Improve update handler (long unique keys on blobs)

MDEV-21606 Improve update handler (long unique keys on blobs)
MDEV-21470 MyISAM and Aria start_bulk_insert doesn't work with long unique
MDEV-21606 Bug fix for previous version of this code
MDEV-21819 2 Assertion `inited == NONE || update_handler != this'

- Move update_handler from TABLE to handler
- Move out initialization of update handler from ha_write_row() to
  prepare_for_insert()
- Fixed that INSERT DELAYED works with update handler
- Give an error if using long unique with an autoincrement column
- Added handler function to check if table has long unique hash indexes
- Disable write cache in MyISAM and Aria when using update_handler as
  if cache is used, the row will not be inserted until end of statement
  and update_handler would not find conflicting rows.
- Removed not used handler argument from
  check_duplicate_long_entries_update()
- Syntax cleanups
  - Indentation fixes
  - Don't use single character indentifiers for arguments

1 files changed, 0 insertions, 4 deletions

diff --git a/sql/temporary_tables.cc b/sql/temporary_tables.cc
index c675b11741a..46465294893 100644
--- a/sql/temporary_tables.cc
+++ b/sql/temporary_tables.cc
@@ -748,11 +748,7 @@ void THD::mark_tmp_tables_as_free_for_reuse()
     while ((table= tables_it++))
     {
       if ((table->query_id == query_id) && !table->open_by_handler)
-      {
-        if (table->update_handler)
-          table->delete_update_handler();
         mark_tmp_table_as_free_for_reuse(table);
-      }
     }
   }