Georgi Kodinov gave a presentation on instrumenting code in the MySQL Performance Schema. He discussed why developers should instrument their code, how to do so, and the mechanics behind it. Instrumenting code provides insight into resource usage and makes code more debuggable and portable. It also exposes extra information to users and administrators. The Performance Schema allows adding new tables from components to store volatile data beyond just performance metrics.

1. Georgi Kodinov
Team Lead, MySQL server general team
How to Instrument Your Code in
MySQL Performance Schema
© 2019 Oracle1

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2 © 2019 Oracle

3. Topics Covered
Why should I instrument my code ?
How do I go about instrumenting it ?
Mechanics of instrumentation
PERFORMANCE_SCHEMA: not just about performance
© 2019 Oracle3

4. Why should I instrument my code ?
• Understand what resources it uses:
• memory, locks, time, files, etc.
• More debuggable
• Provides extra insight into code operation and issues
• Expose extra volatile information to users and administrators
• Make your code more portable
© 2019 Oracle4

5. How do I instrument my code ?
Contribute data to the instruments provided
Future: add your own instruments
© 2019 Oracle5

6. Most of the times it’sTHAT easy !
#include <pthread.h>
pthread_mutex_t foo;
void do_something()
{
pthread_mutex_lock(&foo);
...
pthread_mutex_unlock(&foo);
}
#include "mysql/psi/mysql_mutex.h“
mysql_mutex_t foo;
void do_something()
{
mysql_mutex_lock(&foo);
...
mysql_mutex_unlock(&foo);
}
© 2019 Oracle6

7. Extra step: register your objects
#ifdef HAVE_PSI_MUTEX_INTERFACE
PSI_mutex_key mutex_key_foo = PSI_NOT_INSTRUMENTED;
static PSI_mutex_info all_mutexes[]=
{
{ &mutex_key_foo, "LOCK_foo", PSI_FLAG_SINGLETON, 0, "example doc"},
..
}
..
count = static_cast<int>(array_elements(all_mutexes));
mysql_mutex_register(“category_foo”, all_mutexes, count);
..
mysql_mutex_init(mutex_key_foo, &foo, MY_MUTEX_INIT_FAST);
#endif /* HAVE_PSI_MUTEX_INTERFACE */
© 2019 Oracle7

8. Instrumentation inventory: inline functions
• POSIX threads
• POSIX conditions
• POSIX mutexes
• POSIX read/write locks
• POSIX sockets
• Buffered and unbuffered file I/O
• MySQL stages
• MySQL metadata locks
mysql_thread.h
mysql_cond.h
mysql_mutex.h
mysql_rwlock.h
mysql_socket.h
mysql_file.h
mysql_stage.h
mysql_mdl.h
© 2019 Oracle8

9. How do I instrument my memory use ?
#include <stdlib.h>
void *foo;
void do_something()
{
foo = malloc(12);
...
free(foo);
}
#include "mysys.h“
void *foo;
void do_something()
{
foo = my_malloc(mem_key_foo, 12, MYF(0));
...
my_free(foo);
}
© 2019 Oracle9

10. Extra step: register your objects
#ifdef HAVE_PSI_MEMORY_INTERFACE
PSI_memory_key mem_key_foo = PSI_NOT_INSTRUMENTED;
static PSI_memory_info all_memory[] = {
{&mem_key_foo, “FOO", PSI_FLAG_ONLY_GLOBAL_STAT, 0, "example doc"}};
…
count = static_cast<int>(array_elements(all_memory));
mysql_memory_register(category, all_memory, count);
#endif /* HAVE_PSI_MEMORY_INTERFACE */
© 2019 Oracle10

11. Instrumentation inventory: memory
• Plugin service implemented in mysys:
my_malloc(), my_free(), my_memdup()
etc.
• Static mysys inspired library to link with
components: just my_malloc() and my_free()
include/mysql/service_mysql_alloc.h
components/library_mysys/my_memory.h
© 2019 Oracle11

12. Instrumenting other stuff: utility macros
#include <mysql/psi/mysql_idle.h>
…
PSI_idle_locker *m_idle_psi = NULL;
PSI_idle_locker_state m_idle_state;
…
MYSQL_START_IDLE_WAIT(m_idle_psi, &m_idle_state);
…
MYSQL_END_IDLE_WAIT(m_idle_psi);
…
© 2019 Oracle12

13. Instrumentation inventory: utility macros
• Transactions
• Table locks
• “System” (currently shared objects)
• Statements
• Stored programs
• Prepared statements
• MySQL stages
• Errors
• Data locks
 Idle
mysql_transaction.h
mysql_table.h
mysql_system.h
mysql_statement.h
mysql_sp.h
mysql_ps.h
mysql_stage.h
mysql_error.h
mysql_data_lock.h
mysql_idle.h
© 2019 Oracle13

14. Mechanics of code instrumentation
Under the hood
© 2019 Oracle14

15. Calling instrumentation: PSI_*_CALL macros
• Server code: direct call
• #define PSI_FILE_CALL(M) pfs_##M##_v1
• Plugins: function pointer
• #define PSI_FILE_CALL(M) psi_file_service->M
• Components: component service handle
• #define PSI_FILE_CALL(M) mysql_service_psi_file_v1->M
© 2019 Oracle15

16. Random thoughts on good code instrumentation
• Always release the artifacts that instruments returned via the
intended methods !
• Instrumentation can be costly !
• Consider using component infrastructure
© 2019 Oracle16

17. Performance Schema
Not just about performance !
© 2019 Oracle17

18. PERFORMANCE_SCHEMA: Not just performance !
• Started as performance instrumentation. Still does it !
• Grown into general storage for fast-changing volatile data
• System variables
• Connection attributes
• Replication, innodb state
• Now supports adding new tables from components
© 2019 Oracle18

19. Add a PERFORMANCE_SCHEMA table
From a component
© 2019 Oracle19

20. Step 1:The data
© 2019 Oracle20

21. Step 2: Basic table APIs
© 2019 Oracle21

22. Step 3: Data retrieval
© 2019 Oracle22

23. Step 4: Component code
© 2019 Oracle23

24. How it drives
© 2019 Oracle24

25. Let’s look at the table
© 2019 Oracle25

26. Where to go from here ?
• MySQL Internals Doxygen:
https://dev.mysql.com/doc/dev/mysql-
server/latest/PAGE_PFS.html
• Reference Manual:
https://dev.mysql.com/doc/refman/8.0/en/performance-
schema.html
© 2019 Oracle26

27. Questions And Answers
© 2019 Oracle27

28. Copyright © 2019 Oracle and/or its affiliates.28
Meet the MySQL Team at the Conference
Sunny Bains
Luis Soares
Kenny Gryp
Frédéric Descamps
Dimitri Kravtchuk
Ståle Deraas
Pedro Gomes
Geir HøydalsvikNorvald Ryeng
Georgi Kodinov

29. Join us on MySQL Community Slack
Copyright © 2019 Oracle and/or its affiliates.29
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31. Thank you !
Georgi “Joro” Kodinov
Team Lead,
MySQL Server GeneralTeam
Georgi.Kodinov@oracle.com
31 © 2019 Oracle