Support changing OS thread priorities

Summary:
Support changing priorities of threads associated with user connections.

This change enables 3 ways to change thread priories:
1. **Change current thread priority** : `set thread_priority=<priority_value>`.
2. **Set default priority for all new threads** :  `set global thread_priority=<priority_value>`.
3. **Change any thread priority** : `set global thread_priority_str=<os-thread-id>:<priority_value>`.

- Priority values take a range of -20 to 19 (the same as nice).
- Non-default priority threads are not leaked into the thread cache: Threads which have non-zero priority will be reset to 0 priority at the end of the connection. The threads will be terminated in the case where such priority-reset is not possible.

Automation will mostly make use of the 1st scenario to change the current connection/thread's priority before starting work, say a backup or a large scan.

- Added a new session variable `thread_priority`.
- Renamed `thread_nice_value` var to `thread_priority_str`.
- a new information_schema table, `thread_priorities` to track the priority of all the threads.

`thread_priority` sysvar:
- takes an integer value, in the range similar to nice.
- If this is set at the session level, the current thread's priority is modified.
- If this is set at the global level, all **new** threads will inherit the modified priority.

`thread_priority_str` sysvar:
- input string format: <os-thread-id>:<priority-value>

INFORMATION_SCHEMA.THREAD_PRIORITIES schema:
```
mysql> describe information_schema.threads;
+------------------+---------------------+------+-----+---------+-------+
| Field            | Type                | Null | Key | Default | Extra |
+------------------+---------------------+------+-----+---------+-------+
| ID               | bigint(21) unsigned | NO   |     | 0       |       |
| SYSTEM_THREAD_ID | bigint(21) unsigned | NO   |     | 0       |       |
| PRIORITY         | bigint(5)           | NO   |     | 0       |       |
+------------------+---------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
```
- ID is the connection id as seen in `show processlist`.
- SYSTEM_THREAD_ID is the unix thread id as seen in `ps`.
- PRIORITY is the thread priority (nice value).

Notable changes:
- CAP_SYS_NICE capability is acquired before changing the thread priority, and dropped after the action is done.
- libcap library is a dependency for this change.
- setuid changed to setresuid.

Reviewed By: mzait

Differential Revision: D22046019

fbshipit-source-id: 372586a058f

config.h.cmake

@@ -102,6 +102,7 @@
 #cmakedefine HAVE_SYS_UTIME_H 1
 #cmakedefine HAVE_SYS_WAIT_H 1
 #cmakedefine HAVE_SYS_PARAM_H 1
+#cmakedefine HAVE_SYS_CAPABILITY_H 1
 
 /* Libraries */
 #cmakedefine HAVE_LIBPTHREAD 1
@@ -116,6 +117,7 @@
 #cmakedefine HAVE_LIBRESOLV 1
 /* Does "struct timespec" have a "sec" and "nsec" field? */
 #cmakedefine HAVE_TIMESPEC_TS_SEC 1
+#cmakedefine HAVE_LIBCAP 1
 
 /* Readline */
 #cmakedefine HAVE_HIST_ENTRY 1

configure.cmake

@@ -291,12 +291,13 @@ IF(UNIX)
   ENDIF()
   MY_SEARCH_LIBS(backtrace execinfo LIBEXECINFO)
   MY_SEARCH_LIBS(timer_create rt LIBRT)
+  MY_SEARCH_LIBS(cap_get_proc cap LIBCAP)
 
   FIND_PACKAGE(Threads)
 
   SET(CMAKE_REQUIRED_LIBRARIES 
     ${LIBM} ${LIBNSL} ${LIBBIND} ${LIBCRYPT} ${LIBSOCKET} ${LIBDL}
-    ${CMAKE_THREAD_LIBS_INIT} ${LIBRT} ${LIBEXECINFO}
+    ${CMAKE_THREAD_LIBS_INIT} ${LIBRT} ${LIBEXECINFO} ${LIBCAP}
   )
   # Need explicit pthread for gcc -fsanitize=address
   IF(CMAKE_USE_PTHREADS_INIT AND CMAKE_C_FLAGS MATCHES "-fsanitize=")
@@ -429,6 +430,9 @@ CHECK_INCLUDE_FILES(sys/event.h HAVE_SYS_EVENT_H)
 CHECK_INCLUDE_FILES(sys/queue.h HAVE_SYS_QUEUE_H)
 CHECK_SYMBOL_EXISTS (TAILQ_FOREACH "sys/queue.h" HAVE_TAILQFOREACH)
 
+# For LIBCAP
+CHECK_INCLUDE_FILES (sys/capability.h HAVE_SYS_CAPABILITY_H)
+
 IF(HAVE_SYS_STREAM_H)
   # Needs sys/stream.h on Solaris
   CHECK_INCLUDE_FILES ("sys/stream.h;sys/ptem.h" HAVE_SYS_PTEM_H)

libmysqld/CMakeLists.txt

@@ -100,7 +100,7 @@ ENDIF()
 SET(LIBS 
   dbug strings regex mysys mysys_ssl vio 
   ${ZLIB_LIBRARY} ${SSL_LIBRARIES} 
-  ${LIBWRAP} ${LIBCRYPT} ${LIBDL}
+  ${LIBWRAP} ${LIBCRYPT} ${LIBDL} ${LIBCAP}
   ${MYSQLD_STATIC_PLUGIN_LIBS}
   sql_embedded
 )

mysql-test/include/as_root.inc

@@ -0,0 +1,3 @@
+if (!$MYSQL_TEST_ROOT){
+  skip Run as root;
+}

mysql-test/r/information_schema-big.result

@@ -79,6 +79,7 @@ COLUMN_STATISTICS	TABLE_SCHEMA
 DATABASE_APPLIED_HLC	DATABASE_NAME
 ADMISSION_CONTROL_QUEUE	SCHEMA_NAME
 SQL_FINDINGS	SQL_ID
+THREAD_PRIORITIES	ID
 SELECT t.table_name, c1.column_name
 FROM information_schema.tables t
 INNER JOIN
@@ -155,3 +156,4 @@ COLUMN_STATISTICS	TABLE_SCHEMA
 DATABASE_APPLIED_HLC	DATABASE_NAME
 ADMISSION_CONTROL_QUEUE	SCHEMA_NAME
 SQL_FINDINGS	SQL_ID
+THREAD_PRIORITIES	ID

mysql-test/r/information_schema.result

@@ -111,6 +111,7 @@ COLUMN_STATISTICS
 DATABASE_APPLIED_HLC
 ADMISSION_CONTROL_QUEUE
 SQL_FINDINGS
+THREAD_PRIORITIES
 columns_priv
 db
 event
@@ -155,6 +156,7 @@ TABLE_CONSTRAINTS	TABLE_CONSTRAINTS
 TABLE_PRIVILEGES	TABLE_PRIVILEGES
 TABLE_STATISTICS	TABLE_STATISTICS
 TRIGGERS	TRIGGERS
+THREAD_PRIORITIES	THREAD_PRIORITIES
 tables_priv	tables_priv
 time_zone	time_zone
 time_zone_leap_second	time_zone_leap_second
@@ -177,6 +179,7 @@ TABLE_CONSTRAINTS	TABLE_CONSTRAINTS
 TABLE_PRIVILEGES	TABLE_PRIVILEGES
 TABLE_STATISTICS	TABLE_STATISTICS
 TRIGGERS	TRIGGERS
+THREAD_PRIORITIES	THREAD_PRIORITIES
 tables_priv	tables_priv
 time_zone	time_zone
 time_zone_leap_second	time_zone_leap_second
@@ -199,6 +202,7 @@ TABLE_CONSTRAINTS	TABLE_CONSTRAINTS
 TABLE_PRIVILEGES	TABLE_PRIVILEGES
 TABLE_STATISTICS	TABLE_STATISTICS
 TRIGGERS	TRIGGERS
+THREAD_PRIORITIES	THREAD_PRIORITIES
 tables_priv	tables_priv
 time_zone	time_zone
 time_zone_leap_second	time_zone_leap_second
@@ -694,6 +698,7 @@ TABLE_CONSTRAINTS
 TABLE_PRIVILEGES
 TABLE_STATISTICS
 TRIGGERS
+THREAD_PRIORITIES
 create database information_schema;
 ERROR 42000: Access denied for user 'root'@'localhost' to database 'information_schema'
 use information_schema;
@@ -706,6 +711,7 @@ TABLE_CONSTRAINTS	SYSTEM VIEW
 TABLE_PRIVILEGES	SYSTEM VIEW
 TABLE_STATISTICS	SYSTEM VIEW
 TRIGGERS	SYSTEM VIEW
+THREAD_PRIORITIES	SYSTEM VIEW
 create table t1(a int);
 ERROR 42000: Access denied for user 'root'@'localhost' to database 'information_schema'
 use test;
@@ -721,6 +727,7 @@ TABLE_CONSTRAINTS
 TABLE_PRIVILEGES
 TABLE_STATISTICS
 TRIGGERS
+THREAD_PRIORITIES
 select table_name from tables where table_name='user';
 table_name
 user
@@ -957,7 +964,7 @@ table_schema IN ('mysql', 'INFORMATION_SCHEMA', 'test', 'mysqltest')
 AND table_name not like 'ndb%' AND table_name not like 'innodb_%'  AND table_name not like 'rocksdb_%'
 GROUP BY TABLE_SCHEMA;
 table_schema	count(*)
-information_schema	58
+information_schema	59
 mysql	27
 create table t1 (i int, j int);
 create trigger trg1 before insert on t1 for each row
@@ -1448,6 +1455,7 @@ TABLESPACES	information_schema.TABLESPACES	1
 TABLE_CONSTRAINTS	information_schema.TABLE_CONSTRAINTS	1
 TABLE_PRIVILEGES	information_schema.TABLE_PRIVILEGES	1
 TABLE_STATISTICS	information_schema.TABLE_STATISTICS	1
+THREAD_PRIORITIES	information_schema.THREAD_PRIORITIES	1
 TRANSACTION_LIST	information_schema.TRANSACTION_LIST	1
 TRIGGERS	information_schema.TRIGGERS	1
 USER_LATENCY_HISTOGRAMS	information_schema.USER_LATENCY_HISTOGRAMS	1

mysql-test/r/information_schema_db.result

@@ -63,6 +63,7 @@ COLUMN_STATISTICS
 DATABASE_APPLIED_HLC
 ADMISSION_CONTROL_QUEUE
 SQL_FINDINGS
+THREAD_PRIORITIES
 show tables from INFORMATION_SCHEMA like 'T%';
 Tables_in_information_schema (T%)
 TRANSACTION_LIST
@@ -72,6 +73,7 @@ TABLE_CONSTRAINTS
 TABLE_PRIVILEGES
 TABLE_STATISTICS
 TRIGGERS
+THREAD_PRIORITIES
 create database `inf%`;
 create database mbase;
 use `inf%`;

mysql-test/r/mysqld--help-notwin-profiling.result

@@ -2079,9 +2079,14 @@ The following options may be given as the first argument:
  --thread-handling=name 
  Define threads usage for handling queries, one of
  one-thread-per-connection, no-threads, loaded-dynamically
- --thread-nice-value[=name] 
- Input format is threadId:niceValue nice value range is
- -20 to 19
+ --thread-priority=# Set the priority of a thread. Changes the priority of the
+ current thread if set at the session level. Changes the
+ priority of all new threads if set at the global level.
+ The values are in the range -20 to 19, similar to nice.
+ --thread-priority-str[=name] 
+ Set the priority of a thread. The input format is
+ OSthreadId:PriValue. The priority values are in the range
+ -20 to 19, similar to nice.
  --thread-stack=#    The stack size for each thread
  --time-format=name  The TIME format (ignored)
  --timed-mutexes     Specify whether to time mutexes. Deprecated, has no
@@ -2785,7 +2790,8 @@ table-open-cache-instances 8
 tc-heuristic-recover COMMIT
 thread-cache-size 9
 thread-handling one-thread-per-connection
-thread-nice-value 
+thread-priority 0
+thread-priority-str 
 thread-stack 327680
 time-format %H:%i:%s
 timed-mutexes FALSE

mysql-test/r/mysqld--help-notwin.result

@@ -2077,9 +2077,14 @@ The following options may be given as the first argument:
  --thread-handling=name 
  Define threads usage for handling queries, one of
  one-thread-per-connection, no-threads, loaded-dynamically
- --thread-nice-value[=name] 
- Input format is threadId:niceValue nice value range is
- -20 to 19
+ --thread-priority=# Set the priority of a thread. Changes the priority of the
+ current thread if set at the session level. Changes the
+ priority of all new threads if set at the global level.
+ The values are in the range -20 to 19, similar to nice.
+ --thread-priority-str[=name] 
+ Set the priority of a thread. The input format is
+ OSthreadId:PriValue. The priority values are in the range
+ -20 to 19, similar to nice.
  --thread-stack=#    The stack size for each thread
  --time-format=name  The TIME format (ignored)
  --timed-mutexes     Specify whether to time mutexes. Deprecated, has no
@@ -2782,7 +2787,8 @@ table-open-cache-instances 8
 tc-heuristic-recover COMMIT
 thread-cache-size 9
 thread-handling one-thread-per-connection
-thread-nice-value 
+thread-priority 0
+thread-priority-str 
 thread-stack 327680
 time-format %H:%i:%s
 timed-mutexes FALSE

mysql-test/r/mysqlshow.result

@@ -169,6 +169,7 @@ DROP TABLE t1, t2;
 | TABLE_CONSTRAINTS                     |
 | TABLE_PRIVILEGES                      |
 | TABLE_STATISTICS                      |
+| THREAD_PRIORITIES                     |
 | TRANSACTION_LIST                      |
 | TRIGGERS                              |
 | USER_LATENCY_HISTOGRAMS               |
@@ -270,6 +271,7 @@ DROP TABLE t1, t2;
 | TABLE_CONSTRAINTS                     |
 | TABLE_PRIVILEGES                      |
 | TABLE_STATISTICS                      |
+| THREAD_PRIORITIES                     |
 | TRANSACTION_LIST                      |
 | TRIGGERS                              |
 | USER_LATENCY_HISTOGRAMS               |