MDEV-371 Unique Index for long columns

This patch implements engine independent unique hash index.

Usage:- Unique HASH index can be created automatically for blob/varchar/test column whose key
 length > handler->max_key_length()
or it can be explicitly specified.

  Automatic Creation:-
   Create TABLE t1 (a blob unique);
  Explicit Creation:-
   Create TABLE t1 (a int , unique(a) using HASH);

Internal KEY_PART Representations:-
 Long unique key_info will have 2 representations.
 (lets understand this with an example create table t1(a blob, b blob , unique(a, b)); )

 1. User Given Representation:- key_info->key_part array will be similar to what user has defined.
 So in case of example it will have 2 key_parts (a, b)

 2. Storage Engine Representation:- In this case there will be only one key_part and it will point to
 HASH_FIELD. This key_part will be always after user defined key_parts.

 So:- User Given Representation          [a] [b] [hash_key_part]
                  key_info->key_part ----^
  Storage Engine Representation          [a] [b] [hash_key_part]
                  key_info->key_part ------------^

 Table->s->key_info will have User Given Representation, While table->key_info will have Storage Engine
 Representation.Representation can be changed into each other by calling re/setup_keyinfo_hash function.

Working:-

1. So when user specifies HASH_INDEX or key_length is > handler->max_key_length(), In mysql_prepare_create_table
One extra vfield is added (for each long unique key). And key_info->algorithm is set to HA_KEY_ALG_LONG_HASH.

2. In init_from_binary_frm_image values for hash_keypart is set (like fieldnr , field and flags)

3. In parse_vcol_defs, HASH_FIELD->vcol_info is created. Item_func_hash is used with list of Item_fields,
   When Explicit length is given by user then Item_left is used to concatenate Item_field values.

4. In ha_write_row/ha_update_row check_duplicate_long_entry_key is called which will create the hash key from
table->record[0] and then call ha_index_read_map , if we found duplicated hash , we will compare the result
field by field.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/unireg.h b/sql/unireg.h
index 17fa19a339e..20cd4c292a6 100644
--- a/sql/unireg.h
+++ b/sql/unireg.h
@@ -180,7 +180,7 @@ enum extra2_frm_value_type {
 };
 
 enum extra2_field_flags {
-  VERS_OPTIMIZED_UPDATE= 1 << INVISIBLE_MAX_BITS
+  VERS_OPTIMIZED_UPDATE= 1 << INVISIBLE_MAX_BITS,
 };
 
 int rea_create_table(THD *thd, LEX_CUSTRING *frm,