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, 1 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 35b5665d1d0..40517a6f343 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -18316,7 +18316,6 @@ TABLE *Create_tmp_table::start(THD *thd,
   table->copy_blobs= 1;
   table->in_use= thd;
   table->no_rows_with_nulls= param->force_not_null_cols;
-  table->update_handler= NULL;
   table->check_unique_buf= NULL;
 
   table->s= share;