct system_variables
   ulong session_track_transaction_info;
   my_bool session_track_schema;
   my_bool session_track_state_change;
+  my_bool session_track_user_variables;
   my_bool tcp_nodelay;
 
   ulong threadpool_priority;
@@ -6319,7 +6320,7 @@ class user_var_entry
 
   double val_real(bool *null_value);
   longlong val_int(bool *null_value) const;
-  String *val_str(bool *null_value, String *str, uint decimals);
+  String *val_str(bool *null_value, String *str, uint decimals) const;
   my_decimal *val_decimal(bool *null_value, my_decimal *result);
   CHARSET_INFO *charset() const { return m_charset; }
   void set_charset(CHARSET_INFO *cs) { m_charset= cs; }

sql/sql_hset.h

@@ -38,6 +38,13 @@ class Hash_set
     m_hash.get_key= (my_hash_get_key)K;
     m_hash.charset= cs;
   }
+  Hash_set(CHARSET_INFO *charset, ulong default_array_elements,
+           size_t key_offset, size_t key_length, my_hash_get_key get_key,
+           void (*free_element)(void*), uint flags)
+  {
+    my_hash_init(&m_hash, charset, default_array_elements, key_offset,
+                 key_length, get_key, free_element, flags);
+  }
   /**
     Destroy the hash by freeing the buckets table. Does
     not call destructors for the elements.
@@ -58,13 +65,8 @@ class Hash_set
   bool insert(T *value)
   {
     my_hash_init_opt(&m_hash, m_hash.charset, START_SIZE, 0, 0,
-                     m_hash.get_key, 0, MYF(0));
-    size_t key_len;
-    uchar *v= reinterpret_cast<uchar *>(value);
-    const uchar *key= m_hash.get_key(v, &key_len, FALSE);
-    if (find(key, key_len) == NULL)
-      return my_hash_insert(&m_hash, v);
-    return FALSE;
+                     m_hash.get_key, 0, HASH_UNIQUE);
+    return my_hash_insert(&m_hash, reinterpret_cast<const uchar*>(value));
   }
   bool remove(T *value)
   {
@@ -78,6 +80,8 @@ class Hash_set
   bool is_empty() const { return m_hash.records == 0; }
   /** Returns the number of unique elements. */
   size_t size() const { return static_cast<size_t>(m_hash.records); }
+  /** Erases all elements from the container */
+  void clear() { my_hash_reset(&m_hash); }
   const T* at(size_t i) const
   {
     return reinterpret_cast<T*>(my_hash_element(const_cast<HASH*>(&m_hash), i));

sql/sys_vars.cc

@@ -6378,6 +6378,22 @@ static Sys_var_mybool Sys_session_track_state_change(
        ON_CHECK(0),
        ON_UPDATE(update_session_track_state_change));
 
+
+static bool update_session_track_user_variables(sys_var *self, THD *thd,
+                                                enum_var_type type)
+{
+  return thd->session_tracker.user_variables.update(thd, 0);
+}
+
+static Sys_var_mybool Sys_session_track_user_variables(
+       "session_track_user_variables",
+       "Track changes to user variables.",
+       SESSION_VAR(session_track_user_variables),
+       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
+       NO_MUTEX_GUARD, NOT_IN_BINLOG,
+       ON_CHECK(0),
+       ON_UPDATE(update_session_track_user_variables));
+
 #endif //EMBEDDED_LIBRARY
 
 static Sys_var_uint Sys_in_subquery_conversion_threshold(