【正文】 Software Reliabil ity at City University, London, and the Technical University in Plovdiv, Bulgaria. It allows one to run various client applications concurrently against diverse SQL servers which use a significant subset of the entrylevel SQL92 language. The testbed contains a wrapper for the SQL servers, implemented as a DCOM ponent, accessed by the client applications. Fig. 1 shows its architecture. The testbed was created to allow experiments with 3 functionally parable OTS SQL servers, Oracle , MS SQL , Interbase . The servers can run under any operating system for which there are versions of the products used。 ? various modes of concurrency control between the clients: ? Free mode, . unrestricted access to servers by all clients. The level of isolation between the transactions provided by the servers is set to “serialisable”, but no mechanism (. atomic broadcast) is implemented in the testbed to control the order in which the queries are delivered to the individual servers and hence executed by the servers. The clients are multithreaded, with a separate thread talking to each of the servers. ? Bottleneck mode, which imposes a very restrictive total order of the access by the clients to the server, with no concurrency between the clients. The threads representing the clients are synchronised (using critical sections) and the servers are supplied with only one transaction at a time. The next transaction (ing from any of the peting clients) is only initiated after the previous transaction is either mitted or rolled back。 ii) a simplified banking application, in which funds are being transferred between accounts under the invariant condition that the total amount of funds remains constant. This invariant allows a simple correctness check (“oracle”) for whether the overall series of transactions is processed correctly by the server(s). With the “warehouse” client application, a parison of the tables in the databases checks at predefined intervals whether the databases remain consistent, but no oracle exists to detect which of the servers has failed in case of disagreement. A third application is under development, based on the TPCC benchmark [9]. The testbed allows different configuration parameters to be changed such as: ? the number of clients and of queries submitted by each in an experiment。V activities – are either impossible or infeasible without costs parable to those of bespoke development. This situation may well change in the future, if customers with serious dependability requirements achieve more clout in their dealings with OTS ponent developers, but this possibility does not help system integrators who are in this kind of situation now. Fault tolerance may take multiple forms, ., additional (possibly purposebuilt but relatively simple) ponents performing protective wrapping, watchdog, monitor ing, auditing functions, to detect undesired behaviour of the OTS ponents, pre vent their producing serious consequences, and possibly effecting recovery of the ponents’ states。 外文資料 Software FaultTolerance with OfftheShelf SQL Servers P. Popov1, L. Strigini1, A. Kostov2, V. Mollov2, and D. Selensky2 1 Centre for Software Reliability, City University, London, UK {ptp, 2 Department of Computing, Technical University, Plovdiv, Bulgaria , Abstract:With offtheshelf software, software fault tolerance is almost the only means available for assuring better dependability than the offtheshelf software offers, without the much higher costs of bespoke development or extra Vamp。選擇后者可能是更有效的，但它是管理和正確實(shí)施更加修復(fù)和任何后續(xù)的升級(jí)，它必須在所有客戶端應(yīng)用程序的復(fù)制。查詢執(zhí)行期間，多個(gè)鎖可以交換服務(wù)器之間的線程訪問共享資源的競爭。另一種方法殺線程塊頂部 ?鏈也有其成本?？蛻舳瞬挥玫却肋h(yuǎn)會(huì)得到異常，可以回滾事 務(wù)，并鎖傳遞給其他客戶。我們已經(jīng)找到了另一種完全自動(dòng)化的解決方案，這種方案，可以改變舊版客戶端的情況下并包裝在一起。我們后來發(fā)現(xiàn)，微軟的 SQL服務(wù)器的故障（錯(cuò)誤＃ 56013）問題。對(duì)于每個(gè)詳細(xì)的事件日志做實(shí)驗(yàn)記錄，例如，作為發(fā)送的查詢，所提出的所有異常， ping響應(yīng)，查詢和響應(yīng)的時(shí)間與數(shù)據(jù)庫進(jìn)行比較。下一交易（來自任何競爭的客戶端）啟動(dòng)后，以前的事務(wù)被提交或回滾。由服務(wù)器提供的交易之間的隔離級(jí)別設(shè)置為 serialisable， 但沒有機(jī)制（如原子廣播）是在測試平臺(tái)實(shí)施控制查詢被傳遞到單個(gè)服務(wù)器。測試平臺(tái)選擇查詢類型和參數(shù)值， AC 盤帶用戶設(shè)置的概率分布。與“倉庫”的客戶端應(yīng)用程序，數(shù)據(jù)庫中的表進(jìn)行比較，檢查是否在預(yù)定的時(shí)間間隔里保持?jǐn)?shù)據(jù)庫一致，為了檢測服務(wù)器已在分歧的情況下失敗。圖 1 為它的架構(gòu)。必要性，因此，我們的解決方案是基于限制的客戶端和 SQL服務(wù)器（ S）之間的相互作用。包裝不正確的和潛在的 172。在 NSCP，每一個(gè)不同的“版本”應(yīng)該失敗干凈，使任何人都可以復(fù)制的產(chǎn)出作為系統(tǒng)的輸出使用。我們已經(jīng)開發(fā)了