MySQL Performance Schema : fossasia

MySQL Performance SchemaOverview and new exciting features

Mayank PrasadPrincipal Member Technical StaffOracle, MySQLMarch 15, 2015

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Program Agenda

Need, Origin and Design

Instruments and instrumentation

Use cases

Configuration

Benefits and Restrictions

What’s new in MySQL 5.7 DMRs

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Program Agenda



Use cases

Configuration



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Why Performance Schema?

SystemLow throughput?

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DBA

Hot table?

Network

High traffic on link?

Storage

Too much Disk spin?App Developer

Slow application?

MySQL Developer

Code contention?

End User

stuck session?


History and Origin

“Performance Schema is a mechanism to give user an insight of what is happening behind the scene when MySQL server is running.”

Development was started by Marc Alff in 2008. He is Chief Architect and Lead of Performance Schema Team (Christopher Powers and me) in Oracle-MySQL.

Introduced in MySQL 5.5.• New storage engine : Performance Schema• New Database : performance_schema• Statistics stored in tables (hard coded DDLs). • Non persistent data.• SQL user interface.

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MySQL 5.7 Performance Schema : DesignBlock Diagram

MySQLServer

Instrumentation points(P_S hooks)

P_S Internal Buffers

P_SStorageEngine

StorageEngine

InterfaceStatisticsReport

FetchData

SQL Query

Collect DataStoreData

P_STables

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Program Agenda



Use cases

Configuration



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Instruments

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• Name of monitored activity.

• Tree like structure. Separated by ‘/’.

• Left to right : More generic to more specific.

• 983 instruments till MySQL 5.7.6 DMR.

• Stored in performance_schema.setup_instruments table.

wait/io/file/myisam/logstatement/sql/select


Instruments contd…Table setup_instruments

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SETUP_INSTRUMENTS

NAME ENABLED TIMED

statement/sql/select YES YES

statement/sql/create_table YES NO

statement/com/Create DB NO NO

… …

stage/sql/closing tables NO NO

stage/sql/Opening tables NO NO

stage/sql/optimizing YES YES

Configurable at run time


Program Agenda



Use cases

Configuration



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What does Performance Schema provide …update performance_schema.setup_instruments set ENABLED='YES', TIMED='YES';

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Connection 1 (Thread 24)start transaction;

insert into test.t1 values('11'); commit;start transaction;

insert into test.t1 values('12'); commit;start transaction;

insert into test.t1 values('13'); commit;select * from test.t1;

Connection 2 (Thread 25)start transaction;insert into test.t2 values('21');

commit;

start transaction;insert into test.t2 values('22'); commit;


What does Performance Schema provide … (cont.)Statements Statistics

* Timer unit is PICOSECOND.

EVENTS_STATEMENTS_CURRENT

THREAD_ID 24 25

EVENT_NAMEstatement/sql/select

statement/sql/commit

TIMER_WAIT 876585000 15998287000

SQL_TEXTselect * from test.t1

commit

ROWS_SENT 3 0

NO_INDEX_USED 0 0

SELECT_SCAN 1 0

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EVENTS_STATEMENTS_SUMMARY_BY_THREAD_BY_EVENT_NAME

THREAD_ID 24 25

EVENT_NAMEstatement/sql/insert

statement/sql/insert

COUNT_STAR 3 2

SUM_TIMER_WAIT 35181659000 3477432000

SUM_ROWS_AFFECTED 3 2

SUM_SELECT_SCAN 0 0

SUM_NO_INDEX_USED 0 0


What does Performance Schema provide … (cont.)Statements Statistics (cont.)

* Timer unit is PICOSECOND.

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EVENTS_STATEMENTS_SUMMARY_GLOBAL_BY_EVENT_NAME

EVENT_NAME statement/sql/insert statement/sql/commit

COUNT_STAR 5 5

SUM_TIMER_WAIT 38659091000 65812216000

… …

SUM_ROWS_AFFECTED 5 0

… … …


Use case 1Revisited

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• Multiple queries running for long on MySQL Server

• Few long running query (taking lots of time)

• No idea which one

• No idea why

• What to do ? …


Use case 1Diagnosis

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– THREAD_ID: 25

– EVENT_ID: 89

– EVENT_NAME: statement/sql/select

– SQL_TEXT : select bla bla bla…;

• Wait ! There’s more!

– SELECT_SCAN : 1

– NO_INDEX_USED: 1

• Aha !!

SELECT * FROM events_statements_history WHERE TIMER_WAIT > ‘X’;


Use case 2Statements giving errors ( or warnings)

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SELECT DIGEST_TEXT, SCHEMA_NAME, COUNT_STAR, SUM_ERRORS, SUM_WARNINGSFROM performance_schema.events_statements_summary_by_digestWHERE SUM_ERRORS > 0 ORDER BY SUM_ERRORS DESC limit 1\G;

EVENTS_STATEMENTS_SUMMARY_BY_DIGEST

DIGEST_TEXT CREATE TEMPORARY TABLE IF NOT ... _logs` ( `id` INT8 NOT NULL )!

SCHEMA_NAME mem

COUNT_STAR 1725

SUM_ERRORS 1725

SUM_WARNINGS 0

FIRST_SEEN 2014-05-20 10:42:32

LAST_SEEN 2014-05-21 18:39:22


Use case 3Description

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• Multithreaded environment

• My session is stuck

• No idea why

• What to do ? …


Use case 3

• What T1 is waiting for

– Say T1 is waiting for mutex_A (column OBJECT_INSTANCE_BEGIN)

• Lets see who has taken this mutex_A

– Ok, so thread T2 is holding mutex_A (column LOCKED_BY_THREAD_ID)

• Find out what thread t2 is waiting for

• And so on…

SELECT * FROM mutex_instances WHERE OBJECT_INSTANCE_BEGIN = mutex_A;

SELECT * FROM events_waits_current WHERE THREAD_ID = T2;

Diagnosis

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SELECT * FROM events_waits_current WHERE THREAD_ID = T1;


Event Hierarchy

Session

Transaction

*Statement

Stage

Waitsync, lock, i/o

* Statements for non-transactions tables are not part of Transaction instrumentation.

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Event Hierarchy

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event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

event_id

nesting_event_id

Transactions Statements Stages Waits


Instruments availableMonitored activities

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• Instrumentation for

– I/O operation (file, table, NET)

– Locking (mutex, r/w locks, table locks, MDLs)

– EVENT (transactions, statements, stages, waits, idle)

– Stored Programs (Procedures, Functions, Triggers, Events)

– User/host/account

– Memory

– And many more …


Program Agenda



Use cases

Configuration



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Configuration

• Build

• Startup

– Configuration file

– Command line

• Runtime

[mysqld]

performance_schema_consumers_event_waits_history = ON.

performance_schema_events_waits_history_size = 1000.

performance_schema_instruments=‘statement/sql/% = COUNTED’

--performance_schema_consumers_event_waits_history = ON.

--performance_schema_events_waits_history_size = 1000

cmake . -DWITH_PERFSCHEMA_STORAGE_ENGINE=1 -DDISABLE_PSI_MUTEX=1

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update setup_consumers set ENABLED=‘NO’ where NAME=‘global_instrumentation’;.

update setup_instruments set ENABLED=‘YES’ where NAME=‘statement/sql/%’;


Program Agenda



Use cases

Configuration



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Performance Schema Benefits & Restriction

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Benefits

• Great insight of a running MySQL server.

• Good granularity (nested events).

• Available irrespective of platforms.

• User friendly SQL interface.

• Multiple summary tables for consolidation.

• Dynamically configurable to meet user's need at run time.

Restriction

• Performance overhead.

– Configure as per need.


Program Agenda



Use cases

Configuration



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• Instrumentation For:

– Transactions

– Meta data locks

– Prepared statements

– Stored programs

– Memory usage

• User variables

• Replication Summary Tables

• Status Variables (session/global)

• Scalable Memory Allocation

• Reduced Memory footprint

• Configurable Digest Size

• 87 Tables and 983 Instruments

Thank You!

Q&A ?


Software

MySQL Performance Schema : fossasia