Backport of:

-------------------------------------------------------------
revno: 2877
committer: Davi Arnaut <Davi.Arnaut@Sun.COM>
branch nick: 35164-6.0
timestamp: Wed 2008-10-15 19:53:18 -0300
message:
Bug#35164: Large number of invalid pthread_attr_setschedparam calls
Bug#37536: Thread scheduling causes performance degradation at low thread count
Bug#12702: Long queries take 100% of CPU and freeze other applications under Windows

The problem is that although having threads with different priorities
yields marginal improvements [1] in some platforms [2], relying on some
statically defined priorities (QUERY_PRIOR and WAIT_PRIOR) to play well
(or to work at all) with different scheduling practices and disciplines
is, at best, a shot in the dark as the meaning of priority values may
change depending on the scheduling policy set for the process.

Another problem is that increasing priorities can hurt other concurrent
(running on the same hardware) applications (such as AMP) by causing
starvation problems as MySQL threads will successively preempt lower
priority processes. This can be evidenced by Bug#12702.

The solution is to not change the threads priorities and rely on the
system scheduler to perform its job. This also enables a system admin
to increase or decrease the scheduling priority of the MySQL process,
if intended.

Furthermore, the internal wrappers and code for changing the priority
of threads is being removed as they are now unused and ancient.

1. Due to unintentional side effects. On Solaris this could artificially
help benchmarks as calling the priority changing syscall millions of
times is more beneficial than the actual setting of the priority.

2. Where it actually works. It has never worked on Linux as the default
scheduling policy SCHED_OTHER only accepts the static priority 0.


configure.in:
  Remove checks for functions that are not used anymore.
include/config-netware.h:
  Remove unused define.
include/my_pthread.h:
  Remove thread priority changing wrappers.
mysys/my_pthread.c:
  Remove thread priority changing wrappers. They do not work properly
  and their implementations were incorrectly protected by a check for
  HAVE_PTHREAD_SETSCHEDPARAM.
mysys/thr_alarm.c:
  Remove meaningless (100) increase of a thread priority.
sql/mysql_priv.h:
  Remove meaningless thread priority values.
sql/mysqld.cc:
  Don't change thread priorities.
sql/slave.cc:
  Don't change thread priorities.
sql/slave.h:
  Update function prototype.
sql/sql_parse.cc:
  Don't change thread priorities.
sql/sql_prepare.cc:
  Don't change thread priorities.
sql/unireg.h:
  Mark flag as obsolete.
storage/innobase/handler/ha_innodb.cc:
  Remove use of obsolete flag and associated behavior.
storage/innobase/include/srv0srv.h:
  Remove use of obsolete flag and associated variables.
storage/innobase/os/os0thread.c:
  Remove use of obsolete flag and associated behavior.
storage/innobase/srv/srv0srv.c:
  Remove use of obsolete flag and associated variables.

1 files changed, 0 insertions, 12 deletions

diff --git a/sql/sql_prepare.cc b/sql/sql_prepare.cc
index 168934206e5..d624c22f43a 100644
--- a/sql/sql_prepare.cc
+++ b/sql/sql_prepare.cc
@@ -2615,14 +2615,8 @@ void mysqld_stmt_fetch(THD *thd, char *packet, uint packet_length)
   thd->stmt_arena= stmt;
   thd->set_n_backup_statement(stmt, &stmt_backup);
 
-  if (!(specialflag & SPECIAL_NO_PRIOR))
-    my_pthread_setprio(pthread_self(), QUERY_PRIOR);
-
   cursor->fetch(num_rows);
 
-  if (!(specialflag & SPECIAL_NO_PRIOR))
-    my_pthread_setprio(pthread_self(), WAIT_PRIOR);
-
   if (!cursor->is_open())
   {
     stmt->close_cursor();
@@ -3386,14 +3380,8 @@ reexecute:
     thd->m_reprepare_observer = &reprepare_observer;
   }
 
-  if (!(specialflag & SPECIAL_NO_PRIOR))
-    my_pthread_setprio(pthread_self(),QUERY_PRIOR);
-
   error= execute(expanded_query, open_cursor) || thd->is_error();
 
-  if (!(specialflag & SPECIAL_NO_PRIOR))
-    my_pthread_setprio(pthread_self(), WAIT_PRIOR);
-
   thd->m_reprepare_observer= NULL;
 
   if (error && !thd->is_fatal_error && !thd->killed &&