MDEV-14638 - Replace trx_sys_t::rw_trx_set with LF_HASH

trx reference counter was updated under mutex and read without any
protection. This is both slow and unsafe. Use atomic operations for
reference counter accesses.

storage/innobase/include/row0vers.h

@@ -45,7 +45,7 @@ index record.
 @param[in]	rec	secondary index record
 @param[in]	index	secondary index
 @param[in]	offsets	rec_get_offsets(rec, index)
-@return	the active transaction; trx_release_reference() must be invoked
+@return	the active transaction; trx->release_reference() must be invoked
 @retval	NULL if the record was committed */
 trx_t*
 row_vers_impl_x_locked(

storage/innobase/include/trx0sys.h

@@ -598,7 +598,7 @@ public:
 
     With do_ref_count == true caller may dereference trx even if it is not
     holding lock_sys->mutex. Caller is responsible for calling
-    trx_release_reference() when it is done playing with trx.
+    trx->release_reference() when it is done playing with trx.
 
     Ideally this method should get caller rw_trx_hash_pins along with trx
     object as a parameter, similar to insert() and erase(). However most
@@ -646,7 +646,7 @@ public:
       if ((trx= element->trx))
       {
         if (do_ref_count)
-          trx_reference(trx);
+          trx->reference();
 #ifdef UNIV_DEBUG
         mutex_enter(&trx->mutex);
         ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE) ||

storage/innobase/include/trx0trx.h

@@ -532,26 +532,6 @@ void
 trx_set_rw_mode(
 	trx_t*		trx);
 
-/**
-Increase the reference count.
-@param trx Transaction that is being referenced */
-UNIV_INLINE
-void
-trx_reference(
-	trx_t*		trx);
-
-/**
-Release the transaction. Decrease the reference count.
-@param trx Transaction that is being released */
-UNIV_INLINE
-void
-trx_release_reference(
-	trx_t*		trx);
-
-/**
-Check if the transaction is being referenced. */
-#define trx_is_referenced(t)	((t)->n_ref > 0)
-
 /**
 @param[in] requestor	Transaction requesting the lock
 @param[in] holder	Transaction holding the lock
@@ -889,6 +869,19 @@ struct TrxVersion {
 typedef std::list<TrxVersion, ut_allocator<TrxVersion> > hit_list_t;
 
 struct trx_t {
+private:
+  /**
+    Count of references.
+
+    We can't release the locks nor commit the transaction until this reference
+    is 0. We can change the state to TRX_STATE_COMMITTED_IN_MEMORY to signify
+    that it is no longer "active".
+  */
+
+  int32_t n_ref;
+
+
+public:
 	TrxMutex	mutex;		/*!< Mutex protecting the fields
 					state and lock (except some fields
 					of lock, which are protected by
@@ -1235,14 +1228,6 @@ struct trx_t {
 	const char*	start_file;	/*!< Filename where it was started */
 #endif /* UNIV_DEBUG */
 
-	lint		n_ref;		/*!< Count of references, protected
-					by trx_t::mutex. We can't release the
-					locks nor commit the transaction until
-					this reference is 0.  We can change
-					the state to COMMITTED_IN_MEMORY to
-					signify that it is no longer
-					"active". */
-
 	/** Version of this instance. It is incremented each time the
 	instance is re-used in trx_start_low(). It is used to track
 	whether a transaction has been restarted since it was tagged
@@ -1311,6 +1296,33 @@ struct trx_t {
 		return(assign_temp_rseg());
 	}
 
+
+  bool is_referenced()
+  {
+    return my_atomic_load32_explicit(&n_ref, MY_MEMORY_ORDER_RELAXED) > 0;
+  }
+
+
+  void reference()
+  {
+#ifdef UNIV_DEBUG
+  int32_t old_n_ref=
+#endif
+    my_atomic_add32_explicit(&n_ref, 1, MY_MEMORY_ORDER_RELAXED);
+    ut_ad(old_n_ref >= 0);
+  }
+
+
+  void release_reference()
+  {
+#ifdef UNIV_DEBUG
+  int32_t old_n_ref=
+#endif
+    my_atomic_add32_explicit(&n_ref, -1, MY_MEMORY_ORDER_RELAXED);
+    ut_ad(old_n_ref > 0);
+  }
+
+
 private:
 	/** Assign a rollback segment for modifying temporary tables.
 	@return the assigned rollback segment */

storage/innobase/include/trx0trx.ic

@@ -213,34 +213,6 @@ ok:
 	trx->dict_operation = op;
 }
 
-/**
-Increase the reference count.
-@param trx Transaction that is being referenced */
-UNIV_INLINE void trx_reference(trx_t *trx)
-{
-  trx_mutex_enter(trx);
-  ut_ad(trx->n_ref >= 0);
-  ++trx->n_ref;
-  trx_mutex_exit(trx);
-}
-
-/**
-Release the transaction. Decrease the reference count.
-@param trx Transaction that is being released */
-UNIV_INLINE
-void
-trx_release_reference(
-	trx_t*		trx)
-{
-	trx_mutex_enter(trx);
-
-	ut_ad(trx->n_ref > 0);
-	--trx->n_ref;
-
-	trx_mutex_exit(trx);
-}
-
-
 /**
 @param trx		Get the active view for this transaction, if one exists
 @return the transaction's read view or NULL if one not assigned. */

storage/innobase/lock/lock0lock.cc

@@ -6813,7 +6813,7 @@ lock_rec_convert_impl_to_expl_for_trx(
 	trx_t*			trx,	/*!< in/out: active transaction */
 	ulint			heap_no)/*!< in: rec heap number to lock */
 {
-	ut_ad(trx_is_referenced(trx));
+	ut_ad(trx->is_referenced());
 	ut_ad(page_rec_is_leaf(rec));
 	ut_ad(!rec_is_default_row(rec, index));
 
@@ -6837,7 +6837,7 @@ lock_rec_convert_impl_to_expl_for_trx(
 
 	lock_mutex_exit();
 
-	trx_release_reference(trx);
+	trx->release_reference();
 
 	DEBUG_SYNC_C("after_lock_rec_convert_impl_to_expl_for_trx");
 }
@@ -6883,7 +6883,7 @@ lock_rec_convert_impl_to_expl(
 	if (trx != 0) {
 		ulint	heap_no = page_rec_get_heap_no(rec);
 
-		ut_ad(trx_is_referenced(trx));
+		ut_ad(trx->is_referenced());
 
 		/* If the transaction is still active and has no
 		explicit x-lock set on the record, set one for it.
@@ -7655,13 +7655,13 @@ lock_trx_release_locks(
 	trx->state = TRX_STATE_COMMITTED_IN_MEMORY;
 	/*--------------------------------------*/
 
-	if (trx_is_referenced(trx)) {
+	if (trx->is_referenced()) {
 
 		ut_a(release_lock);
 
 		lock_mutex_exit();
 
-		while (trx_is_referenced(trx)) {
+		while (trx->is_referenced()) {
 
 			trx_mutex_exit(trx);
 
@@ -7681,7 +7681,7 @@ lock_trx_release_locks(
 		trx_mutex_enter(trx);
 	}
 
-	ut_ad(!trx_is_referenced(trx));
+	ut_ad(!trx->is_referenced());
 
 	/* If the background thread trx_rollback_or_clean_recovered()
 	is still active then there is a chance that the rollback

storage/innobase/row/row0sel.cc

@@ -4982,7 +4982,7 @@ wrong_offs:
 					   trx, rec, index, offsets)) {
 				/* The record belongs to an active
 				transaction. We must acquire a lock. */
-				trx_release_reference(t);
+				t->release_reference();
 			} else {
 				/* The secondary index record does not
 				point to a delete-marked clustered index

storage/innobase/row/row0vers.cc

@@ -73,7 +73,7 @@ index record.
 @param[in]	index		secondary index
 @param[in]	offsets		rec_get_offsets(rec, index)
 @param[in,out]	mtr		mini-transaction
-@return	the active transaction; trx_release_reference() must be invoked
+@return	the active transaction; trx->release_reference() must be invoked
 @retval	NULL if the record was committed */
 UNIV_INLINE
 trx_t*
@@ -217,7 +217,7 @@ row_vers_impl_x_locked_low(
 				or updated, the leaf page record always is
 				created with a clear delete-mark flag.
 				(We never insert a delete-marked record.) */
-				trx_release_reference(trx);
+				trx->release_reference();
 				trx = 0;
 			}
 
@@ -328,7 +328,7 @@ result_check:
 			/* prev_version was the first version modified by
 			the trx_id transaction: no implicit x-lock */
 
-			trx_release_reference(trx);
+			trx->release_reference();
 			trx = 0;
 			break;
 		}
@@ -350,7 +350,7 @@ index record.
 @param[in]	rec	secondary index record
 @param[in]	index	secondary index
 @param[in]	offsets	rec_get_offsets(rec, index)
-@return	the active transaction; trx_release_reference() must be invoked
+@return	the active transaction; trx->release_reference() must be invoked
 @retval	NULL if the record was committed */
 trx_t*
 row_vers_impl_x_locked(
@@ -398,7 +398,7 @@ row_vers_impl_x_locked(
 				caller_trx, clust_rec, clust_index, rec, index,
 				offsets, &mtr);
 
-		ut_ad(trx == 0 || trx_is_referenced(trx));
+		ut_ad(trx == 0 || trx->is_referenced());
 	}
 
 	mtr_commit(&mtr);