MySQL Performance Schema : fossasia

MySQL Performance Schema
Overview and new exciting features
Mayank Prasad
Principal Member Technical Staff
Oracle, MySQL
March 15, 2015
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information purposes only, and may not be incorporated into any contract. It is not a
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2

Program Agenda
Need, Origin and Design
Instruments and instrumentation
Use cases
Configuration
Benefits and Restrictions
What’s new in MySQL 5.7 DMRs
1
2
3
4
5
6
3

Program Agenda
Use cases
Configuration
1
2
3
4
5
6
4

Why Performance Schema?
System
Low throughput?
?
5
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.
6

MySQL 5.7 Performance Schema : Design
Block Diagram
MySQL
Server
Instrumentation points
(P_S hooks)
P_S Internal Buffers
P_S
Storage
Engine
Storage
Engine
Interface
Statistics
Report
Fetch
Data
SQL Query
Collect Data
Store
Data
P_S
Tables
7

Program Agenda
Use cases
Configuration
1
2
3
4
5
6
8

Instruments
9
• 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/log
statement/sql/select

Instruments contd…
Table setup_instruments
10
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
1
2
3
4
5
6
11

What does Performance Schema provide …
update performance_schema.setup_instruments set ENABLED='YES', TIMED='YES';
12
Connection 1 (Thread 24)
start transaction;
insert into test.t1 values('11');
commit;
start transaction;
commit;
start transaction;
commit;
select * from test.t1;
Connection 2 (Thread 25)
start transaction;
commit;
start transaction;
commit;

What does Performance Schema provide … (cont.)
Statements Statistics
* Timer unit is PICOSECOND.
EVENTS_STATEMENTS_CURRENT
THREAD_ID 24 25
EVENT_NAME
statement/sql
/select
statement/sql/
commit
TIMER_WAIT 876585000 15998287000
SQL_TEXT
select * from
test.t1
commit
ROWS_SENT 3 0
NO_INDEX_USED 0 0
SELECT_SCAN 1 0
13
EVENTS_STATEMENTS_SUMMARY_BY_THREAD_BY_EVENT
_NAME
THREAD_ID 24 25
EVENT_NAME
statement/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.
14
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 1
Revisited
15
• 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 1
Diagnosis
16
– 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 2
Statements giving errors ( or warnings)
17
SELECT DIGEST_TEXT, SCHEMA_NAME, COUNT_STAR, SUM_ERRORS, SUM_WARNINGS
FROM performance_schema.events_statements_summary_by_digest
WHERE SUM_ERRORS > 0 ORDER BY SUM_ERRORS DESC limit 1G;
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 3
Description
18
• 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
19
SELECT * FROM events_waits_current WHERE THREAD_ID = T1;

Event Hierarchy
Session
Transaction
*Statement
Stage
Wait
sync, lock, i/o
* Statements for non-transactions tables are not part of Transaction instrumentation.
20

Event Hierarchy
21
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 available
Monitored activities
22
• 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
1
2
3
4
5
6
23

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
24
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
1
2
3
4
5
6
25

Performance Schema Benefits & Restriction
26
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
1
2
3
4
5
6
27

28
• 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 ?

MySQL Performance Schema : fossasia

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