trx0undo.h, trx0undo.c, trx0trx.c:

  Update an obsolete comment about trx commit: we can no longer call trx_undo_update_cleanup_by_discard(), and actually, the idea to call it was erroneous, it cannot work

innobase/include/trx0undo.h

@@ -251,20 +251,6 @@ trx_undo_update_cleanup(
 	page_t*	undo_page,	/* in: update undo log header page,
 				x-latched */
 	mtr_t*	mtr);		/* in: mtr */
-/**************************************************************************
-Discards an undo log and puts the segment to the list of cached update undo
-log segments. This optimized function is called if there is no need to
-keep the update undo log because there exist no read views and the transaction
-made no delete markings, which would make purge necessary. We restrict this
-to undo logs of size 1 to make things simpler. */
-
-dulint
-trx_undo_update_cleanup_by_discard(
-/*===============================*/
-			/* out: log sequence number at which mtr is
-			committed */	
-	trx_t*	trx,	/* in: trx owning the update undo log */
-	mtr_t*	mtr);	/* in: mtr */
 /**********************************************************************
 Frees or caches an insert undo log after a transaction commit or rollback.
 Knowledge of inserts is not needed after a commit or rollback, therefore

innobase/trx/trx0trx.c

@@ -701,11 +701,13 @@ trx_commit_off_kernel(
 				TRX_SYS_MYSQL_MASTER_LOG_INFO, &mtr);
 		}
 				
-		/* If we did not take the shortcut, the following call
-		commits the mini-transaction, making the whole transaction
-		committed in the file-based world at this log sequence number;
-		otherwise, we get the commit lsn from the call of
-		trx_undo_update_cleanup_by_discard above.
+		/* The following call commits the mini-transaction, making the
+		whole transaction committed in the file-based world, at this
+		log sequence number. The transaction becomes 'durable' when
+		we write the log to disk, but in the logical sense the commit
+		in the file-based data structures (undo logs etc.) happens
+		here.
+
 		NOTE that transaction numbers, which are assigned only to
 		transactions with an update undo log, do not necessarily come
 		in exactly the same order as commit lsn's, if the transactions

innobase/trx/trx0undo.c

@@ -1673,56 +1673,6 @@ trx_undo_update_cleanup(
 	}
 }
 
-/**************************************************************************
-Discards an undo log and puts the segment to the list of cached update undo
-log segments. This optimized function is called if there is no need to keep
-the update undo log because there exist no read views and the transaction
-made no delete markings, which would make purge necessary. We restrict this
-to undo logs of size 1 to make things simpler. */
-
-dulint
-trx_undo_update_cleanup_by_discard(
-/*===============================*/
-			/* out: log sequence number at which mtr is
-			committed */	
-	trx_t*	trx,	/* in: trx owning the update undo log */
-	mtr_t*	mtr)	/* in: mtr */
-{
-	trx_rseg_t*	rseg;
-	trx_undo_t*	undo;
-	page_t*		undo_page;
-	
-	undo = trx->update_undo;
-	rseg = trx->rseg;
-
-#ifdef UNIV_SYNC_DEBUG
-	ut_ad(mutex_own(&(rseg->mutex)));
-	ut_ad(mutex_own(&kernel_mutex));
-#endif /* UNIV_SYNC_DEBUG */
-	ut_ad(undo->size == 1);
-	ut_ad(undo->del_marks == FALSE);	
-	ut_ad(UT_LIST_GET_LEN(trx_sys->view_list) == 1);
-	
-	/* NOTE: we must hold the kernel mutex, because we must prevent
-	creation of new read views before mtr gets committed! */
-
-	undo_page = trx_undo_page_get(undo->space, undo->hdr_page_no, mtr);
-
-	trx_undo_discard_latest_update_undo(undo_page, mtr);
-
-	undo->state = TRX_UNDO_CACHED;
-
-	UT_LIST_REMOVE(undo_list, rseg->update_undo_list, undo);
-
-	trx->update_undo = NULL;
-
-	UT_LIST_ADD_FIRST(undo_list, rseg->update_undo_cached, undo);
-
-	mtr_commit(mtr);
-	
-	return(mtr->end_lsn);
-}
-
 /**********************************************************************
 Frees or caches an insert undo log after a transaction commit or rollback.
 Knowledge of inserts is not needed after a commit or rollback, therefore