Bug #23046302 COUNT(*) MUCH SLOWER ON 5.7 THAN 5.6

ANALYSIS

This is regression caused due to worklog 6742 which
implemented ha_innobase::records() which always
uses clustered index to get the row count. Previously
optimizer chose secondary index which was smaller in
size of clustered index to scan for rows and resulted in
a quicker scan.

FIX

After discussion it was decided to remove this feature in 5.7.

[#rb14040 Approved by Kevin and Oystein ]

storage/innobase/handler/ha_innodb.cc

@@ -14230,116 +14230,6 @@ ha_innobase::rename_table(
 	DBUG_RETURN(convert_error_code_to_mysql(error, 0, NULL));
 }
 
-/*********************************************************************//**
-Returns the exact number of records that this client can see using this
-handler object.
-@return Error code in case something goes wrong.
-These errors will abort the current query:
-      case HA_ERR_LOCK_DEADLOCK:
-      case HA_ERR_LOCK_TABLE_FULL:
-      case HA_ERR_LOCK_WAIT_TIMEOUT:
-      case HA_ERR_QUERY_INTERRUPTED:
-For other error codes, the server will fall back to counting records. */
-
-#ifdef MYSQL_57_SELECT_COUNT_OPTIMIZATION
-int
-ha_innobase::records(
-/*==================*/
-	ha_rows*			num_rows) /*!< out: number of rows */
-{
-	DBUG_ENTER("ha_innobase::records()");
-
-	dberr_t		ret;
-	ulint		n_rows = 0;	/* Record count in this view */
-
-	update_thd();
-
-	if (dict_table_is_discarded(m_prebuilt->table)) {
-		ib_senderrf(
-			m_user_thd,
-			IB_LOG_LEVEL_ERROR,
-			ER_TABLESPACE_DISCARDED,
-			table->s->table_name.str);
-
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_NO_SUCH_TABLE);
-
-	} else if (m_prebuilt->table->ibd_file_missing) {
-		ib_senderrf(
-			m_user_thd, IB_LOG_LEVEL_ERROR,
-			ER_TABLESPACE_MISSING,
-			table->s->table_name.str);
-
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_TABLESPACE_MISSING);
-
-	} else if (m_prebuilt->table->corrupted) {
-		ib_errf(m_user_thd, IB_LOG_LEVEL_WARN,
-			ER_INNODB_INDEX_CORRUPT,
-			"Table '%s' is corrupt.",
-			table->s->table_name.str);
-
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_INDEX_CORRUPT);
-	}
-
-	TrxInInnoDB	trx_in_innodb(m_prebuilt->trx);
-
-	m_prebuilt->trx->op_info = "counting records";
-
-	dict_index_t*	index = dict_table_get_first_index(m_prebuilt->table);
-
-	ut_ad(dict_index_is_clust(index));
-
-	m_prebuilt->index_usable = row_merge_is_index_usable(
-		m_prebuilt->trx, index);
-
-	if (!m_prebuilt->index_usable) {
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_TABLE_DEF_CHANGED);
-	}
-
-	/* (Re)Build the m_prebuilt->mysql_template if it is null to use
-	the clustered index and just the key, no off-record data. */
-	m_prebuilt->index = index;
-	dtuple_set_n_fields(m_prebuilt->search_tuple, 0);
-	m_prebuilt->read_just_key = 1;
-	build_template(false);
-
-	/* Count the records in the clustered index */
-	ret = row_scan_index_for_mysql(m_prebuilt, index, false, &n_rows);
-	reset_template();
-	switch (ret) {
-	case DB_SUCCESS:
-		break;
-	case DB_DEADLOCK:
-	case DB_LOCK_TABLE_FULL:
-	case DB_LOCK_WAIT_TIMEOUT:
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(convert_error_code_to_mysql(ret, 0, m_user_thd));
-	case DB_INTERRUPTED:
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_QUERY_INTERRUPTED);
-	default:
-		/* No other error besides the three below is returned from
-		row_scan_index_for_mysql(). Make a debug catch. */
-		*num_rows = HA_POS_ERROR;
-		ut_ad(0);
-		DBUG_RETURN(-1);
-	}
-
-	m_prebuilt->trx->op_info = "";
-
-	if (thd_killed(m_user_thd)) {
-		*num_rows = HA_POS_ERROR;
-		DBUG_RETURN(HA_ERR_QUERY_INTERRUPTED);
-	}
-
-	*num_rows= n_rows;
-	DBUG_RETURN(0);
-}
-#endif /* MYSQL_57_SELECT_COUNT_OPTIMIZATION */
-
 /*********************************************************************//**
 Estimates the number of index records in a range.
 @return estimated number of rows */
@@ -15586,7 +15476,7 @@ ha_innobase::check(
 			ret = row_count_rtree_recs(m_prebuilt, &n_rows);
 		} else {
 			ret = row_scan_index_for_mysql(
-				m_prebuilt, index, true, &n_rows);
+				m_prebuilt, index, &n_rows);
 		}
 
 		DBUG_EXECUTE_IF(

storage/innobase/handler/ha_innodb.h

 /*****************************************************************************
 
-Copyright (c) 2000, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2000, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2013, 2017, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
@@ -219,9 +219,6 @@ class ha_innobase: public handler
 
 	ha_rows estimate_rows_upper_bound();
 
-	// JAN: TODO: MySQL 5.7
-	// int records(ha_rows* num_rows);
-
 	void update_create_info(HA_CREATE_INFO* create_info);
 
 	int create(

storage/innobase/handler/ha_innopart.cc

 /*****************************************************************************
 
-Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.
+Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
 Copyright (c) 2016, 2017, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
@@ -3004,41 +3004,6 @@ ha_innopart::truncate()
 	DBUG_RETURN(error);
 }
 
-/** Total number of rows in all used partitions.
-Returns the exact number of records that this client can see using this
-handler object.
-@param[out]	num_rows	Number of rows.
-@return	0 or error number. */
-int
-ha_innopart::records(
-	ha_rows*	num_rows)
-{
-	ha_rows	n_rows;
-	int	err;
-	DBUG_ENTER("ha_innopart::records()");
-
-	*num_rows = 0;
-
-	/* The index scan is probably so expensive, so the overhead
-	of the rest of the function is neglectable for each partition.
-	So no current reason for optimizing this further. */
-
-	for (uint i = m_part_info->get_first_used_partition();
-	     i < m_tot_parts;
-	     i = m_part_info->get_next_used_partition(i)) {
-
-		set_partition(i);
-		err = ha_innobase::records(&n_rows);
-		update_partition(i);
-		if (err != 0) {
-			*num_rows = HA_POS_ERROR;
-			DBUG_RETURN(err);
-		}
-		*num_rows += n_rows;
-	}
-	DBUG_RETURN(0);
-}
-
 /** Estimates the number of index records in a range.
 @param[in]	keynr	Index number.
 @param[in]	min_key	Start key value (or NULL).

storage/innobase/handler/ha_innopart.h

@@ -1221,10 +1221,6 @@ class ha_innopart:
 		uchar*	record,
 		uchar*	pos);
 
-	int
-	records(
-		ha_rows*	num_rows);
-
 	int
 	index_next(
 		uchar*	record)

storage/innobase/include/ha_prototypes.h

@@ -38,7 +38,6 @@ simple headers.
 class THD;
 
 // JAN: TODO missing features:
-#undef MYSQL_57_SELECT_COUNT_OPTIMIZATION
 #undef MYSQL_FT_INIT_EXT
 #undef MYSQL_INNODB_PARTITIONING
 #undef MYSQL_PFS

storage/innobase/include/row0mysql.h

 /*****************************************************************************
 
-Copyright (c) 2000, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2000, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2017, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
@@ -540,9 +540,6 @@ row_scan_index_for_mysql(
 	row_prebuilt_t*		prebuilt,	/*!< in: prebuilt struct
 						in MySQL handle */
 	const dict_index_t*	index,		/*!< in: index */
-	bool			check_keys,	/*!< in: true=check for mis-
-						ordered or duplicate records,
-						false=count the rows only */
 	ulint*			n_rows)		/*!< out: number of entries
 						seen in the consistent read */
 	MY_ATTRIBUTE((warn_unused_result));

storage/innobase/row/row0mysql.cc

 /*****************************************************************************
 
-Copyright (c) 2000, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2000, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2017, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
@@ -5046,9 +5046,6 @@ row_scan_index_for_mysql(
 	row_prebuilt_t*		prebuilt,	/*!< in: prebuilt struct
 						in MySQL handle */
 	const dict_index_t*	index,		/*!< in: index */
-	bool			check_keys,	/*!< in: true=check for mis-
-						ordered or duplicate records,
-						false=count the rows only */
 	ulint*			n_rows)		/*!< out: number of entries
 						seen in the consistent read */
 {
@@ -5115,7 +5112,7 @@ row_scan_index_for_mysql(
 		goto func_exit;
 	default:
 	{
-		const char* doing = check_keys? "CHECK TABLE" : "COUNT(*)";
+		const char* doing = "CHECK TABLE";
 		ib::warn() << doing << " on index " << index->name << " of"
 			" table " << index->table->name << " returned " << ret;
 		/* fall through (this error is ignored by CHECK TABLE) */
@@ -5131,9 +5128,6 @@ row_scan_index_for_mysql(
 
 	*n_rows = *n_rows + 1;
 
-	if (!check_keys) {
-		goto next_rec;
-	}
 	/* else this code is doing handler::check() for CHECK TABLE */
 
 	/* row_search... returns the index record in buf, record origin offset
@@ -5215,7 +5209,6 @@ row_scan_index_for_mysql(
 		}
 	}
 
-next_rec:
 	ret = row_search_for_mysql(
 		buf, PAGE_CUR_G, prebuilt, 0, ROW_SEL_NEXT);