MySQL  8.0.22
Source Code Documentation
service_thd_wait.h
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22 
23 #ifndef MYSQL_SERVICE_THD_WAIT_INCLUDED
24 #define MYSQL_SERVICE_THD_WAIT_INCLUDED
25 
26 /**
27  @file include/mysql/service_thd_wait.h
28  This service provides functions for plugins and storage engines to report
29  when they are going to sleep/stall.
30 
31  SYNOPSIS
32  thd_wait_begin() - call just before a wait begins
33  thd Thread object
34  Use NULL if the thd is NOT known.
35  wait_type Type of wait
36  1 -- short wait (e.g. for mutex)
37  2 -- medium wait (e.g. for disk io)
38  3 -- large wait (e.g. for locked row/table)
39  NOTES
40  This is used by the threadpool to have better knowledge of which
41  threads that currently are actively running on CPUs. When a thread
42  reports that it's going to sleep/stall, the threadpool scheduler is
43  free to start another thread in the pool most likely. The expected wait
44  time is simply an indication of how long the wait is expected to
45  become, the real wait time could be very different.
46 
47  thd_wait_end() called immediately after the wait is complete
48 
49  thd_wait_end() MUST be called if thd_wait_begin() was called.
50 
51  Using thd_wait_...() service is optional but recommended. Using it will
52  improve performance as the thread pool will be more active at managing the
53  thread workload.
54 */
55 
56 class THD;
57 #define MYSQL_THD THD *
58 
59 /*
60  One should only report wait events that could potentially block for a
61  long time. A mutex wait is too short of an event to report. The reason
62  is that an event which is reported leads to a new thread starts
63  executing a query and this has a negative impact of usage of CPU caches
64  and thus the expected gain of starting a new thread must be higher than
65  the expected cost of lost performance due to starting a new thread.
66 
67  Good examples of events that should be reported are waiting for row locks
68  that could easily be for many milliseconds or even seconds and the same
69  holds true for global read locks, table locks and other meta data locks.
70  Another event of interest is going to sleep for an extended time.
71 
72  Note that user-level locks no longer use THD_WAIT_USER_LOCK wait type.
73  Since their implementation relies on metadata locks manager it uses
74  THD_WAIT_META_DATA_LOCK instead.
75 */
76 typedef enum _thd_wait_type_e {
89 
90 extern "C" struct thd_wait_service_st {
94 
95 #ifdef MYSQL_DYNAMIC_PLUGIN
96 
97 #define thd_wait_begin(_THD, _WAIT_TYPE) \
98  thd_wait_service->thd_wait_begin_func(_THD, _WAIT_TYPE)
99 #define thd_wait_end(_THD) thd_wait_service->thd_wait_end_func(_THD)
100 
101 #else
102 
103 void thd_wait_begin(MYSQL_THD thd, int wait_type);
104 void thd_wait_end(MYSQL_THD thd);
105 
106 #endif
107 
108 #endif
enum _thd_wait_type_e thd_wait_type
Definition: service_thd_wait.h:83
Definition: service_thd_wait.h:90
void(* thd_wait_end_func)(MYSQL_THD)
Definition: service_thd_wait.h:92
Definition: service_thd_wait.h:86
Definition: service_thd_wait.h:80
void thd_wait_begin(MYSQL_THD thd, int wait_type)
Definition: sql_thd_api.cc:615
Definition: service_thd_wait.h:81
#define MYSQL_THD
Definition: service_thd_wait.h:57
wait_type
Definition: socket_constants.h:85
Definition: service_thd_wait.h:78
Definition: service_thd_wait.h:84
_thd_wait_type_e
Definition: service_thd_wait.h:76
Definition: service_thd_wait.h:79
void(* thd_wait_begin_func)(MYSQL_THD, int)
Definition: service_thd_wait.h:91
Definition: service_thd_wait.h:77
Definition: service_thd_wait.h:82
Definition: service_thd_wait.h:87
void thd_wait_end(MYSQL_THD thd)
Interface for MySQL Server, plugins and storage engines to report when they waking up from a sleep/st...
Definition: sql_thd_api.cc:626
struct thd_wait_service_st * thd_wait_service
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_class.h:803
Definition: service_thd_wait.h:85