MDEV-11026 Make InnoDB number of IO write/read threads dynamic

Resize the read/write slots, and recreate the io_context (for Linux libaio)

mysql-test/suite/sys_vars/r/innodb_file_io_threads_basic.result

@@ -8,16 +8,10 @@ COUNT(@@GLOBAL.innodb_write_io_threads)
 1
 1 Expected
 '#---------------------BS_STVARS_027_02----------------------#'
-SET @@GLOBAL.innodb_read_io_threads=1;
-ERROR HY000: Variable 'innodb_read_io_threads' is a read only variable
-Expected error 'Read only variable'
 SELECT COUNT(@@GLOBAL.innodb_read_io_threads);
 COUNT(@@GLOBAL.innodb_read_io_threads)
 1
 1 Expected
-SET @@GLOBAL.innodb_write_io_threads=1;
-ERROR HY000: Variable 'innodb_write_io_threads' is a read only variable
-Expected error 'Read only variable'
 SELECT COUNT(@@GLOBAL.innodb_write_io_threads);
 COUNT(@@GLOBAL.innodb_write_io_threads)
 1

mysql-test/suite/sys_vars/r/innodb_read_io_threads_basic.result

@@ -15,7 +15,15 @@ INNODB_READ_IO_THREADS	2
 select * from information_schema.session_variables where variable_name='innodb_read_io_threads';
 VARIABLE_NAME	VARIABLE_VALUE
 INNODB_READ_IO_THREADS	2
-set global innodb_read_io_threads=1;
-ERROR HY000: Variable 'innodb_read_io_threads' is a read only variable
+select @@innodb_read_io_threads into @n;
+set global innodb_read_io_threads = 1;
+select @@innodb_read_io_threads;
+@@innodb_read_io_threads
+1
+set global innodb_read_io_threads=64;
+select @@innodb_read_io_threads;
+@@innodb_read_io_threads
+64
 set session innodb_read_io_threads=1;
-ERROR HY000: Variable 'innodb_read_io_threads' is a read only variable
+ERROR HY000: Variable 'innodb_read_io_threads' is a GLOBAL variable and should be set with SET GLOBAL
+set global innodb_read_io_threads=@n;

mysql-test/suite/sys_vars/r/innodb_write_io_threads_basic.result

@@ -15,7 +15,13 @@ INNODB_WRITE_IO_THREADS	2
 select * from information_schema.session_variables where variable_name='innodb_write_io_threads';
 VARIABLE_NAME	VARIABLE_VALUE
 INNODB_WRITE_IO_THREADS	2
+select @@innodb_write_io_threads into @n;
 set global innodb_write_io_threads=1;
-ERROR HY000: Variable 'innodb_write_io_threads' is a read only variable
-set session innodb_write_io_threads=1;
-ERROR HY000: Variable 'innodb_write_io_threads' is a read only variable
+select @@innodb_write_io_threads;
+@@innodb_write_io_threads
+2
+set global innodb_write_io_threads=64;
+select @@innodb_write_io_threads;
+@@innodb_write_io_threads
+64
+set global innodb_write_io_threads=@n;

mysql-test/suite/sys_vars/r/sysvars_innodb.result

@@ -1349,7 +1349,7 @@ NUMERIC_MIN_VALUE	1
 NUMERIC_MAX_VALUE	64
 NUMERIC_BLOCK_SIZE	0
 ENUM_VALUE_LIST	NULL
-READ_ONLY	YES
+READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	INNODB_READ_ONLY
 SESSION_VALUE	NULL
@@ -1697,5 +1697,5 @@ NUMERIC_MIN_VALUE	2
 NUMERIC_MAX_VALUE	64
 NUMERIC_BLOCK_SIZE	0
 ENUM_VALUE_LIST	NULL
-READ_ONLY	YES
+READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED

mysql-test/suite/sys_vars/t/innodb_file_io_threads_basic.test

@@ -39,17 +39,10 @@ SELECT COUNT(@@GLOBAL.innodb_write_io_threads);
 #   Check if Value can set                                         #
 ####################################################################
 
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-SET @@GLOBAL.innodb_read_io_threads=1;
---echo Expected error 'Read only variable'
 
 SELECT COUNT(@@GLOBAL.innodb_read_io_threads);
 --echo 1 Expected
 
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-SET @@GLOBAL.innodb_write_io_threads=1;
---echo Expected error 'Read only variable'
-
 SELECT COUNT(@@GLOBAL.innodb_write_io_threads);
 --echo 1 Expected
 

mysql-test/suite/sys_vars/t/innodb_read_io_threads_basic.test

@@ -19,10 +19,18 @@ select * from information_schema.session_variables where variable_name='innodb_r
 --enable_warnings
 
 #
-# show that it's read-only
+# show that it's not read-only
 #
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-set global innodb_read_io_threads=1;
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
+select @@innodb_read_io_threads into @n;
+--disable_warnings
+set global innodb_read_io_threads = 1;
+--enable_warnings
+select @@innodb_read_io_threads;
+--disable_warnings
+set global innodb_read_io_threads=64;
+--enable_warnings
+select @@innodb_read_io_threads;
+--error ER_GLOBAL_VARIABLE
 set session innodb_read_io_threads=1;
+set global innodb_read_io_threads=@n;
 

mysql-test/suite/sys_vars/t/innodb_write_io_threads_basic.test

@@ -19,10 +19,18 @@ select * from information_schema.session_variables where variable_name='innodb_w
 --enable_warnings
 
 #
-# show that it's read-only
+# show that it's not read-only
 #
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
+select @@innodb_write_io_threads into @n;
+--disable_warnings
 set global innodb_write_io_threads=1;
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-set session innodb_write_io_threads=1;
+--enable_warnings
+select @@innodb_write_io_threads;
+--disable_warnings
+set global innodb_write_io_threads=64;
+--enable_warnings
+select @@innodb_write_io_threads;
+--disable_warnings
+set global innodb_write_io_threads=@n;
+--enable_warnings
 

storage/innobase/handler/ha_innodb.cc

@@ -19261,15 +19261,44 @@ static MYSQL_SYSVAR_BOOL(optimize_fulltext_only, innodb_optimize_fulltext_only,
   "Only optimize the Fulltext index of the table",
   NULL, NULL, FALSE);
 
+extern int os_aio_resize(ulint n_reader_threads, ulint n_writer_threads);
+static void innodb_update_io_thread_count(THD *thd,ulint n_read, ulint n_write)
+{
+  int res = os_aio_resize(n_read, n_write);
+  if (res)
+  {
+#ifndef __linux__
+    ut_ad(0);
+#else
+    ut_a(srv_use_native_aio);
+    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
+      ER_UNKNOWN_ERROR,
+      "Could not reserve max. number of concurrent ios."
+      "Increase the /proc/sys/fs/aio-max-nr to fix.");
+#endif
+  }
+}
+
+static void innodb_read_io_threads_update(THD* thd, struct st_mysql_sys_var*, void*, const void* save)
+{
+  srv_n_read_io_threads = *static_cast<const uint*>(save);
+  innodb_update_io_thread_count(thd, srv_n_read_io_threads, srv_n_write_io_threads);
+}
+static void innodb_write_io_threads_update(THD* thd, struct st_mysql_sys_var*, void*, const void* save)
+{
+  srv_n_write_io_threads = *static_cast<const uint*>(save);
+  innodb_update_io_thread_count(thd, srv_n_read_io_threads, srv_n_write_io_threads);
+}
+
 static MYSQL_SYSVAR_UINT(read_io_threads, srv_n_read_io_threads,
-  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
+  PLUGIN_VAR_RQCMDARG,
   "Number of background read I/O threads in InnoDB.",
-  NULL, NULL, 4, 1, 64, 0);
+  NULL, innodb_read_io_threads_update , 4, 1, 64, 0);
 
 static MYSQL_SYSVAR_UINT(write_io_threads, srv_n_write_io_threads,
-  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
+  PLUGIN_VAR_RQCMDARG,
   "Number of background write I/O threads in InnoDB.",
-  NULL, NULL, 4, 2, 64, 0);
+  NULL, innodb_write_io_threads_update, 4, 2, 64, 0);
 
 static MYSQL_SYSVAR_ULONG(force_recovery, srv_force_recovery,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,

storage/innobase/os/os0file.cc

@@ -106,6 +106,11 @@ public:
 	}
 
 	/* Wait for completions of all AIO operations */
+	void wait(std::unique_lock<std::mutex> &lk)
+	{
+		m_cache.wait(lk);
+	}
+
 	void wait()
 	{
 		m_cache.wait();
@@ -125,6 +130,24 @@ public:
 	{
 		wait();
 	}
+
+	std::mutex& mutex()
+	{
+		return m_cache.mutex();
+	}
+
+	void resize(int max_submitted_io, int max_callback_concurrency, std::unique_lock<std::mutex> &lk)
+	{
+		ut_a(lk.owns_lock());
+		m_cache.resize(max_submitted_io);
+		m_group.set_max_tasks(max_callback_concurrency);
+		m_max_aio = max_submitted_io;
+	}
+
+	tpool::task_group& task_group()
+	{
+		return m_group;
+	}
 };
 
 static std::unique_ptr<io_slots> read_slots;
@@ -3698,6 +3721,58 @@ disable:
 }
 
 
+/**
+Change reader or writer thread parameter on a running server.
+This includes resizing  the io slots, as we calculate
+number of outstanding IOs based on the these variables.
+
+It is trickier with when Linux AIO is involved (io_context
+needs to be recreated to account for different number of
+max_events). With Linux AIO, depending on fs-max-aio number
+and user and system wide max-aio limitation, this can fail.
+
+Otherwise, we just resize the slots, and allow for
+more concurrent threads via thread_group setting.
+
+@param[in] n_reader_threads - max number of concurrently
+  executing read callbacks
+@param[in] n_writer_thread - max number of cuncurrently
+  executing write callbacks
+@return 0 for success, !=0 for error.
+*/
+int os_aio_resize(ulint n_reader_threads, ulint n_writer_threads)
+{
+  /* Lock the slots, and wait until all current IOs finish.*/
+  std::unique_lock<std::mutex> lk_read(read_slots->mutex());
+  std::unique_lock<std::mutex> lk_write(write_slots->mutex());
+
+  read_slots->wait(lk_read);
+  write_slots->wait(lk_write);
+
+  /* Now, all IOs have finished and no new ones can start, due to locks. */
+  int max_read_events= int(n_reader_threads * OS_AIO_N_PENDING_IOS_PER_THREAD);
+  int max_write_events= int(n_writer_threads * OS_AIO_N_PENDING_IOS_PER_THREAD);
+  int events= max_read_events + max_write_events;
+
+  /** Do the Linux AIO dance (this will try to create a new
+  io context with changed max_events ,etc*/
+
+  if (int ret= srv_thread_pool->reconfigure_aio(srv_use_native_aio, events))
+  {
+    /** Do the best effort. We can't change the parallel io number,
+    but we still can adjust the number of concurrent completion handlers.*/
+    read_slots->task_group().set_max_tasks(static_cast<int>(n_reader_threads));
+    write_slots->task_group().set_max_tasks(static_cast<int>(n_writer_threads));
+    return ret;
+  }
+
+  /* Allocation succeeded, resize the slots*/
+  read_slots->resize(max_read_events, static_cast<int>(n_reader_threads), lk_read);
+  write_slots->resize(max_write_events, static_cast<int>(n_writer_threads), lk_write);
+
+  return 0;
+}
+
 void os_aio_free()
 {
   srv_thread_pool->disable_aio();

tpool/tpool.h

@@ -231,6 +231,20 @@ public:
       m_aio.reset(create_simulated_aio(this));
     return !m_aio ? -1 : 0;
   }
+
+  int reconfigure_aio(bool use_native_aio, int max_io)
+  {
+    assert(m_aio);
+    if (use_native_aio)
+    {
+      auto new_aio = create_native_aio(max_io);
+      if (!new_aio)
+        return -1;
+      m_aio.reset(new_aio);
+    }
+    return 0;
+  }
+
   void disable_aio()
   {
     m_aio.reset();

tpool/tpool_structs.h

@@ -94,6 +94,10 @@ public:
     return ret;
   }
 
+  std::mutex& mutex()
+  {
+    return m_mtx;
+  }
 
   void put(T *ele)
   {
@@ -112,20 +116,38 @@ public:
     return ele >= &m_base[0] && ele <= &m_base[m_base.size() -1];
   }
 
-  /* Wait until cache is full.*/
-  void wait()
-  {
-    std::unique_lock<std::mutex> lk(m_mtx);
-    m_waiters++;
-    while(!is_full())
-      m_cv.wait(lk);
-    m_waiters--;
-  }
 
   TPOOL_SUPPRESS_TSAN size_t size()
   {
     return m_cache.size();
   }
+
+  /** Wait until cache is full
+  @param[in] lk -  lock for the cache mutex
+  (which can be obtained with mutex()) */
+  void wait(std::unique_lock<std::mutex> &lk)
+  {
+    m_waiters++;
+    while (!is_full())
+      m_cv.wait(lk);
+    m_waiters--;
+  }
+
+  /* Wait until cache is full.*/
+  void wait()
+  {
+    std::unique_lock<std::mutex> lk(m_mtx);
+    wait(lk);
+  }
+
+  void resize(size_t count)
+  {
+    assert(is_full());
+    m_base.resize(count);
+    m_cache.resize(count);
+    for (size_t i = 0; i < count; i++)
+      m_cache[i] = &m_base[i];
+  }
 };