Remove dict_col_t::hash, dict_col_t::table,

dict_sys->col_hash, and DICT_POOL_PER_COL_HASH.  (Bug #20877)

The col->table pointer was only needed for maintaining a hash table of
all defined columns in all tables.  The hash table was only looked up
in dict_index_find_cols().  Removing the col->hash and col->table
pointers reduces the size of a table column by two machine words
(usually 8 or 16 bytes).

dict_col_add_to_cache(), dict_col_reposition_in_cache(),
dict_col_remove_from_cache(): Remove.  These only updated dict_sys->col_hash.

dict_index_find_cols(): Use a linear search instead of the hash table.
The time complexity is affected, but this function is only invoked by
dict_index_add_to_cache(), and we only search the columns of a single
table (typically at most a few dozen) as opposed to all columns of all
tables.

dict/dict0dict.c

@@ -48,8 +48,6 @@ rw_lock_t	dict_operation_lock;	/* table create, drop, etc. reserve
 					creating a table or index object */
 #define DICT_POOL_PER_TABLE_HASH 512	/* buffer pool max size per table
 					hash table fixed size in bytes */
-#define DICT_POOL_PER_COL_HASH	128	/* buffer pool max size per column
-					hash table fixed size in bytes */
 #define DICT_POOL_PER_VARYING	4	/* buffer pool max size per data
 					dictionary varying size in bytes */
 
@@ -129,32 +127,6 @@ innobase_get_charset(
 	void*	mysql_thd);	/* in: MySQL thread handle */
 #endif /* !UNIV_HOTBACKUP */
 
-/**************************************************************************
-Adds a column to the data dictionary hash table. */
-static
-void
-dict_col_add_to_cache(
-/*==================*/
-	dict_table_t*	table,	/* in: table */
-	dict_col_t*	col);	/* in: column */
-/**************************************************************************
-Repositions a column in the data dictionary hash table when the table name
-changes. */
-static
-void
-dict_col_reposition_in_cache(
-/*=========================*/
-	dict_table_t*	table,		/* in: table */
-	dict_col_t*	col,		/* in: column */
-	const char*	new_name);	/* in: new table name */
-/**************************************************************************
-Removes a column from the data dictionary hash table. */
-static
-void
-dict_col_remove_from_cache(
-/*=======================*/
-	dict_table_t*	table,	/* in: table */
-	dict_col_t*	col);	/* in: column */
 /**************************************************************************
 Removes an index from the dictionary cache. */
 static
@@ -174,7 +146,7 @@ dict_index_copy(
 	ulint		start,	/* in: first position to copy */
 	ulint		end);	/* in: last position to copy */
 /***********************************************************************
-Tries to find column names for the index in the column hash table and
+Tries to find column names for the index and
 sets the col field of the index. */
 static
 ibool
@@ -774,9 +746,6 @@ dict_init(void)
 	dict_sys->table_id_hash = hash_create(buf_pool_get_max_size()
 					      / (DICT_POOL_PER_TABLE_HASH
 						 * UNIV_WORD_SIZE));
-	dict_sys->col_hash = hash_create(buf_pool_get_max_size()
-					 / (DICT_POOL_PER_COL_HASH
-					    * UNIV_WORD_SIZE));
 	dict_sys->size = 0;
 
 	UT_LIST_INIT(dict_sys->table_LRU);
@@ -941,11 +910,6 @@ dict_table_add_to_cache(
 		ut_a(table2 == NULL);
 	}
 
-	/* Add the columns to the column hash table */
-	for (i = 0; i < table->n_cols; i++) {
-		dict_col_add_to_cache(table, dict_table_get_nth_col(table, i));
-	}
-
 	/* Add table to hash table of tables */
 	HASH_INSERT(dict_table_t, name_hash, dict_sys->table_hash, fold,
 		    table);
@@ -1013,7 +977,6 @@ dict_table_rename_in_cache(
 	ulint		old_size;
 	char*		old_name;
 	ibool		success;
-	ulint		i;
 
 	ut_ad(table);
 #ifdef UNIV_SYNC_DEBUG
@@ -1060,15 +1023,6 @@ dict_table_rename_in_cache(
 		}
 	}
 
-	/* Reposition the columns in the column hash table; they are hashed
-	according to the pair (table name, column name) */
-
-	for (i = 0; i < table->n_cols; i++) {
-		dict_col_reposition_in_cache(table,
-					     dict_table_get_nth_col(table, i),
-					     new_name);
-	}
-
 	/* Remove table from the hash tables of tables */
 	HASH_DELETE(dict_table_t, name_hash, dict_sys->table_hash,
 		    ut_fold_string(table->name), table);
@@ -1258,7 +1212,6 @@ dict_table_remove_from_cache(
 	dict_foreign_t*	foreign;
 	dict_index_t*	index;
 	ulint		size;
-	ulint		i;
 
 	ut_ad(table);
 #ifdef UNIV_SYNC_DEBUG
@@ -1299,12 +1252,6 @@ dict_table_remove_from_cache(
 		index = UT_LIST_GET_LAST(table->indexes);
 	}
 
-	/* Remove the columns of the table from the cache */
-	for (i = 0; i < table->n_cols; i++) {
-		dict_col_remove_from_cache(table,
-					   dict_table_get_nth_col(table, i));
-	}
-
 	/* Remove table from the hash tables of tables */
 	HASH_DELETE(dict_table_t, name_hash, dict_sys->table_hash,
 		    ut_fold_string(table->name), table);
@@ -1323,92 +1270,6 @@ dict_table_remove_from_cache(
 	dict_mem_table_free(table);
 }
 
-/**************************************************************************
-Adds a column to the data dictionary hash table. */
-static
-void
-dict_col_add_to_cache(
-/*==================*/
-	dict_table_t*	table,	/* in: table */
-	dict_col_t*	col)	/* in: column */
-{
-	ulint	fold;
-
-	ut_ad(table && col);
-#ifdef UNIV_SYNC_DEBUG
-	ut_ad(mutex_own(&(dict_sys->mutex)));
-#endif /* UNIV_SYNC_DEBUG */
-	ut_ad(table->magic_n == DICT_TABLE_MAGIC_N);
-
-	fold = ut_fold_ulint_pair(ut_fold_string(table->name),
-				  ut_fold_string(col->name));
-
-	/* Look for a column with same table name and column name: error */
-	{
-		dict_col_t*	col2;
-		HASH_SEARCH(hash, dict_sys->col_hash, fold, col2,
-			    (ut_strcmp(col->name, col2->name) == 0)
-			    && (ut_strcmp((col2->table)->name, table->name)
-				== 0));
-		ut_a(col2 == NULL);
-	}
-
-	HASH_INSERT(dict_col_t, hash, dict_sys->col_hash, fold, col);
-}
-
-/**************************************************************************
-Removes a column from the data dictionary hash table. */
-static
-void
-dict_col_remove_from_cache(
-/*=======================*/
-	dict_table_t*	table,	/* in: table */
-	dict_col_t*	col)	/* in: column */
-{
-	ulint		fold;
-
-	ut_ad(table && col);
-#ifdef UNIV_SYNC_DEBUG
-	ut_ad(mutex_own(&(dict_sys->mutex)));
-#endif /* UNIV_SYNC_DEBUG */
-	ut_ad(table->magic_n == DICT_TABLE_MAGIC_N);
-
-	fold = ut_fold_ulint_pair(ut_fold_string(table->name),
-				  ut_fold_string(col->name));
-
-	HASH_DELETE(dict_col_t, hash, dict_sys->col_hash, fold, col);
-}
-
-/**************************************************************************
-Repositions a column in the data dictionary hash table when the table name
-changes. */
-static
-void
-dict_col_reposition_in_cache(
-/*=========================*/
-	dict_table_t*	table,		/* in: table */
-	dict_col_t*	col,		/* in: column */
-	const char*	new_name)	/* in: new table name */
-{
-	ulint		fold;
-
-	ut_ad(table && col);
-#ifdef UNIV_SYNC_DEBUG
-	ut_ad(mutex_own(&(dict_sys->mutex)));
-#endif /* UNIV_SYNC_DEBUG */
-	ut_ad(table->magic_n == DICT_TABLE_MAGIC_N);
-
-	fold = ut_fold_ulint_pair(ut_fold_string(table->name),
-				  ut_fold_string(col->name));
-
-	HASH_DELETE(dict_col_t, hash, dict_sys->col_hash, fold, col);
-
-	fold = ut_fold_ulint_pair(ut_fold_string(new_name),
-				  ut_fold_string(col->name));
-
-	HASH_INSERT(dict_col_t, hash, dict_sys->col_hash, fold, col);
-}
-
 /********************************************************************
 If the given column name is reserved for InnoDB system columns, return
 TRUE. */
@@ -1606,7 +1467,7 @@ dict_index_remove_from_cache(
 }
 
 /***********************************************************************
-Tries to find column names for the index in the column hash table and
+Tries to find column names for the index and
 sets the col field of the index. */
 static
 ibool
@@ -1616,9 +1477,6 @@ dict_index_find_cols(
 	dict_table_t*	table,	/* in: table */
 	dict_index_t*	index)	/* in: index */
 {
-	dict_col_t*	col;
-	dict_field_t*	field;
-	ulint		fold;
 	ulint		i;
 
 	ut_ad(table && index);
@@ -1628,21 +1486,19 @@ dict_index_find_cols(
 #endif /* UNIV_SYNC_DEBUG */
 
 	for (i = 0; i < index->n_fields; i++) {
-		field = dict_index_get_nth_field(index, i);
-
-		fold = ut_fold_ulint_pair(ut_fold_string(table->name),
-					  ut_fold_string(field->name));
-
-		HASH_SEARCH(hash, dict_sys->col_hash, fold, col,
-			    (ut_strcmp(col->name, field->name) == 0)
-			    && (ut_strcmp((col->table)->name, table->name)
-				== 0));
-		if (col == NULL) {
+		ulint		j;
+		dict_field_t*	field = dict_index_get_nth_field(index, i);
 
-			return(FALSE);
-		} else {
-			field->col = col;
+		for (j = 0; j < table->n_cols; j++) {
+			dict_col_t*	col = dict_table_get_nth_col(table, j);
+			if (!strcmp(col->name, field->name)) {
+				field->col = col;
+				goto found;
+			}
 		}
+
+		return(FALSE);
+found:		;
 	}
 
 	return(TRUE);

dict/dict0mem.c

@@ -134,7 +134,6 @@ dict_mem_table_add_col(
 
 	col->ind = table->n_def - 1;
 	col->name = mem_heap_strdup(table->heap, name);
-	col->table = table;
 	col->ord_part = 0;
 
 	col->clust_pos = REC_MAX_N_FIELDS;

include/dict0dict.h

@@ -943,7 +943,6 @@ struct dict_sys_struct{
 					on name */
 	hash_table_t*	table_id_hash;	/* hash table of the tables, based
 					on id */
-	hash_table_t*	col_hash;	/* hash table of the columns */
 	UT_LIST_BASE_NODE_T(dict_table_t)
 			table_LRU;	/* LRU list of tables */
 	ulint		size;		/* varying space in bytes occupied

include/dict0mem.h

@@ -121,7 +121,6 @@ dict_mem_foreign_create(void);
 
 /* Data structure for a column in a table */
 struct dict_col_struct{
-	hash_node_t	hash;	/* hash chain node */
 	ulint		ind:10;	/* table column position (they are numbered
 				starting from 0) */
 	ulint		clust_pos:10;/* position of the column in the
@@ -130,7 +129,6 @@ struct dict_col_struct{
 				appears in ordering fields of an index */
 	const char*	name;	/* name */
 	dtype_t		type;	/* data type */
-	dict_table_t*	table;	/* back pointer to table of this column */
 };
 
 /* DICT_MAX_INDEX_COL_LEN is measured in bytes and is the max index column