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1、Four short words sum up what has lifted most successful individuals above the crowd: a little bit more.-author-datemysql数据库英文文献mysql数据库英文文献mysql数据库英文文献及翻译 MySQL architecture is best understood in the context of its history. Thus, the two are discussed in the same chapter.MySQL History MySQL history

2、goes back to 1979 when Monty Widenius, working for a small companycalled TcX, created a reporting tool written in BASIC that ran on a 4 Mhzcomputer with 16 KB RAM. Over time, the tool was rewritten in C and ported to run on Unix. It was still just a low-level storage engine with a reporting front en

3、d. The tool was known by the name of Unireg. Working under the adverse conditions of little computational resources, and perhaps building on his God-given talent,Monty developed a habit and ability to write very efficient code naturally. He also developed, or perhaps was gifted from the start,with a

4、n unusually acute vision of what needed to be done to the code to make it useful in future developmentwithout knowing in advance much detail about what that future development would be. In addition to the above, with TcX being a very small company and Monty being one of the owners, he had a lot of s

5、ay in what happened to his code. While there are perhaps a good number of programmers out there with Montys talent and ability, for a number of reasons, few get to carry their code around for more than 20 years. Monty did. Montys work, talents, and ownership of the code provided a foundation upon wh

6、ich the Miracle of MySQL could be built. Some time in the 1990s, TcX customers began to push for an SQL interface to their data. Several possibilities were considered. One was to load it into a commercial database.Monty was not satisfied with the speed. He tried borrowing mSQL code for the SQL part

7、and integrating it with his low-level storage engine. That did not work well,either. Then came the classic move of a talented,driven programmer: “Ive had enough of those tools that somebody else wrote that dont work! Im writing my own!” Thus in May of 1996 MySQL version 1.0 was released to a limited

8、 group, followed by a public release in October 1996 of version 3.11.1. The initial public release provided only a binary distribution for Solaris. A month later, the source and the Linux binary were released. In the next two years, MySQL was ported to a number of other operating systems as the feat

9、ure set gradually increased. MySQL was originally released under a special license that allowed commercial use to those who were not redistributing it with their software. Special licenses were available for sale to those who wanted to bundle it with their product. Additionally, commercial support w

10、as also being sold. This provided TcX with some revenue to justify the further development of MySQL,although the purpose of its original creation had already been fulfilled. During this period MySQL progressed to version 3.22. It supported a decent subset of the SQL language, had an optimizer a lot

11、more sophisticated than one would expect could possibly be written by one person, was extremely fast, and was very stable.Numerous APIs were contributed, so one could write a client in pretty much any existing programming language. However, it still lacked support for transactions,subqueries, foreig

12、n keys, stored procedures, and views. The locking happened only at a table level, which in some cases could slow it down to a grinding halt. Some programmers unable to get around its limitations still considered it a toy, while others were more than happy to dump their Oracle or SQL Server in favor

13、of MySQL, and deal with the limitations in their code in exchange for improvement in performance and licensing cost savings. Around 19992000 a separate company named MySQL AB was established. It hired several developers and established a partnership with Sleepycat to provide an SQL interface for the

14、 Berkeley DB data files. Since Berkeley DB had transaction capabilities,this would give MySQL support for transactions, which it previously lacked.After some changes in the code in preparation for integrating Berkeley DB,version 3.23 was released. Although the MySQL developers could never work out a

15、ll the quirks of the Berkeley DB interface and the Berkeley DB tables were never stable, the effort was not wasted.As a result, MySQL source became equipped with hooks to add any type of storage engine, including a transactional one. By April of 2000, with 原文请找腾讯3249114六维-论文.网,ISAM, was reworked and

16、 released as MyISAM. Among a number of improvements,full-text search capabilities were now supported. A short-lived partnership with NuSphere to add Gemini, a transactional engine with row-level locking, ended in a lawsuit toward the end of 2001. However, around the same time, Heikki Tuuri approache

17、d MySQL AB with a proposal to integrate his own storage engine,InnoDB, which was also capable of transactions and row-level locking. Heikkis contribution integrated much more smoothly with the new table handler interface already polished off by the Berkeley DB integration efforts. The MySQL/InnoDB c

18、ombination became version 4.0, and was released as alpha in October of 2001. By early 2002 the MySQL/InnoDB combo was stable and instantly took MySQL to another level. Version 4.0 was finally declared production stable in March 2003. It might be worthy of mention that the version number change was n

19、ot caused by the addition of InnoDB. MySQL developers have always viewed InnoDB as an important addition, but by no means something that they completely depend on for success.Back then, and even now, the addition of a new storage engine is not likely to be celebrated with a version number change. In

20、 fact, compared to previous versions,not much was added in version 4.0. Perhaps the most significant addition was the query cache, which greatly improved performance of a large number of applications.Replication code on the slave was rewritten to use two threads: one for network I/O from the master,

21、 and the other to process the updates. Some improvements were added to the optimizer. The 1506mysql数据库英文文献及翻译client/server protocol became SSL-capable. Version 4.1 was released as alpha in April of 2003, and was declared beta in June of 2004. Unlike version 4.0, it added a number of significant impr

22、ovements. Perhaps the most significant was subqueries, a feature long-awaited by many users. Spatial indexing support was added to the MyISAM storage engine. Unicode support was implemented. The client/server protocol saw a number of changes. It was made more secure against attacks, and supported pr

23、epared statements. In parallel with the alpha version of 4.1, work progressed on yet another development branch: version 5.0, which would add stored procedures, server-side cursors,triggers, views, XA transactions, significant improvements in the query optimizer,and a number of other features. The d

24、ecision to create a separate development branch was made because MySQL developers felt that it would take a long time to stabilize 4.1 if, on top of all the new features that they were adding to it, they had to deal with the stored procedures. Version 5.0 was finally released as alpha in December 20

25、03. For a while this created quite a bit of confusionthere were two branches in the alpha stage. Eventually 4.1 stabilized (October 2004), and the confusion was resolved. Version 5.0 stabilized a year later, in October of 2005. The first alpha release of 5.1 followed in November 2005, which added a

26、number of improvements, some of which are table data partitioning, row-based replication,event scheduler, and a standardized plug-in API that facilitates the integration of new storage engines and other plug-ins. At this point, MySQL is being actively developed. 5.0 is currently the stable version,w

27、hile 5.1 is in beta and should soon become stable. New features at this point go into version 5.2.MySQL Architecture For the large part, MySQL architecture defies a formal definition or specification.When most of the code was originally written, it was not done to be a part of some great system in t

28、he future, but rather to solve some very specific problems. However,it was written so well and with enough insight that it reached the point where there were enough quality pieces to assemble a database server.Core Modules I make an attempt in this section to identify the core modules in the system.

29、 However,let me add a disclaimer that this is only an attempt to formalize what exists.MySQL developers rarely think in those terms. Rather, they tend to think of files,directories, classes, structures, and functions. It is much more common to hear “This happens in mi_open( )” than to hear “This hap

30、pens on the MyISAM storage engine level.” MySQL developers know the code so well that they are able to think conceptually on the level of functions, structures, and classes. They will probably find the abstractions in this section rather useless. However, it would be helpful to a person used to thin

31、king in terms of modules and managers. With regard to MySQL, I use the term “module” rather loosely. Unlike what one would typically call a module, in many cases it is not something you can easily pull out and replace with another implementation. The code from one module might be spread across sever

32、al files, and you often find the code from several different modules in the same file. This is particularly true of the older code. The newer code tends to fit into the pattern of modules better. So in our definition, a module is a piece of code that logically belongs together in some way, and perfo

33、rms a certain critical function in User Authentication Module Access Control Module Parser Command Dispatcher Query Cache Module Optimizer Table Manager Table Modification Modules Table Maintenance Module Status Reporting Module Abstracted Storage Engine Interface (Table Handler) Storage Engine Impl

34、ementations (MyISAM, InnoDB, MEMORY, Berkeley DB) Logging Module Replication Master Module Replication Slave Module Client/Server Protocol API Low-Level Network I/O API Core APIInteraction of the Core Modules When the server is started on the command line, the Initialization Module takes control.It

35、parses the configuration file and the command-line arguments, allocates global memory buffers, initializes global variables and structures, loads the access control tables, and performs a number of other initialization tasks. Once the initialization job is complete, the Initialization Module passes

36、control to the Connection Manager, which starts listening for connections from clients in a loop.mysql数据库英文文献及翻译 When a client connects to the database server, the Connection Manager performs a number of low-level network protocol tasks and then passes control to the Thread Manager, which in turn su

37、pplies a thread to handle the connection (which from now on will be referred to as the Connection Thread). The Connection Thread might be created anew, or retrieved from the thread cache and called to active duty. Once the Connection Thread receives control, it first invokes the User Authentication

38、Module.The credentials of the connecting user are verified, and the client may now issue requests. The Connection Thread passes the request data to the Command Dispatcher. Some requests, known in the MySQL code terminology as commands, can be accommodated by the Command Dispatcher directly, while mo

39、re complex ones need to be redirected to another module. A typical command may request the server to run a query, change the active database, report the status, send a continuous dump of the replication updates, close the connection, or perform some other operation. In MySQL server terminology, ther

40、e are two types of client requests: a query and a command. A query is anything that has to go through the parser. A command is a request that can be executed without the need to invoke the parser. We will use the term query in the context of MySQL internals. Thus, not only a SELECT but also a DELETE

41、 or INSERT in our terminology would be called a query. What we would call a query is sometimes called an SQL statement. If full query logging is enabled, the Command Dispatcher will ask the Logging Module to log the query or the command to the plain-text log prior to the dispatch. Thus in the full l

42、ogging configuration all queries will be logged, even the ones that are not syntactically correct and will never be executed, immediately returning an error. The Command Dispatcher forwards queries to the Parser through the Query Cache Module. The Query Cache Module checks whether the query is of th

43、e type that can be cached, and if there exists a previously computed cached result that is still valid.In the case of a hit, the execution is short-circuited at this point, the cached result is returned to the user, and the Connection Thread receives control and is now ready to process another comma

44、nd. If the Query Cache Module reports a miss, the query goes to the Parser, which will make a decision on how to transfer control based on the query type. One can identify the following modules that could continue from that point: the Optimizer, the Table Modification Module, the Table Maintenance M

45、odule, the Replication Module, and the Status Reporting Module. Select queries are forwarded to the Optimizer; updates, inserts, deletes, and table-creation and schema-altering queries go to the respective Table Modification Modules; queries that check, repair, update key statistics, or defragment t

46、he table go to the Table Maintenance module;queries related to replication go to the Replication Module; and status requests go to the Status Reporting Module. There also exist a number of Table Modification Modules: Delete Module, Create Module, Update Module, Insert Module, and Alter Module. At th

47、is point, each of the modules that will receive control from the Parser passes the list of tables involved in the query to the Access Control Module and then, upon success,to the Table Manager, which opens the tables and acquires the necessary locks.Now the table operation module is ready to proceed

48、 with its specific task and will issue a number of requests to the Abstracted Storage Engine Module for low-level operations such as inserting or updating a record, retrieving the records based on a key value, or performing an operation on the table level, such as repairing it or updating the index

49、statistics. The Abstracted Storage Engine Module will automatically translate the calls to the corresponding methods of the specific Storage Engine Module via object polymorphism.In other words, when dealing with a Storage Engine object, the caller thinks it isthe caller does not need to be aware of the exact object type of the Storage Engine object. As