And we take that in consideration because we also know that’s very cultural thing. We understand that.
我们也考虑到了这一点，这是不同文化造成的，我们也能理解。
But we’re also here because we know that over the years, despite all we have in common, the United States and Muslim communities around the world too often fell victim to mutual mistrust.
但是，我们今天在此聚会也是因为我们知道，尽管我们有如此之多的共同之处，多年来美国和世界各地的穆斯林社区经常由于缺乏互信而遭遇不幸。
But we're also here because we know that over the years, despite all we have in common, the United States and Muslim communities around the world too often fell victim to mutual mistrust.
然而，咱们今天在此聚会也是因为咱们晓得，只管咱们有如此之多的独特之处，多年来美国跟世界各地的穆斯林社区常常因为缺乏互信而遭受可怜。
This is a very strong focus group because we also know end-user behavior.
这是个非常强的焦点小组 ，因为我们同样知道终端用户行为。
Because we also know that when the king returns, he will bring us the thing.
因为我们都知道，当王者归来的时候，他会带来戒指。
We also play for them because we know that if their support will be always greater, we will do great things.
我想，好的比赛大概可以赢得他们更多的支持，这种支持反过来也更能激励我们更好地比赛。
You will be warned when you try to cheat but we also have many other surprises because we know how much you love surprises.
您将被警告当您尝试欺骗但我们也有其他许多惊喜，因为我们知道有多少你所爱的惊喜。
I am really annoyed because I know we also helped France to go through.
我真的很苦恼，因为我知道我们也帮助法国出线了。
Not only so, but we also rejoice in our sufferings, because we know that suffering produces perseverance.
不但如此，在患难中，我们仍然喜乐，因为我们知道患难培养忍耐。
Well, if we fear men because marriage also need to know more, please direct line with the site specialists to communicate fear.
好了，如果大家对男人婚前恐惧症的原因还需要了解更多，请直接在线与本站恐惧症专家进行沟通。
But we also say thank you because we want the other person to know we value what they’ve done for us and, maybe, encourage them to help us again in the future.
但我们跟别人说谢谢是因为我们想其他人知道我们珍惜他们为我们所做的一切，或许，鼓励他们在未来继续帮助我们。
And you can reduce also the side effects, which is very important because we know that the death rate is mainly higher when people are not put early on treatment.
治疗中的副作用也可以减轻。这很重要，因为我们知道死亡率高主要是由于感染者没有得到初期治疗。
You also know how to write dialogues, because we often use dialogues in class.
你们也知道怎能样写对话，因为我们上课经常用对话。
In addition to facilitating our method, this new scope also adds value because the requirement becomes a statement of everything we need to know over time about the essential need that it describes.
除了使我们的方法更容易之外，这个新的范围也是有价值的，因为这样的需求变成了在整个过程中我们需要了解的所有基本需求的详细叙述。
But then they also know the full end hasn't come because we don't see the Kingdom of God around us.
但他们也知道，完全的末日尚未到来,因为还没有看到天国降临。
We also know that op is a scalar variable because it is prefixed with the $.
我们还知道op是标量变量，因为它的前缀是 $。
Chinese people also prefer to deal with people we know and trust, because we hardly trust people who we do not know.
同样，中国人也是很倾向于同认识或者信任的人打交道，因为我们很难信任陌生人。
"Unlike previous studies, we also took into account whether the vegetables were cooked or raw because we know that cooking can substantially decrease the amount of isothiocyanates, " he continued.
“与以往的研究不同，我们还考虑了蔬菜的生熟，因为我们知道，烹调可以大大减少异硫氰酸酯的量， ”他继续说。
Because we know that this is a command, but also that we should observe.
因为我们知道这是命令，也是我们应该遵守的。
We know he was a keen observer because he was also an author.
我们之所以知晓他是个热衷的观察者，是因为他同时也是一个作家。
Finally, we still obediently walked inside. because we know that this is a command, but also that we should observe.
最后我们还是乖乖走进去。因为我们知道这是命令，也是我们应该遵守的。
I also know that we have tension here m2g and the tension must be m2 g because the object is not being accelerated.
我还知道，此时张力是这样的,大小为,因为物体没有加速。
We also know he had to let Cotto win, because I mean who else is Pacquiao going to fight?
我们知道他得让库托赢，要不然帕奎奥跟谁打？
We know that, and we will try to win also because we have a game on hand.
我们知道这情况，我们将努力获胜，而且我们还少赛一场。
"This is a boring job, " Muras was stroked toward the wall tomb ofKlaette, said, "Because we do not know when it will come, but also did not know where it will appear.
“这是一个枯燥的工作，”穆拉斯朝着正在抚摸墓室墙壁的科莱特说，“因为我们根本不知道它什么时候会来，也根本不知道它会出现在哪里。
Professor Marcelin: I think this is a good idea because we know the nucleoside and nucleotide analogs are sublimitation and also you got your own limitations.
Marcelin教授：我认为这是个好办法，因为我们知道核苷类药物是次限制的，而每个人会有自己的限制。
Professor Marcelin: I think this is a good idea because we know the nucleoside and nucleotide analogs are sublimitation and also you got your own limitations.
Marcelin教授：我认为这是个好办法，因为我们知道核苷类药物是次限制的，而每个人会有自己的限制。
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也因为这样，所以要特别注意他们上厕所的时候，有没有确实的大便和小便了。
These are the metals of coins and jewelry, not only because of their comparative rarity and beauty but also because of this chemical inertness.
这些金属是制造硬币和珠宝的金属，不只是因为它们的相对稀缺和漂亮，而且还因为化学惰性。
"I believe so because of the new constitution and the organic act that is about to pass into law and also because of this national anti-corruption strategy," said Professor Pakdee.
他说：“我相信会是这样，因为新的宪法以及这个即将通过的有机法律，另外也因为这个全国性的反腐败战略。
Also because of this, she's the wedding after the baptism of time, but still fresh, by everybody.
也正因为如此，她的那身婚纱经过时间的洗礼，却仍记忆犹新，受到大家的追捧。
His leg also because of this delicacy suffered an injury bloodily, does Luo Daquan ask Cheng Yimei wishes to marry Chen Ziming?
他的一条腿也因此而鲜血淋淋地受了伤，罗大全问程伊妹愿嫁陈子明吗？
This is Sanya's honor. And it's also because of this, Sanya starts to be on the way to the world.
这是三亚人民的骄傲，也正因为这样，三亚开始走向世界。
Also because of this, the risk assessment of mobile payment system is extremely essential and has the practical significance.
因此，对移动支付系统进行科学的风险评估是非常有必要和具有现实意义的。
Also because of this, the relevantnational laws and regulations have clearly defined that enterprises should carry outsafety training for new staff in accordance with the law.
也正因为如此，国家相关法律法规有明确规定企业应当依法开展新进员工安全培训工作。
He seldom stayed at home, and was always busy with his friends' and neighbors' business, and also because of this, Mom and Dad always quarreled with each other.
他很少待在家，而且总是忙于他的朋友和邻居的生意，以及因为这，妈妈和爸爸总是和彼此吵架。
Just let him get up, but also because of this cause he killed in a dream alone, the fact there was alone is not common the loss of life.
才让他暴富起来，但也因为这个造成他在梦中杀害独自一个人后，事实就有独自一个人不平常失去生命。 不过接二连三的旧梦再现，却导致一块儿连环凶杀案的发生！
Because the girl is his relatives, but also because of this girl, had died a year ago, he personally attended the funeral and saw the girl was buried in the grave.
因为这个姑娘是他的亲戚，还因为，这个姑娘，一年前已经死了，他亲自参加了葬礼，看见姑娘被埋进了坟墓。
Meanwhile, Andre is about to become a prisoner of the memory of Superman, but also because of this "academic gate" scandal has been an unprecedented challenge.
与此同时，即将沦为阶下囚的安德烈的超人记忆力，也因为这一“学历门”丑闻而遭到了前所未有的质疑。
Write a file on the Su Mian father's death and the letter group, but also because of this, Su Mian to apply to the letter group undercover, or wanted to find out his father's murderer.
卷宗上写着苏眠父亲的死和字母团有关，也是因为此，苏眠申请去字母团做卧底，想要找出还是自己父亲的真凶。
It is known by its reliability which earns thousands of consumers' compliments, also because of this, we have best after-sale system.
本公司向来以产品耐用性而闻名，赢得了广大消费者的恳定和青睐。本公司为消费者提供优越的售后服务。
Angeline: Actually, this is a conceptual album, incorporating the flavours of the Middle East and Love. Also, because of this album, we've increased our knowledge of the River Nile.
妮妮：其实这是一张概念专辑，它融合了中东与爱情的风味，也因为这张专辑，让我们对尼罗河有了更进一步的了解。
Due to advocating this kind of Platonic love, Andersen could not advance from this foundation all the time, and also positively because of this, he never marr…
由于崇尚这种柏拉图式的爱情，安徒生始终无法在精神恋爱的基础上再进一步，也正缘于此，他终生未娶。
Not only because I don't think the evidence supports such a sweeping conclusion, but also because of the pressure this puts on our kids.
因为我认为不仅证据不足以形成这么个结论，而且这个结论会给我们的孩子带来压力。
I also feel that because of this, many girls rush ahead and like the first guy that gives them attention.
我还感觉，正是因为这个原因，许多女孩子会迫不及待地喜欢上第一个来追求她们的男性。
Reporter: Do we know cruel dispatch rolled out travel of a " to experience the activity of division " also is adjusted because of this this year?
记者：今年我们知道酷讯推出了一个“旅游体验师”的活动也因为这个调整吗？
Also because feel this variety of earnestness, she just decides to quit, because she doesn't ambition to damage his heart.
也正是因为感觉到这种真挚，她才决定离开，因为她不想伤他的心。
Another, chou Jiabao and ex-wife and its daughter often have contact, in this disharmonious family environment, yu Xiaojiao often also hates the man because of this avoid.
另一头，仇家宝和前妻及其女儿常有来往，在本就不和谐的家庭环境中，于小娇也常常因此忌恨丈夫。 婆媳大战谁会是最后的赢家？
Also can't because of this, the extended other buying and selling?
也不能因为这个，延伸其他的买卖啊？
So I hope you will be able to help me find this sort of employment, not only because I need the money, but also because this type of job would give me an opportunity to improve my ability.
故希望阁下能鼎力相助谋此类工作，不仅是因为本人目前手头拮据，而且我相信此类工作有助于我工作能力的提高。
When abdomen one every day rise greatly inconvenience is meeting some this also because of the person different but actually oneself feel not bad look so cumber some without others.
等到肚子一天天的大起来，不方便是会有的，这个也因人而异，但其实自己感觉还好的，没有别人看起来那么粗笨。
Many industrial outside public figures also join in this industry because of the bloom of the automobile industry.
汽车行业的火爆，引发了很多业外人士也加入到这个行业中。
Also, it is just because of this kind of special function that helps add everlasting energy to model education.
正是因为榜样教育的这一独特功能使其保持了长盛不衰的生命力。
There're a lot of Disney themes as Donald Duck and Minnie Mouse. There's also a rabbit because, of course, this is in Chinese year of the rabbit, so they've done a particularly good trade in that.
许多服饰都是以迪斯尼人物比如唐老鸭和米老鼠作为主题，还有一只兔子，因为今年是中国的兔年，兔子装在市场上尤其大卖。
There're a lot of Disney themes as Donald Duck and Minnie Mouse. There's also a rabbit because, of course, this is in Chinese year of the rabbit, so they've done a particularly good trade in that.
许多服饰都是以迪斯尼人物比如唐老鸭和米老鼠作为主题，还有一只兔子，因为今年是中国的兔年，兔子装在市场上尤其大卖。
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请问您想要如何调整此模块？
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感谢您的反馈，我们会尽快进行适当修改！Grid Computing in Oracle Database 10g
On the path toward this grand vision of grid computing, companies need real solutions to support their incremental moves toward a more flexible and more productive IT architecture. The Oracle Database 10g family of software products implements much of the core grid technology to get companies started. And Oracle delivers this grid computing functionality in the context of holistic enterprise architecture, providing a robust security infrastructure, centralized management, intuitive, powerful development tools, and universal access. Oracle Database 10g includes:
Oracle Database 10g
Oracle Application Server 10g
Oracle Enterprise Manager 10g
Oracle Collaboration Suite 10g
Although the grid features of Oracle 10g span all of the products listed above, this discussion will focus on the grid computing capabilities of Oracle Database 10g.
Server Virtualization. Oracle Real Application Clusters 10g (RAC) enable a single database to run across multiple clustered nodes in a grid, pooling the processing resources of several standard machines. Oracle is uniquely flexible in its ability to provision workload across machines because it is the only database technology that does not require data to be partitioned and distributed along with the work. Oracle 10g Release 2 software includes enhancements for balancing connections across RAC instances, based on policies.
Storage Virtualization. The Oracle Automatic Storage Management (ASM) feature of Oracle Database 10g provides a virtualization layer between the database and storage so that multiple disks can be treated as a single disk group and disks can be dynamically added or removed while keeping databases online. Existing data will automatically be spread across available disks for performance and utilization optimization. In Oracle 10g Release 2, ASM supports multiple databases, which could be at different software version levels, accessing the same storage pool.
Grid Management. Because grid computing pools together multiple servers and disks and allocates them to multiple purposes, it becomes more important that individual resources are largely self-managing and that other management functions are centralized.
The Grid Control feature of Oracle Enterprise Manager 10g provides a single console to manage multiple systems together as a logical group. Grid Control manages provisioning of nodes in the grid with the appropriate full stack of software and enables configurations and security settings to be maintained centrally for groups of systems.
Another aspect to grid management is managing user identities in a way that is both highly secure and easy to maintain. Oracle Identity Management 10g includes an LDAP-compliant directory with delegated administration and now, in Release 2, federated identity management so that single sign-on capabilities can be securely shared across security domains. Oracle Identity Management 10g closely adheres to grid principles by utilizing a central point for applications to authenticate users - the single sign-on server - while, behind the scenes, distributing control of identities via delegation and federation to optimize maintainability and overall operation of the system.
Standard Web Services Support. In addition to the robust web services support in Oracle Application Server 10g, Oracle database 10g can publish and consume web services. DML and DDL operations can be exposed as web services, and functions within the database can make a web service appear as a SQL row source, enabling use of powerful SQL tools to analyze web service data in conjunction with relational and non-relational data.
Oracle Enterprise Manager 10g enhances Oracle's support for service oriented architectures by monitoring and managing web services and any other administrator-defined services, tracking end-to-end performance and performing root cause analysis of problems encountered.
Data Provisioning. Information starts with data, which must be provisioned wherever consumers need it. For example, users may be geographically distributed, and fast data access may be more important for these users than access to an identical resource. In these cases, data must be shared between systems, either in bulk or near real time. Oracle's bulk data movement technologies include Transportable Tablespaces and Data Pump.
For more fine-grained data sharing, the Oracle Streams feature of Oracle Database 10g captures database transaction changes and propagates them, thus keeping two or more database copies in sync as updates are applied. It also unifies traditionally distinct data sharing mechanisms, such as message queuing, replication, events, data warehouse loading, notifications and publish/subscribe, into a single technology.
Centralized Data Management. Oracle Database 10g manages all types of structured, semi-structured and unstructured information, representing, maintaining and querying each in its own optimal way while providing common access to all via SQL and XML Query. Along with traditional relational database structures, Oracle natively implements OLAP cubes, standard XML structures, geographic spatial data and unlimited sized file management, thus virtualizing information representation. Combining these information types enables connections between disparate types of information to be made as readily as new connections are made with traditional relational data.
Metadata Management. Oracle Warehouse Builder is more than a traditional batch ETL tool for creating warehouses. It enforces rules to achieve data quality, does fuzzy matching to automatically overcome data inconsistency, and uses statistical analysis to infer data profiles. With Oracle 10g Release 2, its metadata management capabilities are extended from scheduled data pulls to handle a transaction-time data push from an Oracle database implementing the Oracle Streams feature.
Oracle's series of enterprise data hub products (for example, Oracle Customer Data Hub) provide real-time synchronization of operational information sources so that companies can have a single source of truth while retaining separate systems and separate applications, which may include a combination of packaged, legacy and custom applications. In addition to the data cleansing and scheduling mechanisms, Oracle also provides a well-formed schema, established from years of experience building enterprise applications, for certain common types of information, such as customer, financial, and product information.
Metadata Inference. Joining the Oracle 10g software family is the new Oracle Enterprise Search product. Oracle Enterprise Search 10g crawls all information sources in the enterprise, whether public or secure, including e-mail servers, document management servers, file systems, web sites, databases and applications, then returns information from all of the most relevant sources for a given search query. This crawl and index process uses a series of heuristics specific to each data source to infer metadata about all enterprise information that is used to return the most relevant results to any query.
Overview of Application Architecture
There are two common ways to architect a database: client/server or multitier. As internet computing becomes more prevalent in computing environments, many database management systems are moving to a multitier environment.
Client/Server Architecture
Multiprocessing uses more than one processor for a set of related jobs. Distributed processing reduces the load on a single processor by allowing different processors to concentrate on a subset of related tasks, thus improving the performance and capabilities of the system as a whole.
An Oracle database system can easily take advantage of distributed processing by using its client/server architecture. In this architecture, the database system is divided into two parts: a front-end or a client, and a back-end or a server.
The Client
The client is a database application that initiates a request for an operation to be performed on the database server. It requests, processes, and presents data managed by the server. The client workstation can be optimized for its job. For example, it might not need large disk capacity, or it might benefit from graphic capabilities.
Often, the client runs on a different computer than the database server, generally on a PC. Many clients can simultaneously run against one server.
The Server
The server runs Oracle software and handles the functions required for concurrent, shared data access. The server receives and processes the SQL and PL/SQL statements that originate from client applications. The computer that manages the server can be optimized for its duties. For example, it can have large disk capacity and fast processors.
Multitier Architecture: Application Servers
A multitier architecture has the following components:
A client or initiator process that starts an operation
One or more application servers that perform parts of the operation. An application server provides access to the data for the client and performs some of the query processing, thus removing some of the load from the database server. It can serve as an interface between clients and multiple database servers, including providing an additional level of security.
An end or database server that stores most of the data used in the operation
This architecture enables use of an application server to do the following:
Validate the credentials of a client, such as a Web browser
Connect to an Oracle database server
Perform the requested operation on behalf of the client
If proxy authentication is being used, then the identity of the client is maintained throughout all tiers of the connection.
Overview of Physical Database Structures
The following sections explain the physical database structures of an Oracle database, including datafiles, redo log files, and control files.
Every Oracle database has one or more physical datafiles. The datafiles contain all the database data. The data of logical database structures, such as tables and indexes, is physically stored in the datafiles allocated for a database.
The characteristics of datafiles are:
A datafile can be associated with only one database.
Datafiles can have certain characteristics set to let them automatically extend when the database runs out of space.
One or more datafiles form a logical unit of database storage called a tablespace.
Data in a datafile is read, as needed, during normal database operation and stored in the memory cache of Oracle. For example, assume that a user wants to access some data in a table of a database. If the requested information is not already in the memory cache for the database, then it is read from the appropriate datafiles and stored in memory.
Modified or new data is not necessarily written to a datafile immediately. To reduce the amount of disk access and to increase performance, data is pooled in memory and written to the appropriate datafiles all at once, as determined by the
background process.
Control Files
Every Oracle database has a control file. A control file contains entries that specify the physical structure of the database. For example, it contains the following information:
Database name
Names and locations of datafiles and redo log files
Time stamp of database creation
Oracle can multiplex the control file, that is, simultaneously maintain a number of identical control file copies, to protect against a failure involving the control file.
Every time an
of an Oracle database is started, its control file identifies the database and redo log files that must be opened for database operation to proceed. If the physical makeup of the database is altered (for example, if a new datafile or redo log file is created), then the control file is automatically modified by Oracle to reflect the change. A control file is also used in database recovery.
Redo Log Files
Every Oracle database has a set of two or more redo log files. The set of redo log files is collectively known as the redo log for the database. A redo log is made up of redo entries (also called redo records).
The primary function of the redo log is to record all changes made to data. If a failure prevents modified data from being permanently written to the datafiles, then the changes can be obtained from the redo log, so work is never lost.
To protect against a failure involving the redo log itself, Oracle allows a multiplexed redo log so that two or more copies of the redo log can be maintained on different disks.
The information in a redo log file is used only to recover the database from a system or media failure that prevents database data from being written to the datafiles. For example, if an unexpected power outage terminates database operation, then data in memory cannot be written to the datafiles, and the data is lost. However, lost data can be recovered when the database is opened, after power is restored. By applying the information in the most recent redo log files to the database datafiles, Oracle restores the database to the time at which the power failure occurred.
The process of applying the redo log during a recovery operation is called rolling forward.
Archive Log Files
You can enable automatic archiving of the redo log. Oracle automatically archives log files when the database is in ARCHIVELOG mode.
Parameter Files
Parameter files contain a list of configuration parameters for that instance and database.
Oracle recommends that you create a server parameter file (SPFILE) as a dynamic means of maintaining initialization parameters. A server parameter file lets you store and manage your initialization parameters persistently in a server-side disk file.
Alert and Trace Log Files
Each server and background process can write to an associated trace file. When an internal error is detected by a process, it dumps information about the error to its trace file. Some of the information written to a trace file is intended for the database administrator, while other information is for Oracle Support Services. Trace file information is also used to tune applications and instances.
The alert file, or alert log, is a special trace file. The alert log of a database is a chronological log of messages and errors.
Backup Files
To restore a file is to replace it with a backup file. Typically, you restore a file when a media failure or user error has damaged or deleted the original file.
User-managed backup and recovery requires you to actually restore backup files before you can perform a trial recovery of the backups.
Server-managed backup and recovery manages the backup process, such as scheduling of backups, as well as the recovery process, such as applying the correct backup file when recovery is needed.
Overview of Logical Database Structures
The logical storage structures, including data blocks, extents, and segments, enable Oracle to have fine-grained control of disk space use.
Tablespaces
A database is divided into logical storage units called tablespaces, which group related logical structures together. For example, tablespaces commonly group together all application objects to simplify some administrative operations.
Each database is logically divided into one or more tablespaces. One or more datafiles are explicitly created for each tablespace to physically store the data of all logical structures in a tablespace. The combined size of the datafiles in a tablespace is the total storage capacity of the tablespace.
Every Oracle database contains a SYSTEM tablespace and a SYSAUX tablespace. Oracle creates them automatically when the database is created. The system default is to create a smallfile tablespace, which is the traditional type of Oracle tablespace. The SYSTEM and SYSAUX tablespaces are created as smallfile tablespaces.
Oracle also lets you create bigfile tablespaces. This allows Oracle Database to contain tablespaces made up of single large files rather than numerous smaller ones. This lets Oracle Database utilize the ability of 64-bit systems to create and manage ultralarge files. The consequence of this is that Oracle Database can now scale up to 8 exabytes in size. With Oracle-managed files, bigfile tablespaces make datafiles completely transparent for users. In other words, you can perform operations on tablespaces, rather than the underlying datafiles.
Online and Offline Tablespaces
A tablespace can be online (accessible) or offline (not accessible). A tablespace is generally online, so that users can access the information in the tablespace. However, sometimes a tablespace is taken offline to make a portion of the database unavailable while allowing normal access to the remainder of the database. This makes many administrative tasks easier to perform.
Oracle Data Blocks
At the finest level of granularity, Oracle database data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk. The standard block size is specified by the DB_BLOCK_SIZE initialization parameter. In addition, you can specify up to five other block sizes. A database uses and allocates free database space in Oracle data blocks.
The next level of logical database space is an extent. An extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
Above extents, the level of logical database storage is a segment. A segment is a set of extents allocated for a certain logical structure. The following table describes the different types of segments.
Oracle dynamically allocates space when the existing extents of a segment become full. In other words, when the extents of a segment are full, Oracle allocates another extent for that segment. Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk.
Overview of Schemas and Common Schema Objects
A schema is a collection of database objects. A schema is owned by a database user and has the same name as that user. Schema objects are the logical structures that directly refer to the database's data. Schema objects include structures like s, s, and es. (There is no relationship between a tablespace and a schema. Objects in the same schema can be in different tablespaces, and a tablespace can hold objects from different schemas.)
Some of the most common schema objects are defined in the following section.
Tables are the basic unit of data storage in an Oracle database. Database tables hold all user-accessible data. Each table has s and s. A table that has an employee database, for example, can have a column called employee number, and each row in that column is an employee's number.
Indexes are optional structures associated with tables. Indexes can be created to increase the performance of data retrieval. Just as the index in this manual helps you quickly locate specific information, an Oracle index provides an access path to table data.
When processing a request, Oracle can use some or all of the available indexes to locate the requested rows efficiently. Indexes are useful when applications frequently query a table for a range of rows (for example, all employees with a salary greater than 1000 dollars) or a specific row.
Indexes are created on one or more columns of a table. After it is created, an index is automatically maintained and used by Oracle. Changes to table data (such as adding new rows, updating rows, or deleting rows) are automatically incorporated into all relevant indexes with complete transparency to the users.
Views are customized presentations of data in one or more tables or other views. A view can also be considered a stored query. Views do not actually contain data. Rather, they derive their data from the tables on which they are based, referred to as the base tables of the views.
Like tables, views can be queried, updated, inserted into, and deleted from, with some restrictions. All operations performed on a view actually affect the base tables of the view.
Views provide an additional level of table security by restricting access to a predetermined set of rows and columns of a table. They also hide data complexity and store complex queries.
Clusters are groups of one or more tables physically stored together because they share common columns and are often used together. Because related rows are physically stored together, disk access time improves.
Like indexes, clusters do not affect application design. Whether a table is part of a cluster is transparent to users and to applications. Data stored in a clustered table is accessed by SQL in the same way as data stored in a nonclustered table.
A synonym is an alias for any table, view, materialized view, sequence, procedure, function, package, type, Java class schema object, user-defined object type, or another synonym. Because a synonym is simply an alias, it requires no storage other than its definition in the data dictionary.
Overview of the Oracle Data Dictionary
Each Oracle database has a data dictionary. An Oracle data dictionary is a set of tables and views that are used as a read-only reference about the database. For example, a data dictionary stores information about both the logical and physical structure of the database. A data dictionary also stores the following information:
The valid users of an Oracle database
Information about integrity constraints defined for tables in the database
The amount of space allocated for a schema object and how much of it is in use
A data dictionary is created when a database is created. To accurately reflect the status of the database at all times, the data dictionary is automatically updated by Oracle in response to specific actions, such as when the structure of the database is altered. The database relies on the data dictionary to record, verify, and conduct ongoing work. For example, during database operation, Oracle reads the data dictionary to verify that schema objects exist and that users have proper access to them.
Overview of the Oracle Instance
An Oracle database server consists of an Oracle database and an Oracle instance. Every time a database is started, a system global area (SGA) is allocated and Oracle background processes are started. The combination of the background processes and memory buffers is called an Oracle instance.
Real Application Clusters: Multiple Instance Systems
Some hardware architectures (for example, shared disk systems) enable multiple computers to share access to data, software, or peripheral devices. Real Application Clusters (RAC) takes advantage of such architecture by running multiple instances that share a single physical database. In most applications, RAC enables access to a single database by users on multiple computers with increased performance.
An Oracle database server uses memory structures and processes to manage and access the database. All memory structures exist in the main memory of the computers that constitute the database system. Processes are jobs that work in the memory of these computers.
Instance Memory Structures
Oracle creates and uses memory structures to complete several jobs. For example, memory stores program code being run and data shared among users. Two basic memory structures are associated with Oracle: the system global area and the program global area. The following subsections explain each in detail.
System Global Area
The System Global Area (SGA) is a shared memory region that contains data and control information for one Oracle instance. Oracle allocates the SGA when an instance starts and deallocates it when the instance shuts down. Each instance has its own SGA.
Users currently connected to an Oracle database share the data in the SGA. For optimal performance, the entire SGA should be as large as possible (while still fitting in real memory) to store as much data in memory as possible and to minimize disk I/O.
The information stored in the SGA is divided into several types of memory structures, including the s, , and the .
Database Buffer Cache of the SGA
Database buffers store the most recently used blocks of data. The set of database buffers in an instance is the database . The buffer cache contains modified as well as unmodified blocks. Because the most recently (and often, the most frequently) used data is kept in memory, less disk I/O is necessary, and performance is improved.
Redo Log Buffer of the SGA
The redo log buffer stores redo entries&a&log of changes made to the database. The redo entries stored in the redo log buffers are written to an , which is used if database recovery is necessary. The size of the redo log is static.
Shared Pool of the SGA
The shared pool contains shared memory constructs, such as shared SQL areas. A shared SQL area is required to process every unique SQL statement submitted to a database. A shared SQL area contains information such as the parse tree and execution plan for the corresponding statement. A single shared SQL area is used by multiple applications that issue the same statement, leaving more shared memory for other uses.
Statement Handles or Cursors
A cursor is a handle or name for a private SQL area in which a parsed statement and other information for processing the statement are kept. (Oracle Call Interface, OCI, refers to these as statement handles.) Although most Oracle users rely on automatic cursor handling of Oracle utilities, the programmatic interfaces offer application designers more control over cursors.
For example, in precompiler application development, a cursor is a named resource available to a program and can be used specifically to parse SQL statements embedded within the application. Application developers can code an application so it controls the phases of SQL statement execution and thus improves application performance.
Program Global Area
The Program Global Area (PGA) is a memory buffer that contains data and control information for a server process. A PGA is created by Oracle when a server process is started. The information in a PGA depends on the Oracle configuration.
Oracle Background Processes
An Oracle database uses memory structures and processes to manage and access the database. All memory structures exist in the main memory of the computers that constitute the database system. Processes are jobs that work in the memory of these computers.
The architectural features discussed in this section enable the Oracle database to support:
Many users concurrently accessing a single database
The high performance required by concurrent multiuser, multiapplication database systems
Oracle creates a set of background processes for each instance. The background processes consolidate functions that would otherwise be handled by multiple Oracle programs running for each user process. They asynchronously perform I/O and monitor other Oracle process to provide increased parallelism for better performance and reliability.
There are numerous background processes, and each Oracle instance can use several background processes.
Process Architecture
A process is a "thread of control" or a mechanism in an operating system that can run a series of steps. Some operating systems use the terms job or task. A process generally has its own private memory area in which it runs.
An Oracle database server has two general types of processes: user processes and Oracle processes.
User (Client) Processes
User processes are created and maintained to run the software code of an application program (such as an OCI or OCCI program) or an Oracle tool (such as ). User processes also manage communication with the server process through the program interface, which is described in a later section.
Oracle Processes
Oracle processes are invoked by other processes to perform functions on behalf of the invoking process.
Oracle creates server processes to handle requests from connected user processes. A server process communicates with the user process and interacts with Oracle to carry out requests from the associated user process. For example, if a user queries some data not already in the s of the SGA, then the associated server process reads the proper s from the datafiles into the SGA.
Oracle can be configured to vary the number of user processes for each server process. In a dedicated server configuration, a server process handles requests for a single user process. A shared server configuration lets many user processes share a small number of server processes, minimizing the number of server processes and maximizing the use of available system resources.
On some systems, the user and server processes are separate, while on others they are combined into a single process. If a system uses the shared server or if the user and server processes run on different computers, then the user and server processes must be separate. Client/server systems separate the user and server processes and run them on different computers.
Overview of Accessing the Database
This section describes Oracle Net Services, as well as how to start up the database.
Network Connections
Oracle Net Services is Oracle's mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases.
Communication protocols define the way that data is transmitted and received on a network. Oracle Net Services supports communications on all major network protocols, including TCP/IP, HTTP, FTP, and WebDAV.
Using Oracle Net Services, application developers do not need to be concerned with supporting network communications in a database application. If a new protocol is used, then the database administrator makes some minor changes, while the application requires no modifications and continues to function.
Oracle Net, a component of Oracle Net Services, enables a network session from a client application to an Oracle database server. Once a network session is established, Oracle Net acts as the data courier for both the client application and the database server. It establishes and maintains the connection between the client application and database server, as well as exchanges messages between them. Oracle Net can perform these jobs because it is located on each computer in the network.
Starting Up the Database
The three steps to starting an Oracle database and making it available for systemwide use are:
Start an instance.
Mount the database.
Open the database.
A database administrator can perform these steps using the SQL*Plus STARTUP statement or Enterprise Manager. When Oracle starts an instance, it reads the server parameter file (SPFILE) or initialization parameter file to determine the values of initialization parameters. Then, it allocates an SGA and creates background processes.
How Oracle Works
The following example describes the most basic level of operations that Oracle performs. This illustrates an Oracle configuration where the user and associated server process are on separate computers (connected through a network).
has started on the computer running Oracle (often called the host or database server).
A computer running an application (a local computer or client workstation) runs the application in a . The client application attempts to establish a
to the server using the proper Oracle Net Services driver.
The server is running the proper Oracle Net Services driver. The server detects the connection request from the application and creates a dedicated server process on behalf of the user process.
The user runs a SQL statement and commits the transaction. For example, the user changes a name in a row of a table.
The server process receives the statement and checks the
for any shared SQL area that contains a similar SQL statement. If a shared SQL area is found, then the server process checks the user's access privileges to the requested data, and the previously existing shared SQL area is used to process the statement. If not, then a new shared SQL area is allocated for the statement, so it can be parsed and processed.
The server process retrieves any necessary data values from the actual datafile (table) or those stored in the SGA.
The server process modifies data in the system global area. The DBWn process writes modified blocks permanently to disk when doing so is efficient. Because the transaction is committed, the LGWR process immediately records the transaction in the redo log file.
If the transaction is successful, then the server process sends a message across the network to the application. If it is not successful, then an error message is transmitted.
Throughout this entire procedure, the other background processes run, watching for conditions that require intervention. In addition, the database server manages other users' transactions and prevents contention between transactions that request the same data.
Overview of Oracle Utilities
Oracle provides several utilities for data transfer, data maintenance, and database administration, including Data Pump Export and Import, SQL*Loader, and LogMiner.
Oracle Database Features
This section contains the following topics:
Overview of Scalability and Performance Features
Oracle includes several software mechanisms to fulfill the following important requirements of an information management system:
of a multiuser system must be maximized.
Data must be read and modified in a consistent fashion. The data a user is viewing or changing is not changed (by other users) until the user is finished with the data.
High performance is required for maximum productivity from the many users of the database system.
This contains the following sections:
Concurrency
A primary concern of a multiuser database management system is how to control concurrency, which is the simultaneous access of the same data by many users. Without adequate concurrency controls, data could be updated or changed improperly, compromising data integrity.
One way to manage data concurrency is to make each user wait for a turn. The goal of a database management system is to reduce that wait so it is either nonexistent or negligible to each user. All data manipulation language statements should proceed with as little interference as possible, and destructive interactions between concurrent transactions must be prevented. Destructive interaction is any interaction that incorrectly updates data or incorrectly alters underlying data structures. Neither performance nor data integrity can be sacrificed.
Oracle resolves such issues by using various types of locks and a multiversion consistency model. These features are based on the concept of a transaction. It is the application designer's responsibility to ensure that transactions fully exploit these concurrency and consistency features.
Read Consistency
Read consistency, as supported by Oracle, does the following:
Guarantees that the set of data seen by a statement is consistent with respect to a single point in time and does not change during statement execution (statement-level read consistency)
Ensures that readers of database data do not wait for writers or other readers of the same data
Ensures that writers of database data do not wait for readers of the same data
Ensures that writers only wait for other writers if they attempt to update identical rows in concurrent transactions
The simplest way to think of Oracle's implementation of read consistency is to imagine each user operating a private copy of the database, hence the multiversion consistency model.
Read Consistency, Undo Records, and Transactions
To manage the multiversion consistency model, Oracle must create a read-consistent set of data when a table is queried (read) and simultaneously updated (written). When an update occurs, the original data values changed by the update are recorded in the database undo records. As long as this update remains part of an uncommitted transaction, any user that later queries the modified data views the original data values. Oracle uses current information in the system global area and information in the undo records to construct a read-consistent view of a table's data for a query.
Only when a transaction is committed are the changes of the transaction made permanent. Statements that start after the user's transaction is committed only see the changes made by the committed transaction.
The transaction is key to Oracle's strategy for providing read consistency. This unit of committed (or uncommitted) SQL statements:
Dictates the start point for read-consistent views generated on behalf of readers
Controls when modified data can be seen by other transactions of the database for reading or updating
Read-Only Transactions
By default, Oracle guarantees statement-level read consistency. The set of data returned by a single query is consistent with respect to a single point in time. However, in some situations, you might also require transaction-level read consistency. This is the ability to run multiple queries within a single transaction, all of which are read-consistent with respect to the same point in time, so that queries in this transaction do not see the effects of intervening committed transactions. If you want to run a number of queries against multiple tables and if you are not doing any updating, you prefer a read-only transaction.
Locking Mechanisms
Oracle also uses locks to control concurrent access to data. When updating information, the data server holds that information with a lock until the update is submitted or committed. Until that happens, no one else can make changes to the locked information. This ensures the data integrity of the system.
Oracle provides unique non-escalating row-level locking. Unlike other data servers that &Oescalate&O locks to cover entire groups of rows or even the entire table, Oracle always locks only the row of information being updated. Because Oracle includes the locking information with the actual rows themselves, Oracle can lock an unlimited number of rows so users can work concurrently without unnecessary delays.
Automatic Locking
Oracle locking is performed automatically and requires no user action. Implicit locking occurs for SQL statements as necessary, depending on the action requested. Oracle's lock manager automatically locks table data at the row level. By locking table data at the row level, contention for the same data is minimized.
Oracle's lock manager maintains several different types of row locks, depending on what type of operation established the lock. The two general types of locks are exclusive locks and share locks. Only one exclusive lock can be placed on a resource (such as a row or a table); however, many share locks can be placed on a single resource. Both exclusive and share locks always allow queries on the locked resource but prohibit other activity on the resource (such as updates and deletes).
Manual Locking
Under some circumstances, a user might want to override default locking. Oracle allows manual override of automatic locking features at both the row level (by first querying for the rows that will be updated in a subsequent statement) and the table level.
Quiesce Database
Database administrators occasionally need isolation from concurrent non-database administrator actions, that is, isolation from concurrent non-database administrator transactions, queries, or PL/SQL statements. One way to provide such isolation is to shut down the database and reopen it in restricted mode. You could also put the system into quiesced state without disrupting users. In quiesced state, the database administrator can safely perform certain actions whose executions require isolation from concurrent non-DBA users.
Real Application Clusters
Real Application Clusters (RAC) comprises several Oracle instances running on multiple clustered computers, which communicate with each other by means of a so-called interconnect. RAC uses
software to access a shared database that resides on shared disk. RAC combines the processing power of these multiple interconnected computers to provide system redundancy, near linear scalability, and high availability. RAC also offers significant advantages for both OLTP and data warehouse systems and all systems and applications can efficiently exploit clustered environments.
You can scale applications in RAC environments to meet increasing data processing demands without changing the application code. As you add resources such as nodes or storage, RAC extends the processing powers of these resources beyond the limits of the individual components.
Portability
Oracle provides unique portability across all major platforms and ensures that your applications run without modification after changing platforms. This is because the Oracle code base is identical across platforms, so you have identical feature functionality across all platforms, for complete application transparency. Because of this portability, you can easily upgrade to a more powerful server as your requirements change.
Overview of Manageability Features
People who administer the operation of an Oracle database system, known as database administrators (DBAs), are responsible for creating Oracle databases, ensuring their smooth operation, and monitoring their use. In addition to the many alerts and advisors Oracle provides, Oracle also offers the following features:
Self-Managing Database
Oracle Database provides a high degree of self-management - automating routine DBA tasks and reducing complexity of space, memory, and resource administration. Oracle self-managing database features include the following: automatic undo management, dynamic memory management, Oracle-managed files, mean time to recover, free space management, multiple block sizes, and Recovery Manager (RMAN).
Oracle Enterprise Manager
Enterprise Manager is a system management tool that provides an integrated solution for centrally managing your heterogeneous environment. Combining a graphical console, Oracle Management Servers, Oracle Intelligent Agents, common services, and administrative tools, Enterprise Manager provides a comprehensive systems management platform for managing Oracle products.
From the client interface, the Enterprise Manager Console, you can perform the following tasks:
Administer the complete Oracle environment, including databases, iAS servers, applications, and services
Diagnose, modify, and tune multiple databases
Schedule tasks on multiple systems at varying time intervals
Monitor database conditions throughout the network
Administer multiple network nodes and services from many locations
Share tasks with other administrators
Group related targets together to facilitate administration tasks
Launch integrated Oracle and third-party tools
Customize the display of an Enterprise Manager administrator
SQL*Plus is a tool for entering and running ad-hoc database statements. It lets you run SQL statements and PL/SQL blocks, and perform many additional tasks as well.
Automatic Storage Management
Automatic Storage Management automates and simplifies the layout of datafiles, control files, and log files. Database files are automatically distributed across all available disks, and database storage is rebalanced whenever the storage configuration changes. It provides redundancy through the mirroring of database files, and it improves performance by automatically distributing database files across all available disks. Rebalancing of the database's storage automatically occurs whenever the storage configuration changes.
The Scheduler
To help simplify management tasks, as well as providing a rich set of functionality for complex scheduling needs, Oracle provides a collection of functions and procedures in the DBMS_SCHEDULER package. Collectively, these functions are called the Scheduler, and they are callable from any PL/SQL program.
The Scheduler lets database administrators and application developers control when and where various tasks take place in the database environment. For example, database administrators can schedule and monitor database maintenance jobs such as backups or nightly data warehousing loads and extracts.
Database Resource Manager
Traditionally, the operating systems regulated resource management among the various applications running on a system, including Oracle databases. The Database Resource Manager controls the distribution of resources among various sessions by controlling the execution schedule inside the database. By controlling which sessions run and for how long, the Database Resource Manager can ensure that resource distribution matches the plan directive and hence, the business objectives.
Overview of Database Backup and Recovery Features
In every database system, the possibility of a system or hardware failure always exists. If a failure occurs and affects the database, then the database must be recovered. The goals after a failure are to ensure that the effects of all committed transactions are reflected in the recovered database and to return to normal operation as quickly as possible while insulating users from problems caused by the failure.
Oracle provides various mechanisms for the following:
Database recovery required by different types of failures
Flexible recovery operations to suit any situation
Availability of data during backup and recovery operations so users of the system can continue to work
Types of Failures
Several circumstances can halt the operation of an Oracle database. The most common types of failure are described in the following table.
Oracle provides for complete media recovery from all possible types of hardware failures, including disk failures. Options are provided so that a database can be completely recovered or partially recovered to a specific point in time.
If some datafiles are damaged in a disk failure but most of the database is intact and operational, the database can remain open while the required tablespaces are individually recovered. Therefore, undamaged portions of a database are available for normal use while damaged portions are being recovered.
Structures Used for Recovery
Oracle uses several structures to provide complete recovery from an instance or disk failure: the redo log, undo records, a control file, and database backups.
The Redo Log
The redo log is a set of files that protect altered database data in memory that has not been written to the datafiles. The redo log can consist of the online redo log and the archived redo log.
The online redo log is a set of two or more online redo log files that record all changes made to the database, including uncommitted and committed changes. Redo entries are temporarily stored in redo log buffers of the system global area, and the background process LGWR writes the redo entries sequentially to an online redo log file. LGWR writes redo entries continually, and it also writes a commit record every time a user process commits a transaction.
Optionally, filled online redo files can be manually or automatically archived before being reused, creating archived redo logs. To enable or disable archiving, set the database in one of the following modes:
ARCHIVELOG: The filled online redo log files are archived before they are reused in the cycle.
NOARCHIVELOG: The filled online redo log files are not archived.
In ARCHIVELOG mode, the database can be completely recovered from both instance and disk failure. The database can also be backed up while it is open and available for use. However, additional administrative operations are required to maintain the archived redo log.
If the database redo log operates in NOARCHIVELOG mode, then the database can be completely recovered from instance failure, but not from disk failure. Also, the database can be backed up only while it is completely closed. Because no archived redo log is created, no extra work is required by the database administrator.
Undo Records
Undo records are stored in undo tablespaces. Oracle uses the undo data for a variety of purposes, including accessing before-images of blocks changed in uncommitted transactions. During database recovery, Oracle applies all changes recorded in the redo log and then uses undo information to roll back any uncommitted transactions.
Control Files
The control files include information about the file structure of the database and the current log sequence number being written by LGWR. During normal recovery procedures, the information in a control file guides the automatic progression of the recovery operation.
Database Backups
Because one or more files can be physically damaged as the result of a disk failure, media recovery requires the restoration of the damaged files from the most recent operating system backup of a database. You can either back up the database files with Recovery Manager (RMAN), or use operating system utilities. RMAN is an Oracle utility that manages backup and recovery operations, creates backups of database files (datafiles, control files, and archived redo log files), and restores or recovers a database from backups.
Overview of High Availability Features
Computing environments configured to provide nearly full-time availability are known as high availability systems. Such systems typically have redundant hardware and software that makes the system available despite failures. Well-designed high availability systems avoid having single points-of-failure.
When failures occur, the fail over process moves processing performed by the failed component to the backup component. This process remasters systemwide resources, recovers partial or failed transactions, and restores the system to normal, preferably within a matter of microseconds. The more transparent that fail over is to users, the higher the availability of the system.
Oracle has a number of products and features that provide high availability in cases of unplanned downtime or planned downtime. These include Fast-Start Fault Recovery, Real Application Clusters, , backup and recovery solutions, Oracle Flashback, partitioning, Oracle Data Guard, LogMiner, multiplexed redo log files, online reorganization. These can be used in various combinations to meet specific high availability needs.
Overview of Business Intelligence Features
This section describes several business intelligence features.
Data Warehousing
A data warehouse is a relational database designed for query and analysis rather than for transaction processing. It usually contains historical data derived from transaction data, but it can include data from other sources. It separates analysis workload from transaction workload and enables an organization to consolidate data from several sources.
In addition to a relational database, a data warehouse environment includes an extraction, transportation, transformation, and loading (ETL) solution, an online analytical processing (OLAP) engine, client analysis tools, and other applications that manage the process of gathering data and delivering it to business users.
Extraction, Transformation, and Loading (ETL)
You must load your data warehouse regularly so that it can serve its purpose of facilitating business analysis. To do this, data from one or more operational systems must be extracted and copied into the warehouse. The process of extracting data from source systems and bringing it into the data warehouse is commonly called ETL, which stands for extraction, transformation, and loading.
Materialized Views
A materialized view provides access to table data by storing the results of a query in a separate schema object. Unlike an ordinary view, which does not take up any storage space or contain any data, a materialized view contains the rows resulting from a query against one or more base tables or views. A materialized view can be stored in the same database as its base tables or in a different database.
Materialized views stored in the same database as their base tables can improve query performance through query rewrites. Query rewrite is a mechanism where Oracle or applications from the end user or database transparently improve query response time, by automatically rewriting the SQL query to use the materialized view instead of accessing the original tables. Query rewrites are particularly useful in a data warehouse environment.
Bitmap Indexes in Data Warehousing
Data warehousing environments typically have large amounts of data and ad hoc queries, but a low level of concurrent database manipulation language (DML) transactions. For such applications, bitmap indexing provides:
Reduced response time for large classes of ad hoc queries
Reduced storage requirements compared to other indexing techniques
Dramatic performance gains even on hardware with a relatively small number of CPUs or a small amount of memory
Efficient maintenance during parallel DML and loads
Fully indexing a large table with a traditional B-tree index can be prohibitively expensive in terms of space because the indexes can be several times larger than the data in the table. Bitmap indexes are typically only a fraction of the size of the indexed data in the table.
Table Compression
To reduce disk use and memory use (specifically, the buffer cache), you can store tables and partitioned tables in a co