This document discusses optimizing MySQL performance. It covers topics like why tuning is important, who performs tuning, what aspects are tuned, and how much tuning is needed. Specific areas discussed include application development like optimizing queries, index optimizations, storage engines, MySQL parameters, and status variables. The document provides guidance on selecting queries to optimize, database design optimizations, choosing a suitable storage engine, MySQL-specific optimizations, and monitoring and tuning server parameters.

1. MySQL Performance
Secrets
By Rakesh Kumar
OSSCube, Delhi
rakesh@osscube.com

2. Why Tune a Database?

3. Who Tunes?

4. What is Tuned?

5. How much tuning is enough?

8. Application Development
(Optimizing Queries)

10. Index Optimizations

13. MySQL Cluster Tutorial, OSSPAC 09 Singapore, ©
OSSCube

14. EXPLAIN Types
system The table has only one row
const At the most one matching row, treated as a
constant
eq_ref One row per row from previous tables
ref Several rows with matching index value
ref_or_null Like ref, plus NULL values
index_merge Several index searches are merged
unique_subquery Same as ref for some subqueries
index_subquery As above for non-unique indexes
range A range index scan
index The whole index is scanned
ALL A full table scan

15. EXPLAIN Extra
Using index The result is created straight from the index
Using where Not all rows are used in the result
Distinct Only a single row is read per row combination
Not exists A LEFT JOIN missing rows optimization is used
Using filesort An extra row sorting step is done
Using temporary A temporary table is used
Range checked The read type is optimized individually for each
for each record combination of rows from the previous tables

16. Optimizer Hints
STRAIGHT_JOIN Forces the optimizer to join the tables in the
given order
SQL_BIG_RESULTS Together with GROUP BY or DISTINCT tells
the server to use disk-based temp tables
SQL_BUFFER_RESULTS Tells the server to use a temp table, thus
releasing locks early (for table-locks)
USE INDEX Hints to the optimizer to use the given index
FORCE INDEX Forces the optimizer to use the index (if
possible)
IGNORE INDEX Forces the optimizer not the use the index

17. Selecting Queries to Optimize
• The slow query log
– Logs all queries that take longer than
long_query_time
– Can also log all queries that don’t use indexes
with
--log-queries-not-using-indexes
– To log slow administrative commands use
--log-slow-admin-statements
– To analyze the contents of the slow log use
mysqldumpslow

18. • The general query log can be use to analyze:
– Reads vs. writes
– Simple queries vs. complex queries
– etc

19. Database Designing
(Optimizing Schemas)

20. Normalization

21. Table Optimizations

22. Choosing Best Suited Storage Engine
• Understanding benefits and drawbacks of
each storage engine is very important while
designing application.
• Different storage engine has different index
capability ,application need should be kept
in mind while choosing storage engine

23. MyISAM-Specific Optimizations

24. InnoDB-Specific Optimizations
• InnoDB uses clustered indexes
– The length of the PRIMARY KEY is extremely
important
• The rows are always dynamic
– Using VARCHAR instead of CHAR is almost always
better
• Maintenance operations needed after
– Many UPDATE/DELETE operations
• The pages can become underfilled

25. Monitoring Threads in MySQL

26. MEMORY-Specific Optimizations

27. Optimizing the Server

28. Performance Monitoring

29. Tuning MySQL Parameters
• Some MySQL options can be changed online
• The dynamic options are either
– SESSION specific
• Changing the value will only affect the current
connection
– GLOBAL
• Changing the value will affect the whole server
– Both
• When changing the value SESSION/GLOBAL
should be specified

30. • Online changes are not persistant over a
server restart
– The configuration files have to be changed as well
• The current values of all options can be found
with
SHOW SESSION/GLOBAL VARIABLES

31. Status Variables

32. SQL/Parser Model
Client1 Client2 ClientN
MySQL Server
Connection Thread Pool
Query Cache  InnoDB
Storage Engines  MyISAM
 MERGE
Parser Query 101101  MEMORY
 Federated
 ARCHIVE
Optimizer  NDBCluster

33. Query Cache
• Stores SELECT queries and their results
• Purpose: improve performance for
frequently requested data
• The data in the query cache is invalidated as
soon as a modification is done in the table
• Controlled with the query_cache_size
variable

34. • The Qcache_% status variables help
monitoring the cache
– The utilisation ratio: Qcache_hits vs.
Com_select
• The query cache can be emptied with
RESET QUERY CACHE

35. Some Thread Specific Options
• read_buffer_size (default 128Kb) and
read_rnd_buffer_size (default 256Kb)
– Size of cache used for table scanning
– Not equivalent to block size
• The database is not divided into blocks but directly into
records
– Increase if you do many sequential scans
• sort_buffer_size (default 2Mb)
– Size of the GROUP BY / ORDER BY cache
– If more memory is needed it will be taken from the disk
• tmp_table_size (default 32Mb)
– Limit after which temporary tables will not be MEMORYs
anymore, but MyISAM tables

36. Some Global Options
• table_cache (default 64)
– Cache for storing open table handlers
– Increase this if Opened_tables is high
• thread_cache (default 0)
– Number of threads to keep for reuse
– Increase if threads_created is high
– Not useful if the client uses connection pooling

37. • max_connections (default 100)
– The maximum allowed number of simultaneous
connections
– Very important for tuning thread specific memory
areas
– Each connection uses at least thread_stack of
memory

38. MyISAM Global Options
• key_buffer_size (default 8Mb)
– Cache for storing indices
– Increase this to get better index handling
– Miss ratio
(key_reads/key_read_requests) should
be very low, at least < 0.03 (often < 0.01 is
desirable)
• Row caching is handled by the OS

39. MyISAM Thread-Specific Options
• myisam_sort_buffer_size (default
8Mb)
– Used when sorting indexes during
REPAIR/ALTER TABLE
• myisam_repair_threads (default 1)
– Used for bulk import and repairing
– Allows for repairing indexes in multiple threads
• myisam_max_sort_file_size
– The max size of the file used while re-creating
indexes

40. InnoDB-Specific Optimization
• innodb_buffer_pool_size (default
8Mb)
– The memory buffer InnoDB uses to cache both
data and indexes
– The bigger you set this the less disk i/o is
needed
– Can be set very high (up to 80% on a dedicated
system)

41. InnoDB-Specific
Optimization
• innodb_log_buffer_size (default
1Mb)
– Larger values allows for larger transactions to be
logged in memory
– Sensible values range from 1M to 8M
• innodb_log_file_size (default 5Mb)
– Size of each InnoDB redo log file
– Can be set up to buffer_pool_size

42. QnA

43. Thank you for your time and attention
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