MySQL Performance Tuning - GNUnify 2010

Secrets of Best MySQL Optimization presented by Sonali Minocha OSSCube

Who Am I?

Why Tune a Database?

Who Tunes?

What is Tuned?

How much tuning is enough?

Application Development (Optimizing Queries)

Index Optimizations

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

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 for each record The read type is optimized individually for each combination of rows from the previous tables

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

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

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

Database Designing (Optimizing Schemas)

Normalization

Table Optimizations

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

MyISAM-Specific Optimizations

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

Monitoring Threads in MySQL

MEMORY-Specific Optimizations

Optimizing the Server

Performance Monitoring

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

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

Status Variables

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

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

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

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

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

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

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

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

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)

innodb_flush_log_at_trx_commit (default 1)
0 writes and sync’s once per second (not ACID)
1 forces sync to disk after every commit
2 write to disk every commit but only sync’s about once per second

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

Thank you for your time and attention For more information, please feel free to drop in a line to [email_address] or visit http://www.osscube.com www.osscube.com

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MySQL Performance Tuning - GNUnify 2010

by OSSCube LLC A Global Open Source Enterprise for Open Source Solutions on Mar 08, 2010

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MySQL Performance Tuning - GNUnify 2010 — Presentation Transcript