DB Projects Help>> Database transaction and the ACID rules
The strategy of a collection purchase (or nuclear transaction) has developed as a way to help both a well recognized collection application behavior in a bad atmosphere where fails can occur every time, and restoration from a collision to a well recognized collection condition. A collection purchase is a model of operate, generally encapsulating a variety of businesses over a collection (e.g., examining a collection subject, composing, getting secure, etc.), an abstraction recognized in collection and also other techniques. Each purchase has well identified border with regards to which program/code accomplishments are involved in that purchase (determined by the transaction's designer via particular purchase commands). Every collection purchase obeys the following regulations (by service in the collection system; i.e., a collection application is developed to assurance them for the dealings it runs):
原子- Either the results of all or none of its businesses continue to be ("all or nothing" semantics) when a purchase is carried out (committed or aborted respectively). In other thoughts, to the outside community a dedicated purchase seems to be (by its results on the database) to be indivisible, nuclear, and an aborted purchase does not abandon results on the collection at all, as if never persisted.
一致性- Every purchase must abandon the collection in a regular (correct) condition, i.e., sustain the established reliability regulations of the collection (constraints upon and among the database's objects). A purchase must enhance a collection from one regular condition to another regular condition (however, it is the liability of the transaction's designer to develop sure that the purchase itself is appropriate, i.e., works effectively what it wants to accomplish (from the application's position of view) while the definite reliability regulations are made by the DBMS). Thus since a collection can be normally improved only by dealings, all the database's declares are regular. An aborted purchase does not modify the collection condition it has commenced from, as if it never persisted (atomicity above).
隔离- 交易不能彼此冲突（作为执行的最终结果）。此外，通常（取决于并发管理方法）不完善购买的结果甚至都不明显。给出孤独是并发管理的确定目标。
耐用性- Results of profitable (committed) dealings must continue to persist through fails (typically by documenting the transaction's results and it's develop occurrence in a non-volatile memory).
在时间里，核购买策略已延长到已经成为实际应用工作流但不是核的交易的交易。但是，这种增加的交易通常通常使用核交易作为要素。
数据库备份
A collection control system needs a particular technique, and this is one that is effective, particularly in small to medium-sized suppliers where there is not always the capability to individual the computer businesses assignments from those of the collection experts.
此技术以及一些更改也可以用于客户数据文件，例如系统数据文件Web服务器上的数据。
备份需要保证信息，还需要管理副本的可靠性和文章。例如，如果设计师无意间截断了桌子，那么如果其中没有信息包含信息，则一致地支持该桌子没有任何好处。
The best scenario for this copy technique is that the company should also have a copy web server that is a total identical of the web server.
在计划的完整记录副本之前，执行磁盘到盘副本是避免第二级问题，该问题允许记录复制灾难，并且仍然提供了在发生碰撞时绝对检索硬盘的方法。
日常备份的程序和过程
在Web服务器上运行收集可靠性检查。
Creation Collection家具单独发布到Web服务器上的磁盘。
The DBMS vendor supplied collection copy routine is run on the web server.
The DBMS example on the web server is shut down.
寒冷的一个副本ll the data, the DBMS example and the ripped out individual furniture is done onto tape on the web server.
The DBMS example on the web server is cut back online.
The individual released creation collection furniture are ripped to the copy web server using a file operating system command.
The furniture on the copy web server are truncated.
The furniture on the copy web server are then loaded from the individually released copy furniture on the copy web server.
Run collection reliability checks on the copy web server.
DBMS供应商提供的收集复制例程在复制Web服务器上运行。
复制Web服务器上的DBMS示例已关闭。
The cold copy of the copy web server is done.
复制Web服务器上的DBMS示例在线缩短。
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