MDEV-6714 mysqldump slow with tables in big databases

mysqldump now attempts to make use of the INFORMATION_SCHEMA tables.
If the table name is not found with a case sensitive search, it
fallbacks to a case insensitive search.

Author: cvicentiu

client/mysqldump.c

@@ -1735,11 +1735,11 @@ static my_bool test_if_special_chars(const char *str)
 } /* test_if_special_chars */
 
 
-
 /*
   quote_name(name, buff, force)
 
-  Quotes char string, taking into account compatible mode
+  Quotes a string, if it requires quoting. To force quoting regardless
+  of the characters within the string, the force flag can be set to true.
 
   Args
 
@@ -1748,8 +1748,8 @@ static my_bool test_if_special_chars(const char *str)
   force                Flag to make it ignore 'test_if_special_chars'
 
   Returns
-
-  buff                 quoted string
+     A pointer to the quoted string, or the original string if nothing has
+     changed.
 
 */
 static char *quote_name(const char *name, char *buff, my_bool force)
@@ -1815,6 +1815,26 @@ static char *quote_for_like(const char *name, char *buff)
   return buff;
 }
 
+static char *quote_for_equal(const char *name, char *buff)
+{
+  char *to= buff;
+  *to++= '\'';
+  while (*name)
+  {
+    if (*name == '\\')
+    {
+      *to++='\\';
+    }
+    if (*name == '\'')
+      *to++= '\\';
+    *to++= *name++;
+  }
+  to[0]= '\'';
+  to[1]= 0;
+  return buff;
+
+}
+
 
 /**
   Quote and print a string.
@@ -3341,8 +3361,10 @@ static int dump_triggers_for_table(char *table_name, char *db_name)
   /* Get list of triggers. */
 
   my_snprintf(query_buff, sizeof(query_buff),
-              "SHOW TRIGGERS LIKE %s",
-              quote_for_like(table_name, name_buff));
+              "SELECT TRIGGER_NAME FROM INFORMATION_SCHEMA.TRIGGERS "
+              "WHERE EVENT_OBJECT_SCHEMA = DATABASE() AND "
+              "EVENT_OBJECT_TABLE = %s",
+              quote_for_equal(table_name, name_buff));
 
   if (mysql_query_with_error_report(mysql, &show_triggers_rs, query_buff))
     goto done;
@@ -4695,29 +4717,37 @@ static my_bool dump_all_views_in_db(char *database)
 
 
 /*
-  get_actual_table_name -- executes a SHOW TABLES LIKE '%s' to get the actual
-  table name from the server for the table name given on the command line.
-  we do this because the table name given on the command line may be a
-  different case (e.g.  T1 vs t1)
-
-  RETURN
-    pointer to the table name
-    0 if error
+  See get_actual_table_name. Used to retrieve the correct table name
+  from the database schema.
 */
-
-static char *get_actual_table_name(const char *old_table_name, MEM_ROOT *root)
+static char *get_actual_table_name_helper(const char *old_table_name,
+                                          my_bool case_sensitive,
+                                          MEM_ROOT *root)
 {
   char *name= 0;
   MYSQL_RES  *table_res;
   MYSQL_ROW  row;
   char query[50 + 2*NAME_LEN];
   char show_name_buff[FN_REFLEN];
-  DBUG_ENTER("get_actual_table_name");
+  DBUG_ENTER("get_actual_table_name_helper");
 
   /* Check memory for quote_for_like() */
   DBUG_ASSERT(2*sizeof(old_table_name) < sizeof(show_name_buff));
-  my_snprintf(query, sizeof(query), "SHOW TABLES LIKE %s",
-              quote_for_like(old_table_name, show_name_buff));
+
+  if (case_sensitive)
+  {
+    DBUG_PRINT("info", ("case sensitive search"));
+    my_snprintf(query, sizeof(query),
+                "SELECT table_name FROM INFORMATION_SCHEMA.TABLES "
+                "WHERE table_schema = DATABASE() AND table_name = %s",
+                quote_for_equal(old_table_name, show_name_buff));
+  }
+  else
+  {
+    DBUG_PRINT("info", ("case insensitive search"));
+    my_snprintf(query, sizeof(query), "SHOW TABLES LIKE %s",
+                quote_for_like(old_table_name, show_name_buff));
+  }
 
   if (mysql_query_with_error_report(mysql, 0, query))
     return NullS;
@@ -4742,13 +4772,68 @@ static char *get_actual_table_name(const char *old_table_name, MEM_ROOT *root)
   DBUG_RETURN(name);
 }
 
+/*
+  get_actual_table_name -- executes a SELECT .. FROM I_S.tables to check
+  if the table name given on the command line matches the one in the database.
+  If the table is not found, it falls back to a slower SHOW TABLES LIKE '%s' to
+  get the actual table name from the server.
+
+  We do this because the table name given on the command line may be a
+  different case (e.g.  T1 vs t1), but checking this takes a long time
+  when there are many tables present.
+
+  RETURN
+    pointer to the table name
+    0 if error
+*/
+
+static char *get_actual_table_name(const char *old_table_name,
+                                   int lower_case_table_names,
+                                   MEM_ROOT *root)
+{
+  char *name= 0;
+  DBUG_ENTER("get_actual_table_name");
+
+  name= get_actual_table_name_helper(old_table_name, TRUE, root);
+  if (!name && !lower_case_table_names)
+    name= get_actual_table_name_helper(old_table_name, FALSE, root);
+  DBUG_RETURN(name);
+}
+
+/*
+  Retrieve the value for the server system variable lower_case_table_names.
+
+  RETURN
+    0 case sensitive.
+    > 0 case insensitive
+*/
+static int get_sys_var_lower_case_table_names()
+{
+  int lower_case_table_names = 0;
+  MYSQL_RES  *table_res;
+  MYSQL_ROW  row;
+  const char *show_var_query = "SHOW VARIABLES LIKE 'lower_case_table_names'";
+  if (mysql_query_with_error_report(mysql, &table_res, show_var_query))
+    return 0; /* In case of error, assume default value of 0 */
+
+  if ((row= mysql_fetch_row(table_res)))
+  {
+    lower_case_table_names= atoi(row[1]);
+    mysql_free_result(table_res);
+  }
+
+  return lower_case_table_names;
+}
+
+
 
 static int dump_selected_tables(char *db, char **table_names, int tables)
 {
   char table_buff[NAME_LEN*2+3];
   DYNAMIC_STRING lock_tables_query;
   MEM_ROOT root;
   char **dump_tables, **pos, **end;
+  int lower_case_table_names;
   DBUG_ENTER("dump_selected_tables");
 
   if (init_dumping(db, init_dumping_tables))
@@ -4758,11 +4843,15 @@ static int dump_selected_tables(char *db, char **table_names, int tables)
   if (!(dump_tables= pos= (char**) alloc_root(&root, tables * sizeof(char *))))
      die(EX_EOM, "alloc_root failure.");
 
+  /* Figure out how to compare table names. */
+  lower_case_table_names = get_sys_var_lower_case_table_names();
+
   init_dynamic_string_checked(&lock_tables_query, "LOCK TABLES ", 256, 1024);
   for (; tables > 0 ; tables-- , table_names++)
   {
     /* the table name passed on commandline may be wrong case */
-    if ((*pos= get_actual_table_name(*table_names, &root)))
+    if ((*pos= get_actual_table_name(*table_names, lower_case_table_names,
+                                     &root)))
     {
       /* Add found table name to lock_tables_query */
       if (lock_tables)
@@ -5369,8 +5458,10 @@ char check_if_ignore_table(const char *table_name, char *table_type)
 
   /* Check memory for quote_for_like() */
   DBUG_ASSERT(2*sizeof(table_name) < sizeof(show_name_buff));
-  my_snprintf(buff, sizeof(buff), "show table status like %s",
-              quote_for_like(table_name, show_name_buff));
+  my_snprintf(buff, sizeof(buff),
+              "SELECT engine FROM INFORMATION_SCHEMA.TABLES "
+              "WHERE table_name = %s",
+              quote_for_equal(table_name, show_name_buff));
   if (mysql_query_with_error_report(mysql, &res, buff))
   {
     if (mysql_errno(mysql) != ER_PARSE_ERROR)
@@ -5388,7 +5479,7 @@ char check_if_ignore_table(const char *table_name, char *table_type)
     mysql_free_result(res);
     DBUG_RETURN(result);                         /* assume table is ok */
   }
-  if (!(row[1]))
+  if (!(row[0]))
     strmake(table_type, "VIEW", NAME_LEN-1);
   else
   {
@@ -5398,7 +5489,7 @@ char check_if_ignore_table(const char *table_name, char *table_type)
       these types, but we do want to use delayed inserts in the dump if
       the table type is _NOT_ one of these types
     */
-    strmake(table_type, row[1], NAME_LEN-1);
+    strmake(table_type, row[0], NAME_LEN-1);
     if (opt_delayed)
     {
       if (strcmp(table_type,"MyISAM") &&