How to analyze and tune sql queries for better performance vts2016

Copyright © 2016 Oracle and/or its affiliates. All rights reserved. | How to Analyze and Tune MySQL Queries for Better Performance Øystein Grøvlen Senior Principal Software Engineer MySQL Optimizer Team, Oracle March/April, 2016 Please Stand By. This session will begin promptly at the time indicated on the agenda. Thank You.

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Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 3 Program Agenda Cost-based query optimization in MySQL Tools for monitoring, analyzing, and tuning queries Data access and index selection Join optimizer Sorting Influencing the optimizer 1 2 3 4 5 6

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 5 MySQL Optimizer SELECT a, b FROM t1, t2, t3 WHERE t1.a = t2.b AND t2.b = t3.c AND t2.d > 20 AND t2.d < 30; MySQL Server Cost based optimizations Heuristics Cost Model Optimizer Table/index info (data dictionary) Statistics (storage engines) t2 t3 t1 Table scan Range scan Ref access JOIN JOIN

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 6 Cost-based Query Optimization • Assign cost to operations • Assign cost to partial or alternative plans • Search for plan with lowest cost • Cost-based optimizations: General idea Access method Subquery strategyJoin order t2 t3 t1 Table scan Range scan Ref access JOIN JOIN

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 7 Optimizer Cost Model t1 Cost estimate Row estimate Cost Model Cost formulas Access methods Join Subquery Cost constants CPU IO Metadata: - Row and index size - Index information - Uniqueness Statistics: - Table size - Cardinality - Range estimates Cost model configuration Range scan JOIN New in MySQL 5.7

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 8 Cost Model Example Table scan: • IO-cost: #pages in table * IO_BLOCK_READ_COST • CPU cost: #rows * ROW_EVALUATE_COST Range scan (on secondary index): • IO-cost: #rows_in_range * IO_BLOCK_READ_COST • CPU cost: #rows_in_range * ROW_EVALUATE_COST SELECT SUM(o_totalprice) FROM orders WHERE o_orderdate BETWEEN '1994-01-01' AND '1994-12-31';

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 9 Cost Model Example EXPLAIN SELECT SUM(o_totalprice) FROM orders WHERE o_orderdate BETWEEN '1994-01-01' AND '1994-12-31'; EXPLAIN SELECT SUM(o_totalprice) FROM orders WHERE o_orderdate BETWEEN '1994-01-01' AND '1994-06-30'; id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ALL i_o_orderdate NULL NULL NULL 15000000 Using where Id select type table type possible keys key key len ref rows extra 1 SIMPLE orders range i_o_orderdate i_o_orderdate 4 NULL 2235118 Using index condition

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 10 Cost Model Example: Optimizer Trace join_optimization / row_estimation / table : orders / range_analysis "table_scan": { "rows": 15000000, "cost": 3.12e6 } /* table_scan */, "potential_range_indices": [ { "index": "PRIMARY", "usable": false, "cause": "not_applicable" }, { "index": "i_o_orderdate", "usable": true, "key_parts": [ "o_orderDATE", "o_orderkey" ] } ] /* potential_range_indices */, … "analyzing_range_alternatives": { "range_scan_alternatives": [ { "index": "i_o_orderdate", "ranges": [ "1994-01-01 <= o_orderDATE <= 1994-12-31" ], "index_dives_for_eq_ranges": true, "rowid_ordered": false, "using_mrr": false, "index_only": false, "rows": 4489990, "cost": 5.39e6, "chosen": false, "cause": "cost" } ] /* range_scan_alternatives */, … } /* analyzing_range_alternatives */

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 11 Cost Model vs Real World Data in Memory Data on Disk Data on SSD Table scan 6.8 seconds 36 seconds 15 seconds Index scan 5.2 seconds 2.5 hours 30 minutes Measured Execution Times Force Index Scan: SELECT SUM(o_totalprice) FROM orders FORCE INDEX (i_o_orderdate) WHERE o_orderdate BETWEEN '1994-01-01' AND '1994-12-31';

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 12 Performance Schema SELECT event_name, count_read, avg_timer_read/1000000000.0 "Avg Read Time (ms)", sum_number_of_bytes_read "Bytes Read" FROM performance_schema.file_summary_by_event_name WHERE event_name='wait/io/file/innodb/innodb_data_file'; Disk I/O event_name count_read Avg Read Time (ms) Bytes Read wait/io/file/innodb/innodb_data_file 2188853 4.2094 35862167552 event_name count_read Avg Read Time (ms) Bytes Read wait/io/file/innodb/innodb_data_file 115769 0.0342 1896759296 Index Scan Table Scan

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 14 Useful tools • MySQL Enterprise Monitor (MEM), Query Analyzer – Commercial product • Performance schema, MySQL sys schema • EXPLAIN – Tabular EXPLAIN – Structured EXPLAIN (FORMAT=JSON) – Visual EXPLAIN (MySQL Workbench) • Optimizer trace • Slow log • Status variables (SHOW STATUS LIKE 'Sort%')

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 17 Performance Schema • events_statements_history events_statements_history_long – Most recent statements executed • events_statements_summary_by_digest – Summary for similar statements (same statement digest) • file_summary_by_event_name – Interesting event: wait/io/file/innodb/innodb_data_file • table_io_waits_summary_by_table table_io_waits_summary_by_index_usage – Statistics on storage engine access per table and index Some useful tables

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 18 Performance Schema • Tables: events_statements_current (Current statement for each thread) events_statements_history (10 most recent statements per thread) events_statements_history_long (10000 most recent statements) • Columns: THREAD_ID, EVENT_ID, END_EVENT_ID, EVENT_NAME, SOURCE, TIMER_START, TIMER_END, TIMER_WAIT, LOCK_TIME, SQL_TEXT, DIGEST, DIGEST_TEXT, CURRENT_SCHEMA, OBJECT_TYPE, OBJECT_SCHEMA, OBJECT_NAME, OBJECT_INSTANCE_BEGIN, MYSQL_ERRNO, RETURNED_SQLSTATE, MESSAGE_TEXT, ERRORS, WARNINGS, ROWS_AFFECTED, ROWS_SENT, ROWS_EXAMINED, CREATED_TMP_DISK_TABLES, CREATED_TMP_TABLES, SELECT_FULL_JOIN, SELECT_FULL_RANGE_JOIN, SELECT_RANGE, SELECT_RANGE_CHECK, SELECT_SCAN, SORT_MERGE_PASSES, SORT_RANGE, SORT_ROWS, SORT_SCAN, NO_INDEX_USED, NO_GOOD_INDEX_USED, NESTING_EVENT_ID, NESTING_EVENT_TYPE Statement events

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 19 Performance Schema • Normalization of queries to group statements that are similar to be grouped and summarized: SELECT * FROM orders WHERE o_custkey=10 AND o_totalprice>20 SELECT * FROM orders WHERE o_custkey = 20 AND o_totalprice > 100 SELECT * FROM orders WHERE o_custkey = ? AND o_totalprice > ? • events_statements_summary_by_digest DIGEST, DIGEST_TEXT, COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT, SUM_LOCK_TIME, SUM_ERRORS, SUM_WARNINGS, SUM_ROWS_AFFECTED, SUM_ROWS_SENT, SUM_ROWS_EXAMINED, SUM_CREATED_TMP_DISK_TABLES, SUM_CREATED_TMP_TABLES, SUM_SELECT_FULL_JOIN, SUM_SELECT_FULL_RANGE_JOIN, SUM_SELECT_RANGE, SUM_SELECT_RANGE_CHECK, SUM_SELECT_SCAN, SUM_SORT_MERGE_PASSES, SUM_SORT_RANGE, SUM_SORT_ROWS, SUM_SORT_SCAN, SUM_NO_INDEX_USED, SUM_NO_GOOD_INDEX_USED, FIRST_SEEN, LAST_SEEN Statement digest

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 20 MySQL sys Schema • A collection of views, procedures and functions, designed to make reading raw Performance Schema data easier • Implements many common DBA and Developer use cases – File IO usage per user – Which indexes is never used? – Which queries use full table scans? • Examples of very useful functions: – format_time() , format_bytes(), format_statement() • Included with MySQL 5.7 • Bundled with MySQL Workbench

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 21 MySQL sys Schema statement_analysis: Lists a normalized statement view with aggregated statistics, ordered by the total execution time per normalized statement mysql> SELECT * FROM sys.statement_analysis LIMIT 1G *************************** 1. row *************************** query: INSERT INTO `mem__quan` . `nor ... nDuration` = IF ( VALUES ( ... db: mem full_scan: 0 exec_count: 1110067 err_count: 0 warn_count: 0 total_latency: 1.93h max_latency: 5.03 s avg_latency: 6.27 ms lock_latency: 00:18:29.18 Example rows_sent: 0 rows_sent_avg: 0 rows_examined: 0 rows_examined_avg: 0 tmp_tables: 0 tmp_disk_tables: 0 rows_sorted: 0 sort_merge_passes: 0 digest: d48316a218e95b1b8b72db5e6b177788! first_seen: 2014-05-20 10:42:17

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 22 EXPLAIN • Use EXPLAIN to print the final query plan: • Explain for a running query (New in MySQL 5.7): EXPLAIN FOR CONNECTION connection_id; Understand the query plan EXPLAIN SELECT * FROM t1 JOIN t2 ON t1.a = t2.a WHERE b > 10 AND c > 10; +----+--------+-------+------------+------+---------------+-----+---------+-----+------+----------+------------+ | id | select…| table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+--------+-------+------------+------+---------------+-----+---------+-----+------+----------+------------+ | 1 | SIMPLE | t1 | NULL | range| idx1 | idx1| 4 | NULL| 12 | 33.33 | Using where| | 1 | SIMPLE | t2 | NULL | ref | idx2 | idx2| 4 | t1.a| 1 | 100.00 | NULL | +----+--------+-------+------------+------+---------------+-----+---------+-----+------+----------+------------+

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 23 Added in MySQL 5.7 Structured EXPLAIN • JSON format: • Contains more information: – Used index parts – Pushed index conditions – Cost estimates – Data estimates EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE b > 10 AND c > 10; EXPLAIN { "query_block": { "select_id": 1, "cost_info": { "query_cost": "17.81" }, "table": { "table_name": "t1", "access_type": "range", "possible_keys": [ "idx1" ], "key": "idx1", "used_key_parts": [ "b" ], "key_length": "4", "rows_examined_per_scan": 12, "rows_produced_per_join": 3, "filtered": "33.33", "index_condition": "(`test`.`t1`.`b` > 10)", "cost_info": { "read_cost": "17.01", "eval_cost": "0.80", "prefix_cost": "17.81", "data_read_per_join": "63" }, ……… "attached_condition": "(`test`.`t1`.`c` > 10)" } } } EXPLAIN FORMAT=JSON SELECT …

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 24 EXPLAIN { "query_block": { "select_id": 1, "nested_loop": [ { "table": { "table_name": "t1", "access_type": "ALL", "rows": 10, "filtered": 100, "attached_condition": "(t1.a = 9)" } /* table */ }, { "table": { "table_name": "t2", "access_type": "ALL", "rows": 10, "filtered": 100, "using_join_buffer": "Block Nested Loop", "attached_condition": "((t2.a = 9) and ((t2.b <= 3) or ((t2.b = 5) and (t1.b = 12))))" } /* table */ } ] /* nested_loop */ } /* query_block */ } Structured EXPLAIN Assigning Conditions to Tables EXPLAIN FORMAT=JSON SELECT * FROM t1, t2 WHERE t1.a=t2.a AND t2.a=9 AND (NOT (t1.a > 10 OR t2.b >3) OR (t1.b=t2.b+7 AND t2.b = 5));

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 25 Optimizer Trace: Query Plan Debugging • EXPLAIN shows the selected plan • Optimizer trace shows WHY the plan was selected SET optimizer_trace= "enabled=on"; SELECT * FROM t1,t2 WHERE f1=1 AND f1=f2 AND f2>0; SELECT trace FROM information_schema.optimizer_trace INTO OUTFILE <filename> LINES TERMINATED BY ''; SET optimizer_trace="enabled=off"; QUERY SELECT * FROM t1,t2 WHERE f1=1 AND f1=f2 AND f2>0; TRACE "steps": [ { "join_preparation": { "select#": 1,… } … } …] MISSING_BYTES_BEYOND_MAX_MEM_SIZE 0 INSUFFICIENT_PRIVILEGES 0

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 27 Selecting Access Method • For each table, find the best access method: – Check if the access method is useful – Estimate cost of using access method – Select the cheapest to be used • Choice of access method is cost based Finding the optimal method to read data from storage engine Main access methods:  Table scan  Index scan  Index look-up (ref access)  Range scan  Index merge  Loose index scan

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 28 Ref Access EXPLAIN SELECT * FROM customer WHERE c_custkey = 570887; Single Table Queries id select type table type possible keys key key len ref rows extra 1 SIMPLE customer const PRIMARY PRIMARY 4 const 1 NULL EXPLAIN SELECT * FROM orders WHERE o_orderdate = '1992-09-12'; id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ref i_o_orderdate i_o_orderdate 4 const 6271 NULL

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 29 Ref Access Join Queries EXPLAIN SELECT * FROM orders JOIN customer ON c_custkey = o_custkey WHERE o_orderdate = '1992-09-12'; id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ref i_o_orderdate, i_o_custkey i_o_orderdate 4 const 6271 Using where 1 SIMPLE customer eq_ref PRIMARY PRIMARY 4 dbt3.orders. o_custkey 1 NULL

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 30 Range Optimizer • Goal: find the "minimal" ranges for each index that needs to be read • Example: SELECT * FROM t1 WHERE (key1 > 10 AND key1 < 20) AND key2 > 30 • Range scan using INDEX(key1): • Range scan using INDEX(key2): 10 20 30

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 31 Range Optimizer: Case Study SELECT * FROM orders WHERE YEAR(o_orderdate) = 1997 AND MONTH(o_orderdate) = 5 AND o_clerk = 'Clerk#000001866'; Why table scan? id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ALL NULL NULL NULL NULL 15000000 Using where Index not considered mysql> SELECT * FROM orders WHERE year(o_orderdate) = 1997 AND MONTH(… ... 15 rows in set (8.91 sec)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 32 Range Optimizer: Case Study SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND '1997-05-31' AND o_clerk = 'Clerk#000001866'; Rewrite query to avoid functions on indexed columns id select type table type possible keys key key len ref rows extra 1 SIMPLE orders range i_o_orderdate i_o_orderdate 4 NULL 376352 Using index condition; Using where mysql> SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND … ... 15 rows in set (0.91 sec)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 33 Range Optimizer: Case Study CREATE INDEX i_o_clerk ON orders(o_clerk); SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND '1997-05-31' AND o_clerk = 'Clerk#000001866'; Adding another index id select type table type possible keys key key len ref rows extra 1 SIMPLE orders range i_o_orderdate, i_o_clerk i_o_clerk 16 NULL 1504 Using index condition; Using where mysql> SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND … ... 15 rows in set (0.01 sec)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 34 Range Access for Multi-Column Indexes • Table: • INDEX idx(a, b, c); • Logical storage layout of index: Example table with multi-part index 10 1 2 3 4 5 10 11 1 2 3 4 5 12 1 2 3 4 5 13 1 2 3 4 5 a b c 11 12 pk a b c

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 35 Range Access for Multi-Column Indexes, cont • Equality on 1st index column? – Can add condition on 2nd index column to range condition • Example: SELECT * from t1 WHERE a IN (10,11,13) AND (b=2 OR b=4) • Resulting range scan: 10 1 2 3 4 5 11 1 2 3 4 5 12 1 2 3 4 5 13 1 2 3 4 5 a b c 2 4 2 4 2 4

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 36 Range Access for Multi-Column Indexes, cont • Non-Equality on 1st index column: – Can NOT add condition on 2nd index column to range condition • Example: SELECT * from t1 WHERE a > 10 AND a < 13 AND (b=2 OR b=4) • Resulting range scan: 10 1 2 3 4 5 11 1 2 3 4 5 12 1 2 3 4 5 13 1 2 3 4 5 a b c a >10 AND a < 13

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 37 Range Optimizer: Case Study CREATE INDEX i_o_clerk_date ON orders(o_clerk, o_orderdate); SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND '1997-05-31' AND o_clerk = 'Clerk#000001866'; Create multi-column index id select type table type possible keys key key len ref rows extra 1 SIMPLE orders range i_o_orderdate, i_o_clerk, i_o_clerk_date i_o_clerk_date 20 NULL 14 Using index condition mysql> SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' AND … ... 15 rows in set (0.00 sec)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 38 Performance Schema: Query History UPDATE performance_schema.setup_consumers SET enabled='YES' WHERE name = 'events_statements_history'; mysql> SELECT sql_text, (timer_wait)/1000000000.0 "t (ms)", rows_examined rows FROM performance_schema.events_statements_history ORDER BY timer_start; +---------------------------------------------------------------+--------+------+ | sql_text | t (ms) | rows | +---------------------------------------------------------------+--------+------+ | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 8.1690 | 1505 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 7.2120 | 1505 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 8.1613 | 1505 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 7.0535 | 1505 | | CREATE INDEX i_o_clerk_date ON orders(o_clerk,o_orderdate) |82036.4190 | 0 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 0.7259 | 15 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 0.5791 | 15 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 0.5423 | 15 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 0.6031 | 15 | | SELECT * FROM orders WHERE o_orderdate BETWEEN '1997-05-01' … | 0.2710 | 15 | +---------------------------------------------------------------+--------+------+ MySQL 5.7: Enabled by default

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 40 Join Optimizer • Goal: Given a JOIN of N tables, find the best JOIN ordering • Strategy: – Start with all 1-table plans (Sorted based on size and key dependency) – Expand each plan with remaining tables • Depth-first – If “cost of partial plan” > “cost of best plan”: • “prune” plan – Heuristic pruning: • Prune less promising partial plans • May in rare cases miss most optimal plan (turn off with set optimizer_prune_level = 0) ”Greedy search strategy” t1 t2 t2 t2 t2 t3 t3 t3 t4t4 t4 t4t4 t3 t3 t2 t4t2 t3 N! possible plans

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 41 JOIN Optimizer Illustrated SELECT City.Name, Language FROM Language, Country, City WHERE City.CountryCode = Country.Code AND City.ID = Country.Capital AND City.Population >= 1000000 AND Language.Country = Country.Code; Language Country City LanguageCountry Country City CityCity City cost=26568 cost=32568 cost=627 cost=1245 cost=862 start

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 42 Join Optimizer: Case study SELECT o_year, SUM(CASE WHEN nation = 'FRANCE' THEN volume ELSE 0 END) / SUM(volume) AS mkt_share FROM ( SELECT EXTRACT(YEAR FROM o_orderdate) AS o_year, l_extendedprice * (1 - l_discount) AS volume, n2.n_name AS nation FROM part JOIN lineitem ON p_partkey = l_partkey JOIN supplier ON s_suppkey = l_suppkey JOIN orders ON l_orderkey = o_orderkey JOIN customer ON o_custkey = c_custkey JOIN nation n1 ON c_nationkey = n1.n_nationkey JOIN region ON n1.n_regionkey = r_regionkey JOIN nation n2 ON s_nationkey = n2.n_nationkey WHERE r_name = 'EUROPE' AND o_orderdate BETWEEN '1995-01-01' AND '1996-12-31' AND p_type = 'PROMO BRUSHED STEEL' ) AS all_nations GROUP BY o_year ORDER BY o_year; DBT-3 Query 8: National Market Share Query

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 44 Join Optimizer: Case study SELECT o_year, SUM(CASE WHEN nation = 'FRANCE' THEN volume ELSE 0 END) / SUM(volume) AS mkt_share FROM ( SELECT EXTRACT(YEAR FROM o_orderdate) AS o_year, l_extendedprice * (1 - l_discount) AS volume, n2.n_name AS nation FROM part STRAIGHT_JOIN lineitem ON p_partkey = l_partkey JOIN supplier ON s_suppkey = l_suppkey JOIN orders ON l_orderkey = o_orderkey JOIN customer ON o_custkey = c_custkey JOIN nation n1 ON c_nationkey = n1.n_nationkey JOIN region ON n1.n_regionkey = r_regionkey JOIN nation n2 ON s_nationkey = n2.n_nationkey WHERE r_name = 'EUROPE' AND o_orderdate BETWEEN '1995-01-01' AND '1996-12-31' AND p_type = 'PROMO BRUSHED STEEL' ) AS all_nations GROUP BY o_year ORDER BY o_year; Force early processing of high selectivity predicates Highest selectivity part before lineitem

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 46 MySQL 5.7: Cost Information in Structured EXPLAIN Accumulated cost Total query cost Cost per table Improvements to Query 8 in MySQL 5.7: • Filtering on non-indexed columns are taken into account – No need for hint to force part table to be processed early • Merge derived tables into outer query – No temporary table

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 48 ORDER BY Optimizations • General solution; “Filesort”: – Store query result in temporary table before sorting – If data volume is large, may need to sort in several passes with intermediate storage on disk. • Optimizations: – Take advantage of index to generate query result in sorted order – For ”LIMIT n” queries, maintain priority queue of n top items in memory instead of filesort. (MySQL 5.6)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 49 Filesort SELECT * FROM orders ORDER BY o_totalprice ; SELECT c_name, o_orderkey, o_totalprice FROM orders JOIN customer ON c_custkey = o_custkey WHERE c_acctbal < -1000 ORDER BY o_totalprice ; id select type table type possible keys key key len ref rows extra 1 SIMPLE customer ALL PRIMARY NULL NULL NULL 1500000 Using where; Using temporary; Using filesort 1 SIMPLE orders ref i_o_custkey i_o_custkey 5 ... 7 NULL id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ALL NULL NULL NULL NULL 15000000 Using filesort

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 51 Filesort Sorting status per statement available from Performance Schema mysql> SELECT sql_text,sort_merge_passes,sort_range,sort_rows,sort_scan FROM performance_schema.events_statements_history ORDER BY timer_start DESC LIMIT 1; +--------------+-------------------+------------+-----------+-----------+ | sql_text | sort_merge_passes | sort_range | sort_rows | sort_scan | +--------------+-------------------+------------+-----------+-----------+ | SELECT ... | 1 | 0 | 136170 | 1 | +--------------+-------------------+------------+-----------+-----------+ Performance Schema

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 53 Filesort: Case Study mysql> SELECT AVG(o_totalprice) FROM (SELECT o_totalprice FROM orders ORDER BY o_totalprice DESC LIMIT 100000) td; +-------------------+ | AVG(o_totalprice) | +-------------------+ | 398185.986158 | +-------------------+ 1 row in set (8.18 sec) mysql> SELECT sql_text, sort_merge_passes FROM performance_schema. events_statements_history ORDER BY timer_start DESC LIMIT 1; +----------------------------------------------------+-------------------+ | sql_text | sort_merge_passes | +----------------------------------------------------+-------------------+ | SELECT AVG(o_totalprice) FROM (SELECT o_totalprice | 229 | +----------------------------------------------------+-------------------+ Reduce amount of data to be sorted

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 54 Filesort: Case Study mysql> SET sort_buffer_size = 1024*1024; mysql> SELECT AVG(o_totalprice) FROM (SELECT o_totalprice FROM orders ORDER BY o_totalprice DESC LIMIT 100000) td; +-------------------+ | AVG(o_totalprice) | +-------------------+ | 398185.986158 | +-------------------+ 1 row in set (7.24 sec) mysql> SELECT sql_text, sort_merge_passes FROM performance_schema. events_statements_history ORDER BY timer_start DESC LIMIT 1; +----------------------------------------------------+-------------------+ | sql_text | sort_merge_passes | +----------------------------------------------------+-------------------+ | SELECT AVG(o_totalprice) FROM (SELECT o_totalprice | 57 | +----------------------------------------------------+-------------------+ Increase sort buffer (1 MB) Default is 256 kB

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 55 Filesort: Case Study mysql> SET sort_buffer_size = 8*1024*1024; mysql> SELECT AVG(o_totalprice) FROM (SELECT o_totalprice FROM orders ORDER BY o_totalprice DESC LIMIT 100000) td; +-------------------+ | AVG(o_totalprice) | +-------------------+ | 398185.986158 | +-------------------+ 1 row in set (6.30 sec) mysql> SELECT sql_text, sort_merge_passes FROM performance_schema. events_statements_history ORDER BY timer_start DESC LIMIT 1; +----------------------------------------------------+-------------------+ | sql_text | sort_merge_passes | +----------------------------------------------------+-------------------+ | SELECT AVG(o_totalprice) FROM (SELECT o_totalprice | 0 | +----------------------------------------------------+-------------------+ Increase sort buffer even more (8 MB)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 56 Using Index to Avoid Sorting CREATE INDEX i_o_totalprice ON orders(o_totalprice); SELECT o_orderkey, o_totalprice FROM orders ORDER BY o_totalprice ; id select type table type possible keys key key len ref rows extra 1 SIMPLE orders index NULL i_o_totalprice 6 NULL 15000000 Using index SELECT * FROM orders ORDER BY o_totalprice ; However, still (due to total cost): id select type table type possible keys key key len ref rows extra 1 SIMPLE orders ALL NULL NULL NULL NULL 15000000 Using filesort

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 57 Using Index to Avoid Sorting SELECT AVG(o_totalprice) FROM (SELECT o_totalprice FROM orders ORDER BY o_totalprice DESC LIMIT 100000) td; Case study revisited id select type table Type possible keys key key len ref rows extra 1 PRIMARY <derived2> ALL NULL NULL NULL NULL 100000 NULL 2 DERIVED orders index NULL i_o_totalprice 6 NULL 15000000 Using index mysql> SELECT AVG(o_totalprice) FROM ( SELECT o_totalprice FROM orders ORDER BY o_totalprice DESC LIMIT 100000) td; ... 1 row in set (0.06 sec)

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 59 Influencing the Optimizer • Add indexes • Force use of specific indexes: – USE INDEX, FORCE INDEX, IGNORE INDEX • Force specific join order: – STRAIGHT_JOIN • Adjust session variables – optimizer_switch flags: set optimizer_switch="index_merge=off" – Buffer sizes: set sort_buffer=8*1024*1024; – Other variables: set optimizer_search_depth = 10; When the optimizer does not do what you want

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 60 MySQL 5.7: New Optimizer Hints • Ny hint syntax: – SELECT /*+ HINT1(args) HINT2(args) */ … FROM … • New hints: – BKA(tables)/NO_BKA(tables), BNL(tables)/NO_BNL(tables) – MRR(table indexes)/NO_MRR(table indexes) – SEMIJOIN/NO_SEMIJOIN(strategies), SUBQUERY(strategy) – NO_ICP(table indexes) – NO_RANGE_OPTIMIZATION(table indexes) – QB_NAME(name) • Finer granularilty than optimizer_switch session variable

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 61 • Disable semi-join with hint: EXPLAIN SELECT * FROM t2 WHERE t2.a IN (SELECT /*+ NO_SEMIJOIN() */ a FROM t3); • No hint, optimizer chooses semi-join algorithm LooseScan: EXPLAIN SELECT * FROM t2 WHERE t2.a IN (SELECT a FROM t3); MySQL 5.7: Hint Example: SEMIJOIN id select type table type possible keys key key len ref rows extra 1 SIMPLE t3 index a a 4 NULL 3 Using where; LooseScan 1 SIMPLE t2 ref a a 4 test.t3.a 1 Using index id select type table type possible keys key key len ref rows extra 1 PRIMARY t2 index null a 4 NULL 4 Using where; Using index 2 DEPENDENT SUBQUERY t3 Index_ subquery a a 4 func 1 Using index

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 62 MySQL 5.7: Hint Example: SEMIJOIN • Force Semi-join Materialization to be used EXPLAIN SELECT /*+ SEMIJOIN(@subq MATERIALIZATION) */ * FROM t2 WHERE t2.a IN (SELECT /*+ QB_NAME(subq) */ a FROM t3); 3 rows in set, 1 warning (0.01 sec) id select type table type possible keys key key len ref rows extra 1 SIMPLE t2 index a a 4 NULL 4 Using where; Using index 1 SIMPLE <subquery2> eq_ref <auto_key> <auto_key> 4 test.t2.a 1 NULL 2 MATERIALIZED t3 index a a 4 NULL 3 Using index

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 63 MySQL 5.7: Query Rewrite Plugin • Rewrite problematic queries without the need to make application changes – Add hints – Modify join order – Much more … • Add rewrite rules to table: INSERT INTO query_rewrite.rewrite_rules (pattern, replacement ) VALUES ("SELECT * FROM t1 WHERE a > ? AND b = ?", "SELECT * FROM t1 FORCE INDEX (a_idx) WHERE a > ? AND b = ?"); • New pre- and post-parse query rewrite APIs – Users can write their own plug-ins

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 64 More information • My blog: – http://oysteing.blogspot.com/ • Optimizer team blog: – http://mysqloptimizerteam.blogspot.com/ • MySQL Server Team blog – http://mysqlserverteam.com/ • MySQL forums: – Optimizer & Parser: http://forums.mysql.com/list.php?115 – Performance: http://forums.mysql.com/list.php?24

How to analyze and tune sql queries for better performance vts2016

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