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/storage/heap/ha_heap.h b/storage/heap/ha_heap.h
index 3a7e0060a05..c765e8e2f62 100644
--- a/storage/heap/ha_heap.h
+++ b/storage/heap/ha_heap.h
@@ -51,7 +51,7 @@ public:
             HA_BINLOG_ROW_CAPABLE | HA_BINLOG_STMT_CAPABLE |
             HA_CAN_SQL_HANDLER | HA_CAN_ONLINE_BACKUPS |
             HA_REC_NOT_IN_SEQ | HA_CAN_INSERT_DELAYED | HA_NO_TRANSACTIONS |
-            HA_HAS_RECORDS | HA_STATS_RECORDS_IS_EXACT);
+            HA_HAS_RECORDS | HA_STATS_RECORDS_IS_EXACT | HA_CAN_HASH_KEYS);
   }
   ulong index_flags(uint inx, uint part, bool all_parts) const
   {