MDEV-26356 preparation: Refactor purge_state

purge_coordinator_timer_callback(): Remove. We will have
purge_coordinator_timer invoke purge_coordinator_callback()
directly.

srv_master_callback(): Invoke srv_wake_purge_thread_if_not_active()
instead of purge_coordinator_timer_callback(). That is, we will
trigger purge_coordinator_callback() once per second if there is
any work to be done.

purge_state::do_purge(): Replaces srv_do_purge(),
purge_coordinator_callback_low(), and
purge_coordinator_timer_callback(). The static variables
inside srv_do_purge() were moved to purge_state data members.

storage/innobase/srv/srv0srv.cc

@@ -528,7 +528,14 @@ struct purge_coordinator_state
   /** Snapshot of the last history length before the purge call.*/
   uint32 m_history_length;
   Atomic_counter<int> m_running;
-  purge_coordinator_state() : m_history_length(), m_running(0) {}
+private:
+  ulint count;
+  ulint n_use_threads;
+  ulint n_threads;
+
+  inline void lazy_init();
+public:
+  inline void do_purge();
 };
 
 static purge_coordinator_state purge_state;
@@ -1329,7 +1336,6 @@ bool srv_any_background_activity()
 
 static void purge_worker_callback(void*);
 static void purge_coordinator_callback(void*);
-static void purge_coordinator_timer_callback(void*);
 
 static tpool::task_group purge_task_group;
 tpool::waitable_task purge_worker_task(purge_worker_callback, nullptr,
@@ -1621,24 +1627,25 @@ void srv_shutdown(bool ibuf_merge)
 /** The periodic master task controlling the server. */
 void srv_master_callback(void*)
 {
-	static ulint old_activity_count;
+  static ulint old_activity_count;
 
-	ut_a(srv_shutdown_state <= SRV_SHUTDOWN_INITIATED);
+  ut_a(srv_shutdown_state <= SRV_SHUTDOWN_INITIATED);
 
-	MONITOR_INC(MONITOR_MASTER_THREAD_SLEEP);
-	ut_d(srv_master_do_disabled_loop());
-	purge_coordinator_timer_callback(nullptr);
-	ulonglong counter_time = microsecond_interval_timer();
-	srv_sync_log_buffer_in_background();
-	MONITOR_INC_TIME_IN_MICRO_SECS(
-		MONITOR_SRV_LOG_FLUSH_MICROSECOND, counter_time);
+  MONITOR_INC(MONITOR_MASTER_THREAD_SLEEP);
+  ut_d(srv_master_do_disabled_loop());
+  if (!purge_state.m_running)
+    srv_wake_purge_thread_if_not_active();
+  ulonglong counter_time= microsecond_interval_timer();
+  srv_sync_log_buffer_in_background();
+  MONITOR_INC_TIME_IN_MICRO_SECS(MONITOR_SRV_LOG_FLUSH_MICROSECOND,
+				 counter_time);
 
-	if (srv_check_activity(&old_activity_count)) {
-		srv_master_do_active_tasks(counter_time);
-	} else {
-		srv_master_do_idle_tasks(counter_time);
-	}
-	srv_main_thread_op_info = "sleeping";
+  if (srv_check_activity(&old_activity_count))
+    srv_master_do_active_tasks(counter_time);
+  else
+    srv_master_do_idle_tasks(counter_time);
+
+  srv_main_thread_op_info= "sleeping";
 }
 
 /** @return whether purge should exit due to shutdown */
@@ -1711,86 +1718,88 @@ void srv_update_purge_thread_count(uint n)
 
 Atomic_counter<int> srv_purge_thread_count_changed;
 
-/** Do the actual purge operation.
-@param[in,out]	n_total_purged	total number of purged pages
-@return length of history list before the last purge batch. */
-static uint32_t srv_do_purge(ulint* n_total_purged)
+inline void purge_coordinator_state::do_purge()
 {
-	ulint		n_pages_purged;
+  ut_ad(!srv_read_only_mode);
+  lazy_init();
+  ut_ad(n_threads);
+  bool wakeup= false;
 
-	static ulint	count = 0;
-	static ulint	n_use_threads = 0;
-	static uint32_t	rseg_history_len = 0;
-	ulint		old_activity_count = srv_get_activity_count();
-	static ulint	n_threads = srv_n_purge_threads;
+  purge_coordinator_timer->disarm();
 
-	ut_a(n_threads > 0);
-	ut_ad(!srv_read_only_mode);
+  while (purge_sys.enabled() && !purge_sys.paused())
+  {
+loop:
+    wakeup= false;
+    const auto sigcount= m_running;
 
-	/* Purge until there are no more records to purge and there is
-	no change in configuration or server state. If the user has
-	configured more than one purge thread then we treat that as a
-	pool of threads and only use the extra threads if purge can't
-	keep up with updates. */
+    const auto old_activity_count= srv_sys.activity_count;
+    const auto history_size= trx_sys.history_size();
 
-	if (n_use_threads == 0) {
-		n_use_threads = n_threads;
-	}
+    if (UNIV_UNLIKELY(srv_purge_thread_count_changed))
+    {
+      /* Read the fresh value of srv_n_purge_threads, reset
+      the changed flag. Both are protected by purge_thread_count_mtx.
 
-	do {
-		if (UNIV_UNLIKELY(srv_purge_thread_count_changed)) {
-			/* Read the fresh value of srv_n_purge_threads, reset
-			the changed flag. Both variables are protected by
-			purge_thread_count_mtx.
-
-			This code does not run concurrently, it is executed
-			by a single purge_coordinator thread, and no races
-			involving srv_purge_thread_count_changed are possible.
-			*/
-
-			std::lock_guard<std::mutex> lk(purge_thread_count_mtx);
-			n_threads = n_use_threads = srv_n_purge_threads;
-			srv_purge_thread_count_changed = 0;
-		} else if (trx_sys.history_size_approx() > rseg_history_len
-			   || (srv_max_purge_lag > 0
-			       && rseg_history_len > srv_max_purge_lag)) {
-			/* History length is now longer than what it was
-			when we took the last snapshot. Use more threads. */
-
-			if (n_use_threads < n_threads) {
-				++n_use_threads;
-			}
+      This code does not run concurrently, it is executed
+      by a single purge_coordinator thread, and no races
+      involving srv_purge_thread_count_changed are possible. */
+      {
+        std::lock_guard<std::mutex> lk(purge_thread_count_mtx);
+        n_threads= n_use_threads= srv_n_purge_threads;
+        srv_purge_thread_count_changed= 0;
+      }
+    }
+    else if (history_size > m_history_length ||
+             (srv_max_purge_lag && m_history_length > srv_max_purge_lag))
+    {
+      /* dynamically adjust the purge thread based on redo log fill factor */
+      if (n_threads > n_use_threads)
+        ++n_use_threads;
+    }
+    else if (n_use_threads > 1 && old_activity_count == srv_sys.activity_count)
+      --n_use_threads;
 
-		} else if (srv_check_activity(&old_activity_count)
-			   && n_use_threads > 1) {
+    ut_ad(n_use_threads);
+    ut_ad(n_use_threads <= n_threads);
 
-			/* History length same or smaller since last snapshot,
-			use fewer threads. */
+    m_history_length= history_size;
 
-			--n_use_threads;
-		}
+    if (history_size &&
+        trx_purge(n_use_threads,
+                  !(++count % srv_purge_rseg_truncate_frequency) ||
+                  purge_sys.truncate.current))
+      continue;
 
-		/* Ensure that the purge threads are less than what
-		was configured. */
+    if (m_running == sigcount)
+    {
+      /* Purge was not woken up by srv_wake_purge_thread_if_not_active() */
 
-		ut_a(n_use_threads > 0);
-		ut_a(n_use_threads <= n_threads);
+      /* The magic number 5000 is an approximation for the case where we have
+      cached undo log records which prevent truncate of rollback segments. */
+      wakeup= history_size &&
+        (history_size >= 5000 ||
+         history_size != trx_sys.history_size_approx());
+      break;
+    }
+    else if (!trx_sys.history_exists())
+      break;
 
-		/* Take a snapshot of the history list before purge. */
-		if (!(rseg_history_len = trx_sys.history_size())) {
-			break;
-		}
+    if (!srv_purge_should_exit())
+      goto loop;
+  }
 
-		n_pages_purged = trx_purge(
-			n_use_threads,
-			!(++count % srv_purge_rseg_truncate_frequency)
-			|| purge_sys.truncate.current);
+  if (wakeup)
+    purge_coordinator_timer->set_time(10, 0);
 
-		*n_total_purged += n_pages_purged;
-	} while (n_pages_purged > 0 && !purge_sys.paused()
-		 && !srv_purge_should_exit());
+  m_running= 0;
+}
 
-	return(rseg_history_len);
+inline void purge_coordinator_state::lazy_init()
+{
+  if (n_threads)
+    return;
+  n_threads= n_use_threads= srv_n_purge_threads;
 }
 
 
@@ -1836,24 +1845,6 @@ static void release_thd(THD *thd, void *ctx)
 	set_current_thd(0);
 }
 
-
-/**
-  Called by timer when purge coordinator decides
-  to delay processing of purge records.
-*/
-static void purge_coordinator_timer_callback(void *)
-{
-  if (!purge_sys.enabled() || purge_sys.paused() || purge_state.m_running)
-    return;
-
-  /* The magic number 5000 is an approximation for the case where we have
-  cached undo log records which prevent truncate of the rollback segments. */
-  if (const auto history_size= trx_sys.history_size())
-    if (purge_state.m_history_length >= 5000 ||
-        purge_state.m_history_length != history_size)
-      srv_wake_purge_thread_if_not_active();
-}
-
 static void purge_worker_callback(void*)
 {
   ut_ad(!current_thd);
@@ -1866,57 +1857,19 @@ static void purge_worker_callback(void*)
   release_thd(thd,ctx);
 }
 
-static void purge_coordinator_callback_low()
-{
-  ulint n_total_purged= ULINT_UNDEFINED;
-  purge_state.m_history_length= 0;
-
-  if (!purge_sys.enabled() || purge_sys.paused())
-    return;
-  do
-  {
-    n_total_purged = 0;
-    int sigcount= purge_state.m_running;
-
-    purge_state.m_history_length= srv_do_purge(&n_total_purged);
-
-    /* Check if purge was woken by srv_wake_purge_thread_if_not_active() */
-
-    bool woken_during_purge= purge_state.m_running > sigcount;
-
-    /* If last purge batch processed less than 1 page and there is
-    still work to do, delay the next batch by 10ms. Unless
-    someone added work and woke us up. */
-    if (n_total_purged == 0)
-    {
-      if (trx_sys.history_size() == 0)
-        return;
-      if (!woken_during_purge)
-      {
-        /* Delay next purge round*/
-        purge_coordinator_timer->set_time(10, 0);
-        return;
-      }
-    }
-  }
-  while ((purge_sys.enabled() && !purge_sys.paused()) ||
-         !srv_purge_should_exit());
-}
-
 static void purge_coordinator_callback(void*)
 {
   void *ctx;
   THD *thd= acquire_thd(&ctx);
-  purge_coordinator_callback_low();
-  release_thd(thd,ctx);
-  purge_state.m_running= 0;
+  purge_state.do_purge();
+  release_thd(thd, ctx);
 }
 
 void srv_init_purge_tasks()
 {
   purge_create_background_thds(srv_n_purge_threads);
   purge_coordinator_timer= srv_thread_pool->create_timer
-    (purge_coordinator_timer_callback, nullptr);
+    (purge_coordinator_callback, nullptr);
 }
 
 static void srv_shutdown_purge_tasks()