MDEV-15914: Remove trx_undo_t::empty

Use the value trx_undo_t::top_undo_no == IB_ID_MAX for indicating
that an undo log is empty.

storage/innobase/include/trx0undo.h

@@ -370,8 +370,6 @@ struct trx_undo_t {
 					top_page_no during a rollback */
 	ulint		size;		/*!< current size in pages */
 	/*-----------------------------*/
-	ulint		empty;		/*!< TRUE if the stack of undo log
-					records is currently empty */
 	ulint		top_page_no;	/*!< page number where the latest undo
 					log record was catenated; during
 					rollback the page from which the latest
@@ -379,11 +377,16 @@ struct trx_undo_t {
 	ulint		top_offset;	/*!< offset of the latest undo record,
 					i.e., the topmost element in the undo
 					log if we think of it as a stack */
-	undo_no_t	top_undo_no;	/*!< undo number of the latest record */
+	undo_no_t	top_undo_no;	/*!< undo number of the latest record
+					(IB_ID_MAX if the undo log is empty) */
 	buf_block_t*	guess_block;	/*!< guess for the buffer block where
 					the top page might reside */
 	ulint		withdraw_clock;	/*!< the withdraw clock value of the
 					buffer pool when guess_block was stored */
+
+	/** @return whether the undo log is empty */
+	bool empty() const { return top_undo_no == IB_ID_MAX; }
+
 	/*-----------------------------*/
 	UT_LIST_NODE_T(trx_undo_t) undo_list;
 					/*!< undo log objects in the rollback

storage/innobase/trx/trx0rec.cc

@@ -1916,11 +1916,11 @@ trx_undo_report_rename(trx_t* trx, const dict_table_t* table)
 			if (ulint offset = trx_undo_page_report_rename(
 				    trx, table, block, &mtr)) {
 				undo->withdraw_clock = buf_withdraw_clock;
-				undo->empty = FALSE;
 				undo->top_page_no = undo->last_page_no;
 				undo->top_offset  = offset;
 				undo->top_undo_no = trx->undo_no++;
 				undo->guess_block = block;
+				ut_ad(!undo->empty());
 
 				err = DB_SUCCESS;
 				break;
@@ -2012,7 +2012,7 @@ trx_undo_report_row_operation(
 	trx_undo_t*	undo	= *pundo;
 
 	ut_ad((err == DB_SUCCESS) == (undo_block != NULL));
-	if (undo_block == NULL) {
+	if (UNIV_UNLIKELY(undo_block == NULL)) {
 		goto err_exit;
 	}
 
@@ -2062,11 +2062,11 @@ trx_undo_report_row_operation(
 			undo->withdraw_clock = buf_withdraw_clock;
 			mtr_commit(&mtr);
 
-			undo->empty = FALSE;
 			undo->top_page_no = undo_block->page.id.page_no();
 			undo->top_offset  = offset;
 			undo->top_undo_no = trx->undo_no++;
 			undo->guess_block = undo_block;
+			ut_ad(!undo->empty());
 
 			mutex_exit(&trx->undo_mutex);
 
@@ -2111,7 +2111,7 @@ trx_undo_report_row_operation(
 
 		DBUG_EXECUTE_IF("ib_err_ins_undo_page_add_failure",
 				undo_block = NULL;);
-	} while (undo_block != NULL);
+	} while (UNIV_LIKELY(undo_block != NULL));
 
 	ib_errf(trx->mysql_thd, IB_LOG_LEVEL_ERROR,
 		DB_OUT_OF_FILE_SPACE,

storage/innobase/trx/trx0roll.cc

@@ -946,8 +946,8 @@ trx_roll_pop_top_rec(
 		true, mtr);
 
 	if (prev_rec == NULL) {
-
-		undo->empty = TRUE;
+		undo->top_undo_no = IB_ID_MAX;
+		ut_ad(undo->empty());
 	} else {
 		page_t*	prev_rec_page = page_align(prev_rec);
 
@@ -959,6 +959,7 @@ trx_roll_pop_top_rec(
 		undo->top_page_no = page_get_page_no(prev_rec_page);
 		undo->top_offset  = prev_rec - prev_rec_page;
 		undo->top_undo_no = trx_undo_rec_get_undo_no(prev_rec);
+		ut_ad(!undo->empty());
 	}
 
 	return(undo_page + offset);
@@ -985,19 +986,19 @@ trx_roll_pop_top_rec_of_trx(trx_t* trx, roll_ptr_t* roll_ptr, mem_heap_t* heap)
 	trx_undo_t*	temp	= trx->rsegs.m_noredo.undo;
 	const undo_no_t	limit	= trx->roll_limit;
 
-	ut_ad(!insert || !update || insert->empty || update->empty
+	ut_ad(!insert || !update || insert->empty() || update->empty()
 	      || insert->top_undo_no != update->top_undo_no);
-	ut_ad(!insert || !temp || insert->empty || temp->empty
+	ut_ad(!insert || !temp || insert->empty() || temp->empty()
 	      || insert->top_undo_no != temp->top_undo_no);
-	ut_ad(!update || !temp || update->empty || temp->empty
+	ut_ad(!update || !temp || update->empty() || temp->empty()
 	      || update->top_undo_no != temp->top_undo_no);
 
 	if (UNIV_LIKELY_NULL(insert)
-	    && !insert->empty && limit <= insert->top_undo_no) {
+	    && !insert->empty() && limit <= insert->top_undo_no) {
 		undo = insert;
 	}
 
-	if (update && !update->empty && update->top_undo_no >= limit) {
+	if (update && !update->empty() && update->top_undo_no >= limit) {
 		if (!undo) {
 			undo = update;
 		} else if (undo->top_undo_no < update->top_undo_no) {
@@ -1005,7 +1006,7 @@ trx_roll_pop_top_rec_of_trx(trx_t* trx, roll_ptr_t* roll_ptr, mem_heap_t* heap)
 		}
 	}
 
-	if (temp && !temp->empty && temp->top_undo_no >= limit) {
+	if (temp && !temp->empty() && temp->top_undo_no >= limit) {
 		if (!undo) {
 			undo = temp;
 		} else if (undo->top_undo_no < temp->top_undo_no) {
@@ -1024,7 +1025,7 @@ trx_roll_pop_top_rec_of_trx(trx_t* trx, roll_ptr_t* roll_ptr, mem_heap_t* heap)
 		return(NULL);
 	}
 
-	ut_ad(!undo->empty);
+	ut_ad(!undo->empty());
 	ut_ad(limit <= undo->top_undo_no);
 
 	*roll_ptr = trx_undo_build_roll_ptr(

storage/innobase/trx/trx0trx.cc

@@ -571,8 +571,7 @@ trx_resurrect_table_locks(
 	      trx_state_eq(trx, TRX_STATE_PREPARED));
 	ut_ad(undo->rseg == trx->rsegs.m_redo.rseg);
 
-	if (undo->empty) {
-
+	if (undo->empty()) {
 		return;
 	}
 
@@ -687,11 +686,7 @@ static void trx_resurrect(trx_undo_t *undo, trx_rseg_t *rseg,
   else
     trx->rsegs.m_redo.undo= undo;
 
-  if (!undo->empty)
-  {
   trx->undo_no= undo->top_undo_no + 1;
-  }
-
   trx->rsegs.m_redo.rseg= rseg;
   /*
     For transactions with active data will not have rseg size = 1
@@ -784,8 +779,7 @@ trx_lists_init_at_db_start()
 				ut_ad(trx->rsegs.m_redo.rseg->trx_ref_count);
 
 				trx->rsegs.m_redo.undo = undo;
-				if (!undo->empty
-				    && undo->top_undo_no >= trx->undo_no) {
+				if (undo->top_undo_no >= trx->undo_no) {
 					if (trx_state_eq(trx,
 							 TRX_STATE_ACTIVE)) {
 						rows_to_undo -= trx->undo_no;

storage/innobase/trx/trx0undo.cc

@@ -1150,13 +1150,14 @@ trx_undo_mem_create_at_db_start(trx_rseg_t* rseg, ulint id, ulint page_no,
 		page_t* last_page = trx_undo_page_get(
 			page_id_t(rseg->space->id, undo->last_page_no), &mtr);
 
-		const trx_undo_rec_t*	rec = trx_undo_page_get_last_rec(
-			last_page, page_no, offset);
-
-		undo->empty = !rec;
-		if (rec) {
+		if (const trx_undo_rec_t* rec = trx_undo_page_get_last_rec(
+			    last_page, page_no, offset)) {
 			undo->top_offset = rec - last_page;
 			undo->top_undo_no = trx_undo_rec_get_undo_no(rec);
+			ut_ad(!undo->empty());
+		} else {
+			undo->top_undo_no = IB_ID_MAX;
+			ut_ad(undo->empty());
 		}
 	}
 
@@ -1217,10 +1218,11 @@ trx_undo_mem_create(
 	undo->last_page_no = page_no;
 	undo->size = 1;
 
-	undo->empty = TRUE;
+	undo->top_undo_no = IB_ID_MAX;
 	undo->top_page_no = page_no;
 	undo->guess_block = NULL;
 	undo->withdraw_clock = 0;
+	ut_ad(undo->empty());
 
 	return(undo);
 }
@@ -1248,7 +1250,8 @@ trx_undo_mem_init_for_reuse(
 	undo->dict_operation = FALSE;
 
 	undo->hdr_offset = offset;
-	undo->empty = TRUE;
+	undo->top_undo_no = IB_ID_MAX;
+	ut_ad(undo->empty());
 }
 
 /** Create an undo log.