PARALLEL PROCESS:
DEFINITION - In computers, parallel processing is the processing of program instructions by dividing them among multiple processors with the objective of running a program in less time. In the earliest computers, only one program ran at a time. A computation-intensive program that took one hour to run and a tape copying program that took one hour to run would take a total of two hours to run. An early form of parallel processing allowed the interleaved execution of both programs together. The computer would start an I/O operation, and while it was waiting for the operation to complete, it would execute the processor-intensive program. The total execution time for the two jobs would be a little over one hour.
The Oracle Parallel Query Option
Introduced in later versions of Oracle7 the parallel query option (PQO) allows multiple processes to simultaneously fetch records and perform sorting operations. This parallelization of operations can lead to impressive speed improvements in a properly set up parallel environment.
The most important item to specify in a parallel environment is the number of parallel query slaves. Too few and you don’t get the full benefits, too many and they end up competing with each other for resources. Of course parallel operations are of little or no benefit if your system doesn’t have parallel processors and your tables aren’t spread across multiple disks in a stripe set or partitioned. Along with the number of parallel query slaves the degree of parallel (DOP) for the tables and indexes needs to be set properly.
The maximum number of parallel query slaves should generally be set to at least twice the number of CPUs or to twice the number of disks that he object was spread across. The DOP can be determined by forcing a full table scan for tables (use a where 1=2 in a select count(*) from the table) and then timing the response for different DOP settings. These numbers are then adjusted up or down depending on performance.
Parallel query settings
There are several initialization parameters that pertain to parallel query:
parallel_adaptive_multi_user
TRUE or FALSE, defaults to FALSE, when set to TRUE, enables an adaptive algorithm designed to improve performance in multi-user environments that use Parallel Query(PQ). It does this by automatically reducing the requested degree of parallelism based on the current number of active PQ users on the system. The effective degree of parallelism will be based on the degree of parallelism from the table or hint divided by the total number of PQ users. The algorithm assumes that the degree of parallelism provided has been tuned for optimal performance in a single user environment.
At Oracle Openworld 2007, Oracle recommends never to turn-on the parallel_adaptive_multi_user parameter.
optimizer_percent_parallel
Specifies the amount of parallelism that the optimizer uses in its cost functions. The default of 0 means that the optimizer chooses the best serial plan. A value of 100 means that the optimizer uses each object's degree of parallelism in computing the cost of a full table scan operation. Low values favor indexes, and high values favor table scans.
Cost-based optimization will always be used for any query that references an object with a nonzero degree of parallelism. For such queries a RULE hint or optimizer mode or goal will be ignored. Use of a FIRST_ROWS hint or optimizer mode will override a nonzero setting of OPTIMIZER_PERCENT_PARALLEL.
parallel_min_percent
This specifies the minimum percent of threads required for parallel query. Setting this parameter ensures that a parallel query will not be executed sequentially if adequate resources are not available. The default value of 0 means that this parameter is not used.
If too few query slaves are available, an error message is displayed and the query is not executed. Consider the following settings:
PARALLEL_MIN_PERCENT = 50
PARALLEL_MIN_SERVERS = 5
PARALLEL_MAX_SERVERS = 10
In a system with 20 instances up and running, the system would have a maximum of 200 query slaves available. If 190 slaves are already in use and a new user wants to run a query with 40 slaves (for example, degree 2 instances 20), an error message would be returned because 20 instances (that is, 50% of 40) are not available.
parallel_min_servers
This specifies the minimum number of query server processes for an instance. This is also the number of query server processes Oracle creates when the instance is started.
parallel_max_servers
Parallel_max_servers specifies the maximum number of parallel query servers or parallel recovery processes for an instance. Oracle will increase the number of query servers as demand requires from the number created at instance startup up to this value. The same value should be used for all instances in a parallel server environment.
Proper setting of the PARALLEL_MAX_SERVERS parameter ensures that the number of query servers in use will not cause a memory resource shortage during periods of peak database use.
If PARALLEL_MAX_SERVERS is set too low, some queries may not have a query server available to them during query processing.
Setting PARALLEL_MAX_SERVERS too high leads to memory resource shortages during peak periods, which can degrade performance. For each instance to which you do not want to apply the parallel query option, set this initialization parameter to zero.
If you have reached the limit of PARALLEL_MAX_SERVERS on an instance and you attempt to query a GV$ view, one additional parallel server process will be spawned for this purpose. This extra process will serve any subsequent GV$ queries until expiration of the PARALLEL_SERVER_IDLE_TIME, at which point the process will terminate. The extra process is not available for any parallel operation other than GV$ queries.
Note that if PARALLEL_MAX_SERVERS is set to zero for an instance, then no additional parallel server process will be allocated to accommodate a GV$ query.
parallel_server_idle_time
Specifies the amount of idle time after which Oracle terminates a process for parallel operations (parallel query, parallel DML, or parallel DDL). This value is expressed in minutes. The parameter must be set to 1 or greater for the query processes to terminate. 0 means the processes are never terminated.
parallel_execution_message_size
Specifies the size of messages for parallel execution (Parallel Query, PDML, Parallel Recovery, replication). The default value should be adequate for most applications. Typical values are 2148 or 4096 bytes. Larger values would require a larger shared pool.
parallel_min_message_pool
The parallel_min_message_pool parameter defaults to (cpus*parallel_max_servers*1.5*(OS message buffer size) or cpus*5*1.5*(OS message size)). Specifies the minimum permanent amount of memory which will be allocated from the SHARED POOL, to be used for messages in parallel execution.
This memory is allocated at startup time if PARALLEL_MIN_SERVERS is set to a non-zero value, or when the server is first allocated. Setting this parameter is most effective when PARALLEL_MIN_SERVERS is set to a non-zero value, because the memory will be allocated in a contiguous section.
This parameter should only be set if the default formula is known to be significantly inaccurate. setting this parameter too high will lead to a shortage of memory for the shared pool; setting it too low will lead to costlier memory allocation when doing parallel execution. This parameter cannot be set to a number higher than 90% of the shared pool.
parallel_broadcast_enabled
This defaults to FALSE and allows you to improve performance in certain cases involving hash and merge joins. When set to TRUE, if you are joining a very large join result set with a very small result set (size being measured in bytes, rather than number of rows), the optimizer has the option of broadcasting the row sources of the small result set, such that a single table queue will send all of the small set's rows to each of the parallel servers which are processing the rows of the larger set. The result is enhanced performance.
shared_pool_size
The shared pool will have to be increased in size to accommodate the parallel query message areas and IO queues. I suggest that the LARGE POOL be designated to prevent PQO from causing shared pool problems.
large_pool_size
The large pool will automatically be configured at a minimum size of 600k if certain initialization parameters are set in Oracle8. I suggest manually setting the size.
Oracle Parallel Automatic tuning parameter:
Oracle parallel query (OPQ) is a great way to speed full full-scan operations, but Oracle parallelism can be problematic if it is not implemented properly.
Oracle provides a general method for implementing parallelism with the parallel_automatic_tuning=true parameter setting, but there are cases when using PAT can actually degrade your Oracle performance. The Oracle docs note:
"With parallel automatic tuning enabled, Oracle determines parameter settings for each environment based on the number of CPUs on your system and the value set for PARALLEL_THREADS_PER_CPU.
The default values Oracle sets for parallel execution processing when PARALLEL_AUTOMATIC_TUNING is TRUE are usually optimal for most environments. In most cases, Oracle's automatically derived settings are at least as effective as manually derived settings."
I disagree.
The parallel_automatic_tuning parameter feature was created for DSS and Data Warehouse environments using the all_rows optimizer mode on servers with many CPU processors to ensure that the common full table scans are parallelized to an optimal DEGREE.
However, parallel_automatic_tuning is not always appropriate for OLTP and online systems, where setting parallel_automatic_tuning may change the SQL optimizers perception of the costs of full scan operations, causing indexes not to be used.
For non-warehouse environments, I do not recommend setting parallel_automatic_tuning, or turning on parallel query at the system or table level. I get the best performance my manually adding the "parallel" hint to query where I want the full can to be done in parallel.
PARALLEL_THREADS_PER_CPU specifies the default degree of parallelism for the instance and determines the parallel adaptive and load balancing algorithms. The parameter describes the number of parallel execution processes or threads that a CPU can handle during parallel execution.
The default is platform-dependent and is adequate in most cases. You should decrease the value of this parameter if the machine appears to be overloaded when a representative parallel query is executed. You should increase the value if the system is I/O bound.
* Parallel query. The ability to break up the execution of a SELECT statement into multiple tasks, and then to execute those tasks in parallel using multiple processors.
* Parallel data loading. The ability to run multiple SQL*Loader sessions in parallel, which all load data into the same table.
* Parallel DML (Data Manipulation Language). The ability to parallelize INSERT, UPDATE, and DELETE statements.
* Parallel DDL (object creation). The ability to parallelize DDL statements such as CREATE TABLE, CREATE INDEX, and ALTER INDEX.
* Parallel recovery. The ability to use multiple processes to perform instance and media recovery.
* Parallel replication propagation. The ability to propagate changes from one database to another using multiple processes working together in parallel.
Wednesday, December 23, 2009
Tuesday, December 22, 2009
ORACLE HISTORY (CORPORATE,TECHNICAL,VERSION,EDITIONS,PLATFORMS,FEATURES,TOOLS,SUPPORT,CERTIFICATION etc)
Corporate/technical timeline
* 1977: Larry Ellison and friends founded Software Development Laboratories.
* 1979: SDL changed its company-name to "Relational Software, Inc." (RSI) and introduced its product Oracle V2 as an early commercially-available relational database system. The version did not support transactions, but implemented the basic SQL functionality of queries and joins. (RSI never released a version 1 - instead calling the first version version 2 as a marketing gimmick.)
* 1982: RSI in its turn changed its name, becoming known as "Oracle Corporation",to align itself more closely with its flagship product.
* 1983: The company released Oracle version 3, which it had re-written using the C programming language and which supported COMMIT and ROLLBACK functionality for transactions. Version 3 extended platform support from the existing Digital VAX/VMS systems to include Unix environments.
* 1984: Oracle Corporation released Oracle version 4, which supported read-consistency.
* 1985: Oracle Corporation released Oracle version 5, which supported the client-server model—a sign of networks becoming more widely available in the mid-1980s.
* 1986: Oracle version 5.1 started supporting distributed queries.
* 1988: Oracle RDBMS version 6 came out with support for PL/SQL embedded within Oracle Forms v3 (version 6 could not store PL/SQL in the database proper), row-level locking and hot backups.
* 1989: Oracle Corporation entered the application products market and developed its ERP product, (later to become part of the Oracle E-Business Suite), based on the Oracle relational database.
* 1990: the release of Oracle Applications release 8
* 1992: Oracle version 7 appeared with support for referential integrity, stored procedures and triggers.
* 1997: Oracle Corporation released version 8, which supported object-oriented development and multimedia applications.
* 1999: The release of Oracle8i aimed to provide a database inter-operating better with the Internet (the i in the name stands for "Internet"). The Oracle 8i database incorporated a native Java virtual machine (Oracle JVM).
* 2000: Oracle E-Business Suite 11i pioneers integrated enterprise application software
* 2001: Oracle9i went into release with 400 new features, including the ability to read and write XML documents. 9i also provided an option for Oracle RAC, or "Real Application Clusters", a computer-cluster database, as a replacement for the Oracle Parallel Server (OPS) option.
* 2003: Oracle Corporation released Oracle Database 10g. (The g stands for "grid"; emphasizing a marketing thrust of presenting 10g as "grid-computing ready".)
* 2005: Oracle Database 10.2.0.1—also known as Oracle Database 10g Release 2 (10gR2)—appeared.
* 2006: Oracle Corporation announces Unbreakable Linux
* 2007: Oracle Database 10g release 2 sets a new world record TPC-H 3000 GB benchmark result
* 2007: Oracle Corporation released Oracle Database 11g for Linux and for Microsoft Windows.
* 2008: Oracle Corporation acquires BEA Systems.
* 2009: Oracle Corporation acquires Sun Microsystems. Note: as of November 2009 the acquisition awaits approval from the European Commission.
Version numbering
Oracle products have historically followed their own release-numbering and naming conventions. With the Oracle RDBMS 10g release, Oracle Corporation started standardizing all current versions of its major products using the "10g" label, although some sources continued to refer to Oracle Applications Release 11i as Oracle 11i. Major database-related products and some of their versions include:
* Oracle Application Server 10g (also known as "Oracle AS 10g"): a middleware product;
* Oracle Applications Release 11i (aka Oracle e-Business Suite, Oracle Financials or Oracle 11i): a suite of business applications;
* Oracle Developer Suite 10g (9.0.4);
* Oracle JDeveloper 10g: a Java integrated development environment;
Since version 5, Oracle's RDBMS release numbering has used the following codes:
* Oracle5
* Oracle6
* Oracle7: 7.0.16—7.3.4
* Oracle8 Database: 8.0.3—8.0.6
* Oracle8i Database Release 1: 8.1.5.0—8.1.5.1
* Oracle8i Database Release 2: 8.1.6.0—8.1.6.3
* Oracle8i Database Release 3: 8.1.7.0—8.1.7.4
* Oracle9i Database Release 1: 9.0.1.0—9.0.1.5 (patchset as of December 2003)
* Oracle9i Database Release 2: 9.2.0.1—9.2.0.8 (patchset as of April 2007)
* Oracle Database 10g Release 1: 10.1.0.2—10.1.0.5 (patchset as of February 2006)
* Oracle Database 10g Release 2: 10.2.0.1—10.2.0.4 (patchset as of April 2008)
* Oracle Database 11g Release 1: 11.1.0.6—11.1.0.7 (patchset as of September 2008)
* Oracle Database 11g Release 2: 11.2.0.1 (released 2009-09-01)
The version-numbering syntax within each release follows the pattern: major.maintenance.application-server.component-specific.platform-specific.
For example, "10.2.0.1 for 64-bit Solaris" means: 10th major version of Oracle, maintenance level 2, Oracle Application Server (OracleAS) 0, level 1 for Solaris 64-bit.
List of claimed firsts
Oracle Corporation claims to have provided:
* the first commercially-available SQL-based database (1979)
* the first database to support symmetric multiprocessing (SMP) (1983)
* the first distributed database (1986)
* the first database product tested to comply with the ANSI SQL standard (1993)
* the first 64-bit database (1995)
* the first database to incorporate a native JRE (1998)
* the first proprietary RDBMS to become available on Linux (1998)
* the first database to support XML (1999)
Editions
Over and above the different versions of the Oracle database management software, Oracle Corporation subdivides its product into varying "editions" - apparently for marketing and license-tracking reasons. In approximate order of decreasing scale, we find:
* Enterprise Edition (EE) includes more features than the 'Standard Edition', especially in the areas of performance and security. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running 4 or more CPUs. EE has no memory limits, and can utilize clustering using Oracle RAC software.
* Standard Edition (SE) contains base database functionality. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running from one to four CPUs. If the number of CPUs exceeds 4 CPUs, the user must convert to an Enterprise license. SE has no memory limits, and can utilize clustering with Oracle RAC at no additional charge.
* Standard Edition One, introduced with Oracle 10g, has some additional feature-restrictions. Oracle Corporation markets it for use on systems with one or two CPUs. It has no memory limitations.
* Express Edition ('Oracle Database XE'), introduced in 2005, offers Oracle 10g free to distribute on Windows and Linux platforms. It has a footprint of only 150 MB and is restricted to the use of a single CPU, a maximum of 4 GB of user data. Although it can install on a server with any amount of memory, it uses a maximum of 1 GB. Support for this version comes exclusively through on-line forums and not through Oracle support.
* Oracle Database Lite, intended for running on mobile devices. The database located on the mobile device can synchronize with a server-based installation.
Host platforms
Prior to releasing Oracle9i in 2001, Oracle Corporation ported its database product to a wide variety of platforms. More recently Oracle Corporation has consolidated on a smaller range of operating-system platforms.
As of October 2006, Oracle Corporation supported the following operating systems and hardware platforms for Oracle Database 10g:
* Apple Mac OS X Server: PowerPC
* HP HP-UX: PA-RISC, Itanium
* HP Tru64 UNIX: Alpha
* HP OpenVMS: Alpha, Itanium
* IBM AIX5L: IBM POWER
* IBM z/OS: zSeries
* Linux: x86, x86-64, PowerPC, zSeries, Itanium
* Microsoft Windows: x86, x86-64, Itanium
* Sun Solaris: SPARC, x86, x86-64
Database options
Oracle Corporation refers to some extensions to the core functionality of the Oracle database as "database options". As of 2008 such options include:
* Active Data Guard (extends Oracle Data Guard physical standby functionality in 11g)
* Advanced Security (adds data encryption methods)
* Content database (provides a centralized repository for unstructured information)
* Database Vault (enforces extra security on data access)
* Data Mining (ODM) (mines for patterns in existing data)
* In-Memory Database Cache (utilizes TimesTen technology)
* Label Security (enforces row-level security)
* Management Packs (various)
* Oracle Answers (for ad-hoc analysis and reporting)
* Oracle OLAP (adds analytical processing)
* Oracle Programmer (provides programmatic access to Oracle databases via precompilers, interfaces and bindings)
* Partitioning (granularizes tables and indexes for efficiency)
* Real Application Clusters (RAC) (coordinates multiple database servers, together accessing the same database)
* Oracle Real Application Testing (new at version 11g)—including Database Replay (for testing workloads) and SQL Performance Analyzer (SPA) (for preserving SQL efficiency in changing environments)
* Records database (a records management application)
* Oracle Spatial (integrates relational data with geographic information systems (GIS))
* Transparent Gateway for connecting to non-Oracle systems. Offers optimized solution, with more functionality and better performance than Oracle Generic Connectivity.
* Total Recall (optimizes long-term storage of historical data)
* Oracle Warehouse Builder (in various forms and sub-options)
This list is incomplete; you can help by expanding it.
In most cases, using these options entails extra licensing costs.
Suites
In addition to its RDBMS, Oracle Corporation has released several related suites of tools and applications relating to implementations of Oracle databases. For example:
* Oracle Application Server, a J2EE-based application server, aids in developing and deploying applications which utilise Internet technologies and a browser.
* Oracle Collaboration Suite contains messaging, groupware and collaboration applications.
* Oracle Developer Suite contains software development tools, including JDeveloper.
* Oracle E-Business Suite collects together applications for enterprise resource planning (including Oracle Financials), customer relationship management and human resources management (Oracle HR).
* Oracle Enterprise Manager (OEM) used by database administrators (DBAs) to manage the DBMS, and recently in version 10g, a web-based rewrite of OEM called "Oracle Enterprise Manager Database Control". Oracle Corporation has dubbed the super-Enterprise-Manager used to manage a grid of multiple DBMS and Application Servers "Oracle Enterprise Manager Grid Control".
* Oracle Programmer/2000, a bundling of interfaces for 3GL programming languages, marketed with Oracle7 and Oracle8.
Database "features"
Apart from the clearly-defined database options, Oracle databases may include many semi-autonomous software sub-systems, which Oracle Corporation sometimes refers to as "features" in a sense subtly different from the normal usage of the word. For example, Oracle Data Guard counts officially as a "feature", but the command-stack within SQL*Plus, though a usability feature, does not appear in the list of "features" in Oracle's list. Such "features" may include (for example):
* Active Session History (ASH), the collection of data for immediate monitoring of very recent database activity.
* Automatic Workload Repository (AWR), providing monitoring services to Oracle database installations from Oracle version 10. Prior to the release of Oracle version 10, the Statspack facility provided similar functionality.
* Clusterware
* Data Aggregation and Consolidation
* Data Guard for high availability
* Generic Connectivity for connecting to non-Oracle systems.
* Data Pump utilities, which aid in importing and exporting data and metadata between databases
* Database Resource Manager (DRM), which controls the use of computing resources.
* Fine-grained auditing (FGA) (in Oracle Enterprise Edition) supplements standard security-auditing features
* Flashback for selective data recovery and reconstruction
* iSQL*Plus, a web-browser-based graphical user interface (GUI) for Oracle database data-manipulation (compare SQL*Plus)
* Oracle Data Access Components (ODAC), tools which consist of:
o Oracle Data Provider for .NET (ODP.NET)
o Oracle Developer Tools (ODT) for Visual Studio
o Oracle Providers for ASP.NET
o Oracle Database Extensions for .NET
o Oracle Provider for OLE DB
o Oracle Objects for OLE
o Oracle Services for Microsoft Transaction Server
* Oracle-managed files (OMF) -- a feature allowing automated naming, creation and deletion of datafiles at the operating-system level.
* Recovery Manager (rman) for database backup, restoration and recovery
* SQL*Plus, a program that allows users to interact with Oracle database(s) via SQL and PL/SQL commands on a command-line. Compare iSQL*Plus.
This list is incomplete; you can help by expanding it.
Standalone tools
Users can develop applications in Java and PL/SQL using tools such as Oracle JDeveloper, Oracle Forms, or Oracle Reports. Oracle Corporation has started a drive toward 'wizard'-driven environments with a view to enabling non-programmers to produce simple data-driven applications.
Oracle SQL Developer, a free graphical tool for database development, allows developers to browse database objects, run SQL statements and SQL scripts, and edit and debug PL/SQL statements. It incorporates standard and customized reporting.
Other databases marketed by Oracle Corporation
By acquiring other technology in the database field, Oracle Corporation has taken over:
* TimesTen, a memory-resident database that can cache transactions and synchronize data with a centralized Oracle database server. It functions as a real-time infrastructure software product intended for the management of low-latency, high-volume data, of events and of transactions.
* BerkeleyDB, a simple, high-performance, embedded database
* Oracle Rdb, a legacy relational database for the OpenVMS operating system
* MySQL a relational database purchased as part of its immediate previous owner, Sun Microsystems
Use
The Oracle RDBMS has had a reputation among novice users as difficult to install on Linux systems. Oracle Corporation has packaged recent versions for several popular Linux distributions in an attempt to minimize installation challenges beyond the level of technical expertise required to install a database server.
Official support
Users who have Oracle support contracts can use Oracle's MetaLink web site. MetaLink provides users of Oracle Corporation products with a repository of reported problems, diagnostic scripts and solutions. It also integrates with the provision of support tools, patches and upgrades.
The Remote Diagnostic Agent or RDA can operate as a command-line diagnostic tool executing a script. The data captured provides an overview of the Oracle Database environment intended for diagnostic and trouble-shooting. Within RDA, the HCVE (Health Check Validation Engine) can verify and isolate host system environmental issues that may affect the performance of Oracle software.
Database-related guidelines
Oracle Corporation also endorses certain practices and conventions as enhancing the use of its database products. These include:
* Oracle Maximum Availability Architecture (MAA), guidelines on developing high-availability systems
* Optimal Flexible Architecture (OFA), blueprints for mapping Oracle-database objects to file-systems
Oracle Certification Program
Main article: Oracle Certification Program
The Oracle Certification Program, a professional certification program, includes the administration of Oracle Databases as one of its main certification paths. It contains three levels not upto limits.
1. Oracle Certified Associate (OCA)
2. Oracle Certified Professional (OCP)
3. Oracle Certified Master (OCM)
User groups
A variety of official (Oracle-sponsored) and unofficial Oracle User Groups has grown up of users and developers of Oracle databases. They include:
* Oracle Technology Network
* Independent Oracle Users Group
* Geographical/regional user groups
* Product-centric user groups
* Industry-centric user groups
* The Oak Table Network
* Usenet newsgroups
Market position
In the market for relational databases, Oracle Database competes against commercial products such as IBM's DB2 UDB and Microsoft SQL Server. Oracle and IBM tend to battle for the mid-range database market on UNIX and Linux platforms, while Microsoft dominates the mid-range database market on Microsoft Windows platforms. However, since they share many of the same customers, Oracle and IBM tend to support each other's products in many middleware and application categories (for example: WebSphere, PeopleSoft, and Siebel Systems CRM), and IBM's hardware divisions work closely with Oracle on performance-optimizing server-technologies (for example, Linux on zSeries). The two companies have a relationship perhaps best described as "coopetition". Niche commercial competitors include Teradata (in data warehousing and business intelligence), Software AG's ADABAS, Sybase, and IBM's Informix, among many others.
Increasingly, the Oracle database products compete against open-source relational database systems, particularly PostgreSQL, Firebird, and MySQL. Oracle acquired Innobase, supplier of the InnoDB codebase to MySQL, in part to compete better in the open source market. Database products developed on the basis of the open-source model generally cost significantly less to acquire than Oracle systems.
In 2007, competition with SAP AG occasioned litigation from Oracle Corporation.
Pricing
Oracle Corporation offers term licensing for all Oracle products. It bases the list price for a term-license on a specific percentage of the perpetual license price.
Enterprise Edition
As of March 2006, the database that costs the most per machine-processor among Oracle database editions.
Standard Edition
Cheaper: it can run on up to four processors but has fewer features than Enterprise Edition—it lacks proper parallelization,etc; but remains quite suitable for running medium-sized applications.
Standard ONE
Sells even more cheaply, but remains limited to two CPUs. Standard Edition ONE sells on a per-seat basis with a five-user minimum. Oracle Corporation usually sells the licenses with an extra 22% cost for support and upgrades (access to MetaLink—Oracle Corporation's support site) which customers need to renew annually.
Oracle Express Edition (Oracle XE)
An addition to the Oracle database product family (beta version released in 2005, production version released in February 2006), offers a free version of the Oracle RDBMS, but one limited to 4 GB of user data and to 1 GB of RAM (SGA+PGA). XE will use no more than one CPU and lacks an internal JVM. XE runs only on Windows and on Linux, not on AIX, Solaris, HP-UX and the other operating systems available for other editions.
As computers running Oracle often have eight or more processors, the software price can rise into the hundreds of thousands of dollars. The total cost of ownership often exceeds this, as large Oracle installations usually require experienced and trained database administrators to do the set-up properly. Because of the product's large installed base and available training courses, Oracle specialists in some areas have become a more abundant resource than those for more exotic databases. Oracle frequently provides special training offers for database-administrators.
On Linux, Oracle's certified configurations include mostly commercial Linux distributions (Red Hat Enterprise Linux 3 and 4, SuSE SLES8 and 9, Asianux) which can cost in a range from a few hundred to a few thousand USD per year (depending on processor architecture and the support package purchased).
The Oracle database system can also install and run on freely-available Linux distributions such as the Red Hat-based Centos,or Debian-based systems.
* 1977: Larry Ellison and friends founded Software Development Laboratories.
* 1979: SDL changed its company-name to "Relational Software, Inc." (RSI) and introduced its product Oracle V2 as an early commercially-available relational database system. The version did not support transactions, but implemented the basic SQL functionality of queries and joins. (RSI never released a version 1 - instead calling the first version version 2 as a marketing gimmick.)
* 1982: RSI in its turn changed its name, becoming known as "Oracle Corporation",to align itself more closely with its flagship product.
* 1983: The company released Oracle version 3, which it had re-written using the C programming language and which supported COMMIT and ROLLBACK functionality for transactions. Version 3 extended platform support from the existing Digital VAX/VMS systems to include Unix environments.
* 1984: Oracle Corporation released Oracle version 4, which supported read-consistency.
* 1985: Oracle Corporation released Oracle version 5, which supported the client-server model—a sign of networks becoming more widely available in the mid-1980s.
* 1986: Oracle version 5.1 started supporting distributed queries.
* 1988: Oracle RDBMS version 6 came out with support for PL/SQL embedded within Oracle Forms v3 (version 6 could not store PL/SQL in the database proper), row-level locking and hot backups.
* 1989: Oracle Corporation entered the application products market and developed its ERP product, (later to become part of the Oracle E-Business Suite), based on the Oracle relational database.
* 1990: the release of Oracle Applications release 8
* 1992: Oracle version 7 appeared with support for referential integrity, stored procedures and triggers.
* 1997: Oracle Corporation released version 8, which supported object-oriented development and multimedia applications.
* 1999: The release of Oracle8i aimed to provide a database inter-operating better with the Internet (the i in the name stands for "Internet"). The Oracle 8i database incorporated a native Java virtual machine (Oracle JVM).
* 2000: Oracle E-Business Suite 11i pioneers integrated enterprise application software
* 2001: Oracle9i went into release with 400 new features, including the ability to read and write XML documents. 9i also provided an option for Oracle RAC, or "Real Application Clusters", a computer-cluster database, as a replacement for the Oracle Parallel Server (OPS) option.
* 2003: Oracle Corporation released Oracle Database 10g. (The g stands for "grid"; emphasizing a marketing thrust of presenting 10g as "grid-computing ready".)
* 2005: Oracle Database 10.2.0.1—also known as Oracle Database 10g Release 2 (10gR2)—appeared.
* 2006: Oracle Corporation announces Unbreakable Linux
* 2007: Oracle Database 10g release 2 sets a new world record TPC-H 3000 GB benchmark result
* 2007: Oracle Corporation released Oracle Database 11g for Linux and for Microsoft Windows.
* 2008: Oracle Corporation acquires BEA Systems.
* 2009: Oracle Corporation acquires Sun Microsystems. Note: as of November 2009 the acquisition awaits approval from the European Commission.
Version numbering
Oracle products have historically followed their own release-numbering and naming conventions. With the Oracle RDBMS 10g release, Oracle Corporation started standardizing all current versions of its major products using the "10g" label, although some sources continued to refer to Oracle Applications Release 11i as Oracle 11i. Major database-related products and some of their versions include:
* Oracle Application Server 10g (also known as "Oracle AS 10g"): a middleware product;
* Oracle Applications Release 11i (aka Oracle e-Business Suite, Oracle Financials or Oracle 11i): a suite of business applications;
* Oracle Developer Suite 10g (9.0.4);
* Oracle JDeveloper 10g: a Java integrated development environment;
Since version 5, Oracle's RDBMS release numbering has used the following codes:
* Oracle5
* Oracle6
* Oracle7: 7.0.16—7.3.4
* Oracle8 Database: 8.0.3—8.0.6
* Oracle8i Database Release 1: 8.1.5.0—8.1.5.1
* Oracle8i Database Release 2: 8.1.6.0—8.1.6.3
* Oracle8i Database Release 3: 8.1.7.0—8.1.7.4
* Oracle9i Database Release 1: 9.0.1.0—9.0.1.5 (patchset as of December 2003)
* Oracle9i Database Release 2: 9.2.0.1—9.2.0.8 (patchset as of April 2007)
* Oracle Database 10g Release 1: 10.1.0.2—10.1.0.5 (patchset as of February 2006)
* Oracle Database 10g Release 2: 10.2.0.1—10.2.0.4 (patchset as of April 2008)
* Oracle Database 11g Release 1: 11.1.0.6—11.1.0.7 (patchset as of September 2008)
* Oracle Database 11g Release 2: 11.2.0.1 (released 2009-09-01)
The version-numbering syntax within each release follows the pattern: major.maintenance.application-server.component-specific.platform-specific.
For example, "10.2.0.1 for 64-bit Solaris" means: 10th major version of Oracle, maintenance level 2, Oracle Application Server (OracleAS) 0, level 1 for Solaris 64-bit.
List of claimed firsts
Oracle Corporation claims to have provided:
* the first commercially-available SQL-based database (1979)
* the first database to support symmetric multiprocessing (SMP) (1983)
* the first distributed database (1986)
* the first database product tested to comply with the ANSI SQL standard (1993)
* the first 64-bit database (1995)
* the first database to incorporate a native JRE (1998)
* the first proprietary RDBMS to become available on Linux (1998)
* the first database to support XML (1999)
Editions
Over and above the different versions of the Oracle database management software, Oracle Corporation subdivides its product into varying "editions" - apparently for marketing and license-tracking reasons. In approximate order of decreasing scale, we find:
* Enterprise Edition (EE) includes more features than the 'Standard Edition', especially in the areas of performance and security. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running 4 or more CPUs. EE has no memory limits, and can utilize clustering using Oracle RAC software.
* Standard Edition (SE) contains base database functionality. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running from one to four CPUs. If the number of CPUs exceeds 4 CPUs, the user must convert to an Enterprise license. SE has no memory limits, and can utilize clustering with Oracle RAC at no additional charge.
* Standard Edition One, introduced with Oracle 10g, has some additional feature-restrictions. Oracle Corporation markets it for use on systems with one or two CPUs. It has no memory limitations.
* Express Edition ('Oracle Database XE'), introduced in 2005, offers Oracle 10g free to distribute on Windows and Linux platforms. It has a footprint of only 150 MB and is restricted to the use of a single CPU, a maximum of 4 GB of user data. Although it can install on a server with any amount of memory, it uses a maximum of 1 GB. Support for this version comes exclusively through on-line forums and not through Oracle support.
* Oracle Database Lite, intended for running on mobile devices. The database located on the mobile device can synchronize with a server-based installation.
Host platforms
Prior to releasing Oracle9i in 2001, Oracle Corporation ported its database product to a wide variety of platforms. More recently Oracle Corporation has consolidated on a smaller range of operating-system platforms.
As of October 2006, Oracle Corporation supported the following operating systems and hardware platforms for Oracle Database 10g:
* Apple Mac OS X Server: PowerPC
* HP HP-UX: PA-RISC, Itanium
* HP Tru64 UNIX: Alpha
* HP OpenVMS: Alpha, Itanium
* IBM AIX5L: IBM POWER
* IBM z/OS: zSeries
* Linux: x86, x86-64, PowerPC, zSeries, Itanium
* Microsoft Windows: x86, x86-64, Itanium
* Sun Solaris: SPARC, x86, x86-64
Database options
Oracle Corporation refers to some extensions to the core functionality of the Oracle database as "database options". As of 2008 such options include:
* Active Data Guard (extends Oracle Data Guard physical standby functionality in 11g)
* Advanced Security (adds data encryption methods)
* Content database (provides a centralized repository for unstructured information)
* Database Vault (enforces extra security on data access)
* Data Mining (ODM) (mines for patterns in existing data)
* In-Memory Database Cache (utilizes TimesTen technology)
* Label Security (enforces row-level security)
* Management Packs (various)
* Oracle Answers (for ad-hoc analysis and reporting)
* Oracle OLAP (adds analytical processing)
* Oracle Programmer (provides programmatic access to Oracle databases via precompilers, interfaces and bindings)
* Partitioning (granularizes tables and indexes for efficiency)
* Real Application Clusters (RAC) (coordinates multiple database servers, together accessing the same database)
* Oracle Real Application Testing (new at version 11g)—including Database Replay (for testing workloads) and SQL Performance Analyzer (SPA) (for preserving SQL efficiency in changing environments)
* Records database (a records management application)
* Oracle Spatial (integrates relational data with geographic information systems (GIS))
* Transparent Gateway for connecting to non-Oracle systems. Offers optimized solution, with more functionality and better performance than Oracle Generic Connectivity.
* Total Recall (optimizes long-term storage of historical data)
* Oracle Warehouse Builder (in various forms and sub-options)
This list is incomplete; you can help by expanding it.
In most cases, using these options entails extra licensing costs.
Suites
In addition to its RDBMS, Oracle Corporation has released several related suites of tools and applications relating to implementations of Oracle databases. For example:
* Oracle Application Server, a J2EE-based application server, aids in developing and deploying applications which utilise Internet technologies and a browser.
* Oracle Collaboration Suite contains messaging, groupware and collaboration applications.
* Oracle Developer Suite contains software development tools, including JDeveloper.
* Oracle E-Business Suite collects together applications for enterprise resource planning (including Oracle Financials), customer relationship management and human resources management (Oracle HR).
* Oracle Enterprise Manager (OEM) used by database administrators (DBAs) to manage the DBMS, and recently in version 10g, a web-based rewrite of OEM called "Oracle Enterprise Manager Database Control". Oracle Corporation has dubbed the super-Enterprise-Manager used to manage a grid of multiple DBMS and Application Servers "Oracle Enterprise Manager Grid Control".
* Oracle Programmer/2000, a bundling of interfaces for 3GL programming languages, marketed with Oracle7 and Oracle8.
Database "features"
Apart from the clearly-defined database options, Oracle databases may include many semi-autonomous software sub-systems, which Oracle Corporation sometimes refers to as "features" in a sense subtly different from the normal usage of the word. For example, Oracle Data Guard counts officially as a "feature", but the command-stack within SQL*Plus, though a usability feature, does not appear in the list of "features" in Oracle's list. Such "features" may include (for example):
* Active Session History (ASH), the collection of data for immediate monitoring of very recent database activity.
* Automatic Workload Repository (AWR), providing monitoring services to Oracle database installations from Oracle version 10. Prior to the release of Oracle version 10, the Statspack facility provided similar functionality.
* Clusterware
* Data Aggregation and Consolidation
* Data Guard for high availability
* Generic Connectivity for connecting to non-Oracle systems.
* Data Pump utilities, which aid in importing and exporting data and metadata between databases
* Database Resource Manager (DRM), which controls the use of computing resources.
* Fine-grained auditing (FGA) (in Oracle Enterprise Edition) supplements standard security-auditing features
* Flashback for selective data recovery and reconstruction
* iSQL*Plus, a web-browser-based graphical user interface (GUI) for Oracle database data-manipulation (compare SQL*Plus)
* Oracle Data Access Components (ODAC), tools which consist of:
o Oracle Data Provider for .NET (ODP.NET)
o Oracle Developer Tools (ODT) for Visual Studio
o Oracle Providers for ASP.NET
o Oracle Database Extensions for .NET
o Oracle Provider for OLE DB
o Oracle Objects for OLE
o Oracle Services for Microsoft Transaction Server
* Oracle-managed files (OMF) -- a feature allowing automated naming, creation and deletion of datafiles at the operating-system level.
* Recovery Manager (rman) for database backup, restoration and recovery
* SQL*Plus, a program that allows users to interact with Oracle database(s) via SQL and PL/SQL commands on a command-line. Compare iSQL*Plus.
This list is incomplete; you can help by expanding it.
Standalone tools
Users can develop applications in Java and PL/SQL using tools such as Oracle JDeveloper, Oracle Forms, or Oracle Reports. Oracle Corporation has started a drive toward 'wizard'-driven environments with a view to enabling non-programmers to produce simple data-driven applications.
Oracle SQL Developer, a free graphical tool for database development, allows developers to browse database objects, run SQL statements and SQL scripts, and edit and debug PL/SQL statements. It incorporates standard and customized reporting.
Other databases marketed by Oracle Corporation
By acquiring other technology in the database field, Oracle Corporation has taken over:
* TimesTen, a memory-resident database that can cache transactions and synchronize data with a centralized Oracle database server. It functions as a real-time infrastructure software product intended for the management of low-latency, high-volume data, of events and of transactions.
* BerkeleyDB, a simple, high-performance, embedded database
* Oracle Rdb, a legacy relational database for the OpenVMS operating system
* MySQL a relational database purchased as part of its immediate previous owner, Sun Microsystems
Use
The Oracle RDBMS has had a reputation among novice users as difficult to install on Linux systems. Oracle Corporation has packaged recent versions for several popular Linux distributions in an attempt to minimize installation challenges beyond the level of technical expertise required to install a database server.
Official support
Users who have Oracle support contracts can use Oracle's MetaLink web site. MetaLink provides users of Oracle Corporation products with a repository of reported problems, diagnostic scripts and solutions. It also integrates with the provision of support tools, patches and upgrades.
The Remote Diagnostic Agent or RDA can operate as a command-line diagnostic tool executing a script. The data captured provides an overview of the Oracle Database environment intended for diagnostic and trouble-shooting. Within RDA, the HCVE (Health Check Validation Engine) can verify and isolate host system environmental issues that may affect the performance of Oracle software.
Database-related guidelines
Oracle Corporation also endorses certain practices and conventions as enhancing the use of its database products. These include:
* Oracle Maximum Availability Architecture (MAA), guidelines on developing high-availability systems
* Optimal Flexible Architecture (OFA), blueprints for mapping Oracle-database objects to file-systems
Oracle Certification Program
Main article: Oracle Certification Program
The Oracle Certification Program, a professional certification program, includes the administration of Oracle Databases as one of its main certification paths. It contains three levels not upto limits.
1. Oracle Certified Associate (OCA)
2. Oracle Certified Professional (OCP)
3. Oracle Certified Master (OCM)
User groups
A variety of official (Oracle-sponsored) and unofficial Oracle User Groups has grown up of users and developers of Oracle databases. They include:
* Oracle Technology Network
* Independent Oracle Users Group
* Geographical/regional user groups
* Product-centric user groups
* Industry-centric user groups
* The Oak Table Network
* Usenet newsgroups
Market position
In the market for relational databases, Oracle Database competes against commercial products such as IBM's DB2 UDB and Microsoft SQL Server. Oracle and IBM tend to battle for the mid-range database market on UNIX and Linux platforms, while Microsoft dominates the mid-range database market on Microsoft Windows platforms. However, since they share many of the same customers, Oracle and IBM tend to support each other's products in many middleware and application categories (for example: WebSphere, PeopleSoft, and Siebel Systems CRM), and IBM's hardware divisions work closely with Oracle on performance-optimizing server-technologies (for example, Linux on zSeries). The two companies have a relationship perhaps best described as "coopetition". Niche commercial competitors include Teradata (in data warehousing and business intelligence), Software AG's ADABAS, Sybase, and IBM's Informix, among many others.
Increasingly, the Oracle database products compete against open-source relational database systems, particularly PostgreSQL, Firebird, and MySQL. Oracle acquired Innobase, supplier of the InnoDB codebase to MySQL, in part to compete better in the open source market. Database products developed on the basis of the open-source model generally cost significantly less to acquire than Oracle systems.
In 2007, competition with SAP AG occasioned litigation from Oracle Corporation.
Pricing
Oracle Corporation offers term licensing for all Oracle products. It bases the list price for a term-license on a specific percentage of the perpetual license price.
Enterprise Edition
As of March 2006, the database that costs the most per machine-processor among Oracle database editions.
Standard Edition
Cheaper: it can run on up to four processors but has fewer features than Enterprise Edition—it lacks proper parallelization,etc; but remains quite suitable for running medium-sized applications.
Standard ONE
Sells even more cheaply, but remains limited to two CPUs. Standard Edition ONE sells on a per-seat basis with a five-user minimum. Oracle Corporation usually sells the licenses with an extra 22% cost for support and upgrades (access to MetaLink—Oracle Corporation's support site) which customers need to renew annually.
Oracle Express Edition (Oracle XE)
An addition to the Oracle database product family (beta version released in 2005, production version released in February 2006), offers a free version of the Oracle RDBMS, but one limited to 4 GB of user data and to 1 GB of RAM (SGA+PGA). XE will use no more than one CPU and lacks an internal JVM. XE runs only on Windows and on Linux, not on AIX, Solaris, HP-UX and the other operating systems available for other editions.
As computers running Oracle often have eight or more processors, the software price can rise into the hundreds of thousands of dollars. The total cost of ownership often exceeds this, as large Oracle installations usually require experienced and trained database administrators to do the set-up properly. Because of the product's large installed base and available training courses, Oracle specialists in some areas have become a more abundant resource than those for more exotic databases. Oracle frequently provides special training offers for database-administrators.
On Linux, Oracle's certified configurations include mostly commercial Linux distributions (Red Hat Enterprise Linux 3 and 4, SuSE SLES8 and 9, Asianux) which can cost in a range from a few hundred to a few thousand USD per year (depending on processor architecture and the support package purchased).
The Oracle database system can also install and run on freely-available Linux distributions such as the Red Hat-based Centos,or Debian-based systems.
Monday, December 21, 2009
Oracle Upgradation from 10g to 11g
Oracle 11g Database software must be installed in new ORACLE_HOME
For some database version direct upgrade to 11g is NOT supported
7.3.3 (or lower) -> 7.3.4 -> 9.2.0.8 -> 11.1
8.0.5 (or lower) -> 8.0.6 -> 9.2.0.8 -> 11.1
8.1.7 (or lower) -> 8.1.7.4 -> 9.2.0.8 -> 11.1
9.0.1.3 (or lower) -> 9.0.1.4 -> 9.2.0.8 -> 11.1
9.2.0.3 (or lower) -> 9.2.0.8 -> 11.1
Direct upgrade to 11g is supported from following version
9.2.0.4 and higher -> 11.1
10.1.0.2 and higher -> 11.1
10.2.0.1 and higher -> 11.1
Tools and methods to upgrade database
1. DBUA (DataBase Upgrade Assistant) Utility - GUI
2. Manual Upgradeusing SQL scripts and Utilities - Command line tool (catupgrd.sql..)
Top level steps for Oracle Database 11g upgarde
1. Prepare Upgrade to 11g Database
2. Backup existing database software and database
3. Analyze the database using Pre-Upgrade Information Tool
4. Install Oracle 11g software in new ORACLE_HOME
5. Run Pre-upgrade information tool
SQL>spool upgrd_info.sql
SQL>@?/rdbms/admin/utlu111i.sql (check output and modify).
6. Check Invalid objects.
SQL>select object_name,owner,object_type from all_objects where status like 'INVALID';
7. Check version and status of all database components.
SQL>select comp_name,version,status from dba_registry;
8. Change compatibility in init.ora
9. Startup upgrade
SQL>spool upgrade.log
SQL>@?/rdbms/admin/catupgrd.sql
10.Run post-upgrade status tool provides a summary of the upgrade.
SQL>@?/rdbms/admin/utlu111s.sql
For some database version direct upgrade to 11g is NOT supported
7.3.3 (or lower) -> 7.3.4 -> 9.2.0.8 -> 11.1
8.0.5 (or lower) -> 8.0.6 -> 9.2.0.8 -> 11.1
8.1.7 (or lower) -> 8.1.7.4 -> 9.2.0.8 -> 11.1
9.0.1.3 (or lower) -> 9.0.1.4 -> 9.2.0.8 -> 11.1
9.2.0.3 (or lower) -> 9.2.0.8 -> 11.1
Direct upgrade to 11g is supported from following version
9.2.0.4 and higher -> 11.1
10.1.0.2 and higher -> 11.1
10.2.0.1 and higher -> 11.1
Tools and methods to upgrade database
1. DBUA (DataBase Upgrade Assistant) Utility - GUI
2. Manual Upgradeusing SQL scripts and Utilities - Command line tool (catupgrd.sql..)
Top level steps for Oracle Database 11g upgarde
1. Prepare Upgrade to 11g Database
2. Backup existing database software and database
3. Analyze the database using Pre-Upgrade Information Tool
4. Install Oracle 11g software in new ORACLE_HOME
5. Run Pre-upgrade information tool
SQL>spool upgrd_info.sql
SQL>@?/rdbms/admin/utlu111i.sql (check output and modify).
6. Check Invalid objects.
SQL>select object_name,owner,object_type from all_objects where status like 'INVALID';
7. Check version and status of all database components.
SQL>select comp_name,version,status from dba_registry;
8. Change compatibility in init.ora
9. Startup upgrade
SQL>spool upgrade.log
SQL>@?/rdbms/admin/catupgrd.sql
10.Run post-upgrade status tool provides a summary of the upgrade.
SQL>@?/rdbms/admin/utlu111s.sql
Friday, December 18, 2009
Oracle: Recover a deleted datafile without backup even your DB in no archive mode from unix/linux when database is still up
How to use Linux behavior to recover an accidentally delete file when the database is still open.
On Unix/Linux, when a file is deleted, but a process still has the file open, the file is still there in the filesystem, and only the inode is removed.
But the process can continue to use its file handle, and the file can also be accessible under /proc//fd .
In the following example, we use that behaviour to recover a lost datafile after is has been dropped from the os (with rm) but the datafile is still open by the background processes.
First, we create a tablespace, and populate a table in it.
SQL> REM we create a tablespace:
SQL> create tablespace TEST_RM datafile '/oradata/tmp/test_rm.dbf' size 10M;
Tablespace created.
SQL> REM we create a table in it:
SQL> create table KHAN_TEST tablespace test_rm as select * from dba_objects;
Table created.
SQL> REM we check that table data is accessible:
SQL> select count(*) from KHAN_TEST;
COUNT(*)
----------
12708
SQL> exit
Disconnected from Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
Then, we drop the datafile from unix prompt.
here is the datafile
ls -l /oradata/tmp/test_rm.dbf
-rw-r----- 1 oracle dba 10493952 Sep 26 14:25 /oradata/tmp/test_rm.dbf
we 'accidently' drop the datafile
rm /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
ls: /oradata/tmp/test_rm.dbf: no such file or directory
Here the datafile is lost.
Now we connect again.
sqlplus / as sysdba
Connected to:
Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
SQL> REM and we check if table data is accessible:
SQL> select count(*) from KHAN_TEMP;
select * from khan_temp
*
ERROR at line 1:
ORA-01116: error in opening database file 5
ORA-01110: data file 5: '/oradata/tmp/test_rm.dbf'
ORA-27041: unable to open file
Linux Error: 2: No such file or directory
Additional information: 3
The datafile is lost and data is not accessible.
However, the datafile should still have an open file descriptor by an oracle background process
we check the dbwriter pid:
ps -edf | grep dbw
oracle 2661 1 0 Sep26 ? 00:00:06 xe_dbw0_XE
oracle 7044 7037 0 14:40 pts/1 00:00:00 /bin/bash -c ps -edf | grep dbw
oracle 7046 7044 0 14:40 pts/1 00:00:00 grep dbw
and we check its opened file descriptors for our file:
ls -l /proc/2661/fd | grep test_rm
lrwx------ 1 oracle dba 64 Sep 26 14:02 66 -> /oradata/tmp/test_rm.dbf (deleted)
here it is:
ls -l /proc/2661/fd/66
lrwx------ 1 oracle dba 64 Sep 26 14:02 /proc/2661/fd/66 -> /oradata/tmp/test_rm.dbf (deleted)
In some other unix, lsof may be needed to map the file descriptor with the deleted file name
first we set a symbolic link so that oracle can see it as it was before the delete:
ln -s /proc/2661/fd/66 /oradata/tmp/test_rm.dbf
here data is accessible, but that will be lost if dbwriter closes it file handle (i.e if the database is closed)
However we can now set the tablespace read only so that it is checkpointed, and no writes occurs on it.
SQL> alter tablespace TEST_RM read only;
Tablespace altered.
We can now copy the file safely.
then we drop the symbolic link:
rm /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
ls: /oradata/tmp/test_rm.dbf: No such file or directory
and we can now copy the file
cp -p /proc/2661/fd/66 /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
-rw-r----- 1 oracle dba 10493952 Mar 26 14:54 /oradata/tmp/test_rm.dbf
And datafile is now available again.
SQL> REM we have it back, lets put the tablespace back in read/write
SQL> alter tablespace test_rm read write;
Tablespace altered.
SQL> REM and we check data is still there:
SQL> select count(*) from FRANCK;
COUNT(*)
----------
12708
Note:This is not to be used like that in production. This is unsupported and may behave differently on different unix/linux or oracle versions.
On Unix/Linux, when a file is deleted, but a process still has the file open, the file is still there in the filesystem, and only the inode is removed.
But the process can continue to use its file handle, and the file can also be accessible under /proc/
In the following example, we use that behaviour to recover a lost datafile after is has been dropped from the os (with rm) but the datafile is still open by the background processes.
First, we create a tablespace, and populate a table in it.
SQL> REM we create a tablespace:
SQL> create tablespace TEST_RM datafile '/oradata/tmp/test_rm.dbf' size 10M;
Tablespace created.
SQL> REM we create a table in it:
SQL> create table KHAN_TEST tablespace test_rm as select * from dba_objects;
Table created.
SQL> REM we check that table data is accessible:
SQL> select count(*) from KHAN_TEST;
COUNT(*)
----------
12708
SQL> exit
Disconnected from Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
Then, we drop the datafile from unix prompt.
here is the datafile
ls -l /oradata/tmp/test_rm.dbf
-rw-r----- 1 oracle dba 10493952 Sep 26 14:25 /oradata/tmp/test_rm.dbf
we 'accidently' drop the datafile
rm /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
ls: /oradata/tmp/test_rm.dbf: no such file or directory
Here the datafile is lost.
Now we connect again.
sqlplus / as sysdba
Connected to:
Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
SQL> REM and we check if table data is accessible:
SQL> select count(*) from KHAN_TEMP;
select * from khan_temp
*
ERROR at line 1:
ORA-01116: error in opening database file 5
ORA-01110: data file 5: '/oradata/tmp/test_rm.dbf'
ORA-27041: unable to open file
Linux Error: 2: No such file or directory
Additional information: 3
The datafile is lost and data is not accessible.
However, the datafile should still have an open file descriptor by an oracle background process
we check the dbwriter pid:
ps -edf | grep dbw
oracle 2661 1 0 Sep26 ? 00:00:06 xe_dbw0_XE
oracle 7044 7037 0 14:40 pts/1 00:00:00 /bin/bash -c ps -edf | grep dbw
oracle 7046 7044 0 14:40 pts/1 00:00:00 grep dbw
and we check its opened file descriptors for our file:
ls -l /proc/2661/fd | grep test_rm
lrwx------ 1 oracle dba 64 Sep 26 14:02 66 -> /oradata/tmp/test_rm.dbf (deleted)
here it is:
ls -l /proc/2661/fd/66
lrwx------ 1 oracle dba 64 Sep 26 14:02 /proc/2661/fd/66 -> /oradata/tmp/test_rm.dbf (deleted)
In some other unix, lsof may be needed to map the file descriptor with the deleted file name
first we set a symbolic link so that oracle can see it as it was before the delete:
ln -s /proc/2661/fd/66 /oradata/tmp/test_rm.dbf
here data is accessible, but that will be lost if dbwriter closes it file handle (i.e if the database is closed)
However we can now set the tablespace read only so that it is checkpointed, and no writes occurs on it.
SQL> alter tablespace TEST_RM read only;
Tablespace altered.
We can now copy the file safely.
then we drop the symbolic link:
rm /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
ls: /oradata/tmp/test_rm.dbf: No such file or directory
and we can now copy the file
cp -p /proc/2661/fd/66 /oradata/tmp/test_rm.dbf
ls -l /oradata/tmp/test_rm.dbf
-rw-r----- 1 oracle dba 10493952 Mar 26 14:54 /oradata/tmp/test_rm.dbf
And datafile is now available again.
SQL> REM we have it back, lets put the tablespace back in read/write
SQL> alter tablespace test_rm read write;
Tablespace altered.
SQL> REM and we check data is still there:
SQL> select count(*) from FRANCK;
COUNT(*)
----------
12708
Note:This is not to be used like that in production. This is unsupported and may behave differently on different unix/linux or oracle versions.
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