Is a schema stability sch - s lock . in this case , serializability is no longer guaranteed 唯一采用的鎖是架構(gòu)穩(wěn)定性鎖( sch - s鎖) 。
Serializability may not be implemented using only row - level locks ; there must be another mechanism that prevents a newly inserted row from becoming visible to a transaction that has already executed a query that would return the row 如果僅僅通過“行級(jí)鎖”是無法實(shí)現(xiàn)事務(wù)序列化的,必須通過其他機(jī)制保證新插入的數(shù)據(jù)不會(huì)被剛執(zhí)行查詢操作的事務(wù)訪問到。
This is referred to as serializability because it results in the ability to reload the starting data and replay a series of transactions to end up with the data in the same state it was in after the original transactions were performed 這稱為可串行性,因?yàn)樗軌蛑匦卵b載起始數(shù)據(jù),并且重播一系列事務(wù),以使數(shù)據(jù)結(jié)束時(shí)的狀態(tài)與原始事務(wù)執(zhí)行的狀態(tài)相同。
But at present , there seem to be much deficiencies on the correctness and reliability of workflow and it can not meet the practical needs very well . in this paper , we introduce some transactional properties to workflow and put forward a nested workflow model with transactional characteristics . this model includes nested tasks and dependencies between the tasks , and it is provided with some atm properties such as relaxed isolation and atomicity . further more , we discuss the execution mechanism , system recovery and error handling of workflow on the base of the transactional characteristics . by defining consistency unit and execution atomic unit , we loosen the failure atomicity , serializability of concurrent worflow and isolation between tasks , thus , workflow meets the needs of the application semantics more flexiblly with high correctness and reliability 這個(gè)模型包含嵌套任務(wù)和任務(wù)間的依賴,并具有高級(jí)事務(wù)模型的一些屬性,比如松散的隔離性和原子性。我們又進(jìn)一步在這個(gè)模型的基礎(chǔ)上利用這些事務(wù)性質(zhì)提出了有關(guān)工作流的執(zhí)行機(jī)制、系統(tǒng)恢復(fù)和錯(cuò)誤處理等問題的解決方法。通過定義一致性單元和執(zhí)行單元放松了事務(wù)的失敗原子性、并發(fā)工作流的可串行化要求以及任務(wù)間的隔離性,使工作流在具有高可靠性和正確性的前提下更靈活地滿足實(shí)際應(yīng)用語義的要求。