MySQL-Performance Schema- What's new in MySQL-5.7 DMRs

MySQL Performance Schema
New enhancements in MySQL 5.7 (DMRs)
MayankPrasad
Principal Member Technical Staff
Oracle, MySQL
October 1, 2014
Copyright © 2014,Oracle and/or its affiliates. All rights reserved. |

Safe Harbor Statement
The following is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle’s products remains at the sole discretion of Oracle.
2

Program Agenda
Need and Origin
The Journey : Then and now …
New in MySQL-5.7 (DMRs)
Configuration
An example
Q&A
1
2
3
4
5
6
3

Program Agenda
Need and Origin
Configuration
An example
Q&A
1
2
3
4
5
6
4

Why Performance Schema?
SystemLow throughput? ?
5
DBAHot table?
NetworkHigh traffic on link?
StorageToo much disk spin?
App Developer Slow application?
MySQL Developer Code contention?
End User Stuck session?

History and Origin
“The Performance Schema is a mechanism to give user an insight of what is happening behind the sceneswhen MySQL server is running.”
Development was started by Marc Alffin 2008. He is Chief Architect and Lead of Performance Schema Team (Christopher Powers and me) at 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
MySQL
Server
Instrumentation points(P_S hooks)
P_S Internal Buffers
P_SStorageEngine
StorageEngineInterface
StatisticsReport
FetchData
SQL Query
Collect Data
StoreDataP_STables
7

Program Agenda
Need and Origin
The journey : Then and now …
Configuration
An example
Q&A
1
2
3
4
5
6
8

The Journey : Then and now..
•MySQL 5.5
•Only waits events
–Mutexwaits
–Conditions waits
–R/W locks waits
–File I/O waits
•Setup_(timers/consumers/instruments) tables
•Few summary tables
•17Tables and 218 Instruments
•MySQL 5.6
•Statements and stages
•Table, Index and network I/O. Table locks
•Host Cache
•User, account, host
•Setup_(actor/objects)
•Multiple summary tables
•Events’ hierarchy
•52Tables and 550Instruments
•MySQL 5.7 (DMRs)
•Instrumentation:
–Transactions
–Metadata locks
–Prepared statements
–Stored programs
–Memory usage
•User variables
•Replication summary tables
•76Tables and 885Instruments
•…
9

Program Agenda
Need and Origin
Configuration
An example
Q&A
1
2
4
3
5
6
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Transaction Instrumentation
•Exposes all aspects of Transactions within server
•Implicit and Explicit
•Quantitative (counts, timing) and Qualitative (isolation level) statistics
•Aggregated across several dimensions (user, account, session etc.)
•Statements to non-transactional tables are ignored (MyISAM)
11

Transaction Instrumentation (cont.)
Transactions stats at runtime
* Units in PICOSECONDs
EVENTS_TRANSACTIONS_SUMMARY_BY_THREAD_ BY_EVENT_NAME
THREAD_ID
23
EVENT_NAME
Transaction
COUNT_STAR
3
SUM_TIMER_WAIT
18558993066000*
…
…
COUNT_READ_WRITE
3
SUM_TIMER_READ_WRITE
18558993066000*
…
…
EVENTS_TRANSACTIONS_CURRENT
THREAD_ID
23
EVENT_ID
11
EVENT_NAME
Transaction
STATE
COMMITTED
TIMER_WAIT
22073180000*
ACCESS_MODE
READ WRITE
ISOLATION LEVEL
REPEATABLE READ
AUTOCOMMIT
NO
12

Event Hierarchy
Session
Transaction
Statement*
Stage(closing tables, preparing, optimizing)
Wait
(sync, lock, i/o)
* Transactional tables only.
13

Event Hierarchy (cont.)
An example
START TRANSACTION;
INSERT INTO test.t1 VALUES(‘3’);
COMMIT;
14

Event Hierarchy (cont.)
An example
START TRANSACTION;
INSERT INTO test.t1 VALUES(‘3’);
COMMIT;
15

Metadata Locks Instrumentation
METADATA_LOCKS
OBJECT_TYPE:
TABLE
OBJECT_SCHEMA:
test
OBJECT_NAME:
tab1
LOCK_TYPE:
SHARED_READ
LOCK_DURATION:
TRANSACTION
LOCK_STATUS:
GRANTED
OWNER_THREAD_ID:
23
OWNER_EVENT_ID:
41
16
wait/lock/metadata/sql/mdl
•What are MDLs?
•Exposes metadata lock dependencies between session.
•Which session holds MDL
•Which session waiting MDL
•Lock request status
–PENDING, GRANTED, KILLED, TIMEDOUT

Stored Programs Instrumentation
•New objects types in setup_objects.
–PROCEDURE
–FUNCTION
–TRIGGER
–EVENT
•Can be configured individually.
•Nesting is maintained.
Triggers, Events, Functions, Procedures
OBJECT_ TYPES
OBJECT_ SCHEMA
OBJECT_ NAME
ENABLED
TIMED
TABLE
test
tab1
YES
NO
PROCEDURE
test
proc1
NO
NO
TRIGGER
db1
trg1
YES
YES
FUNCTION
%
%
NO
NO
EVENT
%
%
NO
NO
SETUP_OBJECTS
17

Stored Programs Instrumentation (contd..)
Example :
create trigger test.trgbefore insert on test.tab1 for each row insert into test.tab2 values ('2');
create procedure test.proc()
BEGIN
select count(*) from test.tab1;
insert into test.tab1 values('123');
END
call test.proc();
EVENTS_STATEMENTS_SUMMARY_BY_PROGRAM
OBJECT_TYPE
OBJECT_ SCHEMA
OBJECT_ NAME
COUNT_ STAR
SUM_TIMER_ WAIT
COUNT_ STATEMENT
SUM_STATEMENTS_ WAIT
SUM_ ERRORS
SUM_ROWS_ AFFECTED
PROCEDURE
test
proc
1
21233759000
2
21126786000
0
1
TRIGGER
test
trg
1
2001201000
1
1976505000
0
1
18

Stored Programs Instrumentation (contd..)
Example : (Nesting)
19
EVENTS_STATEMENTS_HISTORY
EVENT_ID
461
SQL_TEXT
insert into d1.tab1 values('123')
OBJECT_TYPE
PROCEDURE
OBJECT_NAME
proc
NESTING_EVENT_ID
442
EVENTS_STATEMENTS_HISTORY
EVENT_ID
469
SQL_TEXT
insert into d1.tab2 values ('2')
OBJECT_TYPE
TRIGGER
OBJECT_NAME
trg
NESTING_EVENT_ID
461

Prepared Statements Instrumentation
•What are Prepared Statements?
•Exposes Prepared Statements in use by server.
•Covers
–PREPARE <stmt>
–mysql_stmt_prepare()
SQLCOM_PREPARE, COM_STMT_PREPARE
20

Prepared Statements Instrumentation (contd.)
Example
prepare stmt1from “select * from employee where emp_id=?”;
Set @emp_id=12345;
execute stmt1 USING @emp_id;
EVENTS_STATEMENTS_HISTORY_LONG
THREAD_ID: 20
EVENT_ID: 4
EVENT_NAME: statement/sql/prepare_sql
SQL_TEXT: prepare stmt1 from "select * from employee where emp_id=?’;"
…
PREPARED_STATEMENTS_INSTANCES
STATEMENT_ID: 1
STATEMENT_NAME: stmt1
SQL_TEXT: select * from employee where emp_id=?
OWNER_THREAD_ID: 20
OWNER_EVENT_ID: 4
OWNER_OBJECT_TYPE: NULL
OWNER_OBJECT_NAME: NULL
COUNT_EXECUTE: 1
21

User Variables
•Exposes user-defined variables
•Max name limit 64
USER_VARIABLES_BY_THREAD
Set @var_1=12345;
--------
Set @var_2=67890;
USER_VARIABLES_BY_THREAD
THREAD_ID
VARIABLE_NAME
VARIABLE_VALUE
23
var_1
12345
24
var_2
67890
22

Memory Usage Instrumentation
•Aspects covered :
–Memory size
–Operation Count (1M bytes once vs. 1 byte 1M times)
–Low/high watermarks (spikes)
•Aggregation
–Type of memory (various cache, internal buffers)
–Thread/account/user/host
•Memory behavior of code/choice of design
Who is taking what, how much and how many times.
23

Memory Usages Instrumentation (contd..)
MEMORY_SUMMARY_GLOBAL_BY_EVENT_NAME
EVENT_NAME
memory/sql/TABLE
COUNT_ALLOC
1381
COUNT_FREE
924
SUM_NUMBER_OF_BYTES_ALLOC
2059873
SUM_NUMBER_OF_BYTES_FREE
1407432
CURRENT_COUNT_USED
457
HIGH_COUNT_USED
461
CURRENT_NUMBER_OF_BYTES_USED
652441
HIGH_NUMBER_OF_BYTES_USED
669269
•Say :
•T1 : 1MB-2MB
•T2 : 10MB-12MB
•Together :
11MB -14MB
24

Replication Summary Tables
Tables for replication statistics
25
•SHOW SLAVE STATUS (Limitations)
–Lots of information packed together
–No logical division of information
–No cherry picking (difficult for automation)
–Difficult to scale (more new fields)
•Why Performance Schema Tables?
–SQL Interface. Fetch what is required
–Split logically into different tables
–Easier to extend

26
Replication status
Connection Information
Execute Information
Connection Configuration
Connection Status
Execute Configuration
Execute Status
Coordinator/SQL Thread
Worker Thread
replication_connection_configuration
replication_connection_status
replication_execute_status_by_coordinator
replication_execute_status_by_worker
replication_execute_status
replication_execute_configuration

Table
Information
replication_connection_configuration
(Host, Port, User etc.)
replication_connection_status
(Server UUID, Receiverthread ID, Service State etc.)
replication_execute_configuration
(Desired Delay)
replication_execute_status
(Remaining Delay)
replication_execute_status_by_coordinator
(Thread Id, Service State, Last Error info.)
replication_execute_status_by_worker
(WID, WTID, Service State, Last error Info.)
27

Program Agenda
Need and Origin
Configuration
An example
Q&A
1
2
3
5
4
6
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Configuration
•Build
•Startup
–Configuration file
–Command line
[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
29

Configuration (contd..)
•Runtime
•Auto tune (value=-1)
–Use heuristics to compute
•Max number of objects (mutex, rwlocks, files, sockets, threads etc.)
•Memory for statistical data (history, history_long, digest etc.)
•NOT ALL VARIABLES ARE AUTO TUNED.
–Aligned with server tuning
•Use hints from server variables
update setup_consumersset ENABLED=‘NO’ where NAME=‘global_instrumentation’;
. update setup_instrumentsset ENABLED=‘YES’ where NAME=‘statement/sql/%’;
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max_connections
table_open_cache
table_definition_cache
open_files_limit

Program Agenda
Need and Origin
Configuration
An example
Q&A
1
2
3
4
6
5
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An Example
•Lets say thread, with thread id T0, is trying to alter a table tab1 and is hung.
•Now, what T0 is waiting for
–LOCK_STATUS=PENDING and OBJECT_NAME=‘tab1’
•Lets see who has taken MDL on table tab1.
–Thread T1 (column OWNER_THREAD_ID) is holding MDL.
•Is T1 waiting for some MDL?
SELECT * FROM metadata_locksWHERE THREAD_ID = T0;
SELECT * FROM metadata_locksWHERE OBJECT_NAME=‘tab1’, LOCK_STATUS=GRANTED;
SELECT * FROM metadata_locksWHERE OWNER_THREAD_ID = T1, LOCK_STATUS=PENDING;
Diagnose a stuck session
32

An Example (contd…)
•If T1 is not waiting for a MDL, then ?
•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
SELECT * FROM events_waits_currentWHERE THREAD_ID = T1;
SELECT * FROM mutex_instancesWHERE OBJECT_INSTANCE_BEGIN = mutex_A;
SELECT * FROM events_waits_currentWHERE THREAD_ID = T2;
Diagnose a stuck session
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References
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•Blogs:
–http://marcalff.blogspot.com/
–http://www.markleith.co.uk/
–http://mayankmysql.blogspot.in/
•Performance Blog:
–http://dimitrik.free.fr/
•MySQL documentation:
–http://dev.mysql.com/doc/refman/5.7/en/performance-schema.html/

Program Agenda
Need and Origin
Configuration
An example
Q&A
1
2
4
5
6
3
35

Thank You! Q&A ?

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