PLe19 How To Instrument Your Code in performance_schema

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

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, timing, and pricing of any features or functionality described for Oracle’s
products may change and remains at the sole discretion of Oracle Corporation.
2 © 2019 Oracle

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

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

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

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

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

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

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

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

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

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

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

Mechanics of code instrumentation
Under the hood
© 2019 Oracle14

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

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

Performance Schema
Not just about performance !
© 2019 Oracle17

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

Add a PERFORMANCE_SCHEMA table
From a component
© 2019 Oracle19

Step 1:The data
© 2019 Oracle20

Step 2: Basic table APIs
© 2019 Oracle21

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

Copyright © 2019 Oracle and/or its affiliates.28
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