MDEV-26938 Support descending indexes internally in InnoDB

This is loosely based on the InnoDB changes in
mysql/mysql-server@97fd8b1b6993340b361fa7f85da86a308f0b5e0c
that I had developed in 2015 or 2016.

For each B-tree key field, we will allow a flag ASC/DESC to be associated.
When PRIMARY KEY fields are internally appended to secondary indexes,
the ASC/DESC attribute will be inherited, so that covering index scans
will work as expected.

Note: Until the subsequent commit, the DESC attribute will be ignored
(no HA_REVERSE_SORT flag will be written to .frm files).

dict_field_t::descending: A new flag to denote descending order.

cmp_data(), cmp_dfield_dfield(): Add a new parameter descending.

cmp_dtuple_rec(), cmp_dtuple_rec_with_match(): Add a parameter "index".

dtuple_coll_eq(): Replaces dtuple_coll_cmp().

cmp_dfield_dfield_eq_prefix(): Replaces cmp_dfield_dfield_like_prefix().

dict_index_t::is_btree(): Check whether the index is a regular
B-tree index (not SPATIAL, FULLTEXT, or the ibuf.index,
or a corrupted index.

btr_cur_search_to_nth_level_func(): Only attempt to use
the adaptive hash index if index->is_btree().
This function may also be invoked on ibuf.index, and
cmp_dtuple_rec_with_match_bytes() will no longer work on ibuf.index
because it assumes that the index and record fields exactly match.
The ibuf.index is a special variadic index tree.

Thanks to Thirunarayanan Balathandayuthapani for fixing some bugs:
MDEV-27439, MDEV-27374/MDEV-27445.

1 files changed, 19 insertions, 13 deletions

diff --git a/storage/innobase/include/dict0mem.h b/storage/innobase/include/dict0mem.h
index 744ef5316ef..54e2a99e4bd 100644
--- a/storage/innobase/include/dict0mem.h
+++ b/storage/innobase/include/dict0mem.h
@@ -396,18 +396,7 @@ dict_mem_index_create(
 	ulint		type,		/*!< in: DICT_UNIQUE,
 					DICT_CLUSTERED, ... ORed */
 	ulint		n_fields);	/*!< in: number of fields */
-/**********************************************************************//**
-Adds a field definition to an index. NOTE: does not take a copy
-of the column name if the field is a column. The memory occupied
-by the column name may be released only after publishing the index. */
-void
-dict_mem_index_add_field(
-/*=====================*/
-	dict_index_t*	index,		/*!< in: index */
-	const char*	name,		/*!< in: column name */
-	ulint		prefix_len);	/*!< in: 0 or the column prefix length
-					in a MySQL index like
-					INDEX (textcol(25)) */
+
 /**********************************************************************//**
 Frees an index memory object. */
 void
@@ -886,9 +875,11 @@ struct dict_field_t{
 	unsigned	fixed_len:10;	/*!< 0 or the fixed length of the
 					column if smaller than
 					DICT_ANTELOPE_MAX_INDEX_COL_LEN */
+	/** 1=DESC, 0=ASC */
+	unsigned	descending:1;
 
 	/** Zero-initialize all fields */
-	dict_field_t() : col(NULL), name(NULL), prefix_len(0), fixed_len(0) {}
+	dict_field_t() { memset((void*) this, 0, sizeof *this); }
 
 	/** Check whether two index fields are equivalent.
 	@param[in]	old	the other index field
@@ -1415,6 +1406,21 @@ inline void dict_col_t::detach(const dict_index_t &index)
     reinterpret_cast<dict_v_col_t*>(this)->detach(index);
 }
 
+/** Add a field definition to an index.
+@param index         index
+@param name          pointer to column name
+@param prefix_len    column prefix length, or 0
+@param descending    whether to use descending order */
+inline void dict_mem_index_add_field(dict_index_t *index, const char *name,
+                                     ulint prefix_len, bool descending= false)
+{
+  ut_ad(index->magic_n == DICT_INDEX_MAGIC_N);
+  dict_field_t &field= index->fields[index->n_def++];
+  field.name= name;
+  field.prefix_len= prefix_len & ((1U << 12) - 1);
+  field.descending= descending;
+}
+
 /** The status of online index creation */
 enum online_index_status {
 	/** the index is complete and ready for access */