Oracle Unleashed- P6

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Oracle Unleashed- P6

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Oracle Unleashed- P6: When I first started using Oracle many years ago, it was possible to know the database and the tools available. With the rash of recent releases of different options for the database and the spate of new tools, only people who wear their underpants over their trousers will be able to know everything there is to know about the Oracle products.

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1. Enter table name or . if done: dept Enter table name or . if done: . The last example is from full database mode. Import entire export file (yes/no): yes >Y User Mode The user method of Import enables you to import tables that belong to a specific user. This can also be combined with the table mode to import specific tables from a specific schema. This is important because Import attempts to create the tables in the current schema's default tablespace if the schema specified in the export file does not exist. This can work to your advantage if you need to move tables from one schema to another. Table Mode You usually use table mode to import a table or a list of tables, rather than all tables in the export file. If a user has access to other schema, he can import tables from other schema by qualifying with the schema name. The default is to import all tables in the schema of the user doing the import. Full Database Mode The full database option of Import does not quite work the same way as the full database option of Export. If you specify the full database option in Export, the entire database is exported, and to import the entire file, you must have the role IMP_FULL_DATABASE assigned to you. If the export file is a user export or table export, the entire export file is imported (whatever is in it), and you do not need to have the role IMP_FULL_DATABASE assigned to you. Interactive Versus Command Line Both Import and Export can operate in command-line mode and in interactive mode. Both modes have their advantages, but Oracle recommends that you use the command-line mode with a parameter file. The two modes are outlined in this section. I'm sure you will find good reasons for using both in your own situation. Interactive Method The interactive method is an easy way to import data from export files, but you do not have all the options of the parameter or command-line method. For example, you cannot create an index file. The interactive prompts might change depending on the response to previous prompts. The interactive prompts also have the benefit of showing the prechosen defaults. To use Import in the interactive mode, type imp or imp USERID=userid/password at the command line. The interactive method continues to exist only for backward compatibility. An interactive import might resemble the following: /usr/local/p3016dk > imp scott/tiger Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
2. Import: Release 7.1.4.1.0 - Production on Sun Oct 1 10:12:54 1995 Copyright (c) Oracle Corporation 1979, 1994. All rights reserved. Connected to: Oracle7 Server Release 7.1.4.1.0 - Production Release With the distributed and parallel query options PL/SQL Release 2.1.4.0.0 - Production Import file: ./expdat.dmp > scott.dmp Enter insert buffer size (minimum is 4096) 30720> Export file created by EXPORT:V07.01.04 List contents of import file only (yes/no): no > Ignore create error due to object existence (yes/no): yes > n Import grants (yes/no): yes > y Import table data (yes/no): yes > y Import entire export file (yes/no): yes > y Command-Line Method The same import can be accomplished by entering the following command-line options. imp USERID=scott/tiger FILE=scott.dmp ignore=N Import responds with the following: Import: Release 7.1.4.1.0 - Production on Sun Oct 1 10:19:12 1995 Copyright (c) Oracle Corporation 1979, 1994. All rights reserved. Connected to: Oracle7 Server Release 7.1.4.1.0 - Production Release With the distributed and parallel query options PL/SQL Release 2.1.4.0.0 - Production Export file created by EXPORT:V07.01.04 . importing SCOTT's objects into SCOTT . . importing table "BONUS" 0 rows imported . . importing table "CUSTOMER" 9 rows imported . . importing table "DEPT" 4 rows imported . . importing table "DUMMY" 1 rows imported Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
3. . . importing table "EMP" 14 rows imported . . importing table "EXECUTABLES" 0 rows imported . . importing table "FALL5" 30 rows imported . . importing table "ITEM" 64 rows imported . . importing table "ORD" 21 rows imported . . importing table "PRICE" 17 rows imported Import terminated successfully without warnings. Import Parameters That Affect Performance As with Export, Import also has several parameters that affect performance. This section lists the parameters that affect performance the most along with an explanation of how they work and how to use them. BUFFER The BUFFER parameter for Import works the same way as the BUFFER parameter in Export. For the most part, you can specify a large value for best results. COMMIT The COMMIT parameter defaults to N, but if do not have large rollback segments to use (at least as large as the largest table), set this option to Y. If you set COMMIT to Y, Import commits every time the buffer fills and the array is inserted. The only significant performance gain you will notice is when your import fails because of a rollback issue and you must redo an import. LOG Quite simply, always use the LOG parameter so you can review the log file and effectively fix anything that went wrong. How Objects Import Objects are created in a specific order as the import progresses. The important thing to remember is that Import first creates the table and then loads the data for each table. Import creates all the indexes on the tables after it loads all the table data. Finally, Import enables all the table constraints and triggers. In some situations, the table constraints can cause interesting results (usually undesirable). If you are in the habit of precreating the tables before the import as I am, you know you'd better disable the constraints before importing. Reenable the constraints when the import is finished. Don't forget! Tables Import first creates the table definitions and then loads the data. Import creates all the indexes for the table and then creates and enables the constraints and database triggers. The important thing to note is that all the tables are loaded and all of the indexes are created a table at a time. When the tables are finished, Import creates and reenables all the table constraints. Stored Procedures Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
4. Packages, functions, and stored procedures are imported without updating the time stamp. This enables Oracle to use the objects without recompiling them. Snapshots Snapshots are exported quite uneventfully. Oracle exports and imports the master table, the master table trigger, the snapshot log (if you are using one), and the snapshot itself, similar to exporting and importing tables and database triggers. If you are using a snapshot log, only the snapshot log definition is exported and imported. What this means to you is that the first fast refresh that is attempted on that snapshot will fail. Plan on a complete refresh of all of the imported snapshots after the import is complete. Importing and Exporting with Personal Oracle7 My world has not been the same since Oracle introduced Personal Oracle7. I have been able to develop complete applications on my PC at home. Although I do not have a PC platform that compares with our Sequent, HP, or DG platforms, I can't resist the desire to develop applications on it. I haven't yet used Personal Oracle7 for any production applications, but I am sure many people have. All of us who have had the pleasure of experiencing Personal Oracle7 will agree that the Windows front end on the Import and Export utilities is a nice addition to the old familiar utilities. I think that many Personal Oracle7 users like me are developing applications. I find myself exporting tables from the true development platforms at the job site and then importing them into my PC database so I can develop whenever and whatever I like. Using the Personal Oracle7 version of Import and Export is quite a bit different from the old standards. Personal Oracle7 has a nice GUI interface that is hard to beat. It still works internally the same way as the character versions and outputs files that you can transfer to other Oracle instances. The main difference in Personal Oracle7 is the Windows front end. Figure 9.1 shows the Export utility in Personal Oracle7; the title bar has the caption Database Exporter. The first thing you notice is that parameters are represented by text boxes, checkboxes, or pull-down lists. Figure 9.2 shows the advanced options. The advanced options are Record Length (RECORDLENGTH), Buffer Size (BUFFER), Record Export in System Data (RECORD), Keep Components Consistent (CONSISTENT), Compress When Imported (COMPRESS), Log File (LOG) Increment Type (INCTYPE), and Statistics Type (STATISTICS). The other Export parameters follow similar translations. Figure 9.1. Personal Oracle's Export utility. Figure 9.2. Export utility advanced options. Figure 9.3 and 9.4 show the Database Importer and the advanced options available. The Database Importer closely resembles the Exporter's look and feel. I do not go into detail because its functionality is fairly obvious. Figure 9.3. The Import utility. Figure 9.4. Import utility advanced options. Import and Export Hints and Tips You can use Import and Export for tasks other than just backing up data. I often use Import and Export for several other constructive reasons, and this section outlines a few of the best hints and tips. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
5. Create an Index File Import can create what is known as an index file. This is a SQL script of not only the creation scripts for the indexes in the export file but also creation scripts for the other database objects in the export file. All the lines in the file except for the index creation scripts are commented out. The commented-out code contains creation scripts for the remaining objects in the export file. With some editing, you can create a script that can be used to precreate all the tables and indexes and so on. This is often necessary if you use the parameter COMPRESS=Y. Adjusting Storage Parameters Using the parameter COMPRESS=Y rewrites the original storage parameters so that the table or index resides on one contiguous extent. Compressing the extents is a good idea as long as you actually have the contiguous extents available. I suggest precreating the tables and indexes with your edited INDEXFILE. This ensures that you can actually create the objects. Of course, if any table or index fails to create, you can adjust the initial and next extents in the INDEXFILE and attempt to create the table again. This is also a good time to adjust the PCTFREE and PCTUSED and the TABLESPACE parameters (or any of the other table parameters) in the table and index creation statements. I highly recommend that you study and adjust the size requirement if necessary at this time, especially if the storage parameters are set to their defaults. I don't go into great detail, but here are some good places to start if you have a mess of default storage parameters: Parameter Defaults to Set to PCTFREE 10% 5-20% PCTUSED 40% 55-90% PCTINCREASE 50% 0% INITIAL 10240 or 2048 All data in one extent plus some growth if possible NEXT 10240 or 20480 25% up to the size of INITIAL There are other storage parameters, but these five are typically the most important to me. Reorganizing Data Users own tables, indexes, and other objects. The tables and indexes users create reside in tablespaces. If you were to export a user's tables, drop them, and then import them, they end up in the user's default tablespace again. If you need to move tables from one tablespace to another, you export the tables and change the user's default tablespace and quotas to another tablespace that you want to contain the tables. Then, when you reimport the tables, they are created in the new default tablespace. Reducing Database Fragmentation When a database has many small blocks of free space, you should export it with the FULL=Y parameter. Recreate the database and then do a full database import. Tablespaces also need similar help. You should plan carefully where and how many data files a tablespace has. To recreate the tablespace, export all the objects, using the nifty script I provided if Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
6. you like. Drop the tablespace including its contents. Recreate the tablespace and then import the fresh new tablespace. Migrating from Version 6 to Oracle7 Import can read export files from Version 6 Oracle. You could use this function to migrate by exporting the Version 6 database and then recreating the database in Oracle7. Some data type changes occurred after Version 6; the old Version 6 CHAR data type changed to VARCHAR2. Import handles this conversion for you. If you're wondering who is going to change all your table creation scripts from the old CHAR data type to VARCHAR2, try using the INDEXFILE parameter explained earlier. Oracle7 provides vastly expanded integrity constraints, and the SQL syntax is slightly different from Version 6. All the existing constraints are exported, but only the NOT NULL constraint is imported and enabled. Importing Tables with LONG and LONG RAW Data Types Did you know it is possible to export a table with extremely large columns (LONG data types can be up to 2 GB in length) only to discover that they cannot be imported? It hasn't happened to me, but Oracle reports that this could happen. The reason is that Export can break up the long data, but Import must read the data into contiguous memory to import. If you do not have enough memory, the import fails. Summary Import and Export not only provide data recovery, but they have quite a few database management uses as well. I am sure you will find yourself using Import and Export often to keep your database tuned well by reducing fragmentation and enabling yourself to change the storage parameters of tables and their locations or owners. Whatever task you choose for Import and Export, you will find them to be a stable pair of utilities that are easy to use. Previous Next TOC Home Page Page Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
10. involved in a distributed failure. The distributed option is also required if you wish to create Snapshots which are copies of tables (usually) on other databases which are automatically replicated to your database at user defined intervals. In addition, the distributed option includes the capability to call procedures, functions, and packages, which have been defined on remote databases. So, in theory though not very practically, you can hold the database procedures, functions, and packages on one central database, and all other databases can make calls to this central copy of the code. Parallel Server Option The Oracle parallel server option allows more than one instance to access the same set of database files. This option ensures, for example, that if a row is locked on one instance that it is reported as locked on any other instances accessing the same database. The parallel server option is be used where more than one processor is available (either in the same machine or in different machines which have been clustered together). Parallel Query Option The parallel query option improves performance of full-table scans. This allows a large query to be executed by multiple processes so that many processes can be used to perform parts of the query, with the results being merged together automatically. In addition, the parallel query option allows creation of indexes in parallel. This is similar in concept to the parallel query mentioned earlier, where more than one process can be used to build different parts of the index, and the results from each of these processes is merged together. The parallel query option normally runs on those machines where more than one processor has been installed so that you can use the processing power of more than one processor to perform the heavy-load work which you require. Trusted Oracle Trusted Oracle provides additional security than what is available with the base product and is usually found either in military type applications or those where a high level of security is required. This gives, for example, the ability to control which rows are accessible to which users. This is not easily done with the base product. Tip: Use the v$version view, which is accessible to the system user, to see which versions of the Oracle product you have installed. In addition, the v$compatseg view shows which version of the Oracle server software introduced some of the new releases. Installation Preparation The actual process of installing the Oracle software and creating the first database is relatively easy on most platforms because you can follow the menu options; however, preparation before the actual install pays dividends in the long run. One of the first things to consider is the amount of disk space required both for the software and for the database itself. In addition, the locations of the program files, database files, redo logs, and control files should be carefully considered so that disk contention does not occur. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
11. The amount of storage required for the software varies from platform to platform—the Oracle installation and User's Guide manual for your platform should be able to give you an idea for the amount of storage required. The amount of memory required for Oracle will be split into the memory required for the Oracle software to load (much of which is re-entrant code that can be used at the same time by more than one process), the common memory areas (such as the SGA), and the private memory areas (such as the PGA for each connection to the database), as well as memory for the client programs which are executing. Though, this may be on a different machine than the one on which the database server is being run. The default memory allocations (especially for the common SGA area) is not sufficient for most databases. In addition, some operating system specific issues need to be addressed (such as the number of semaphore sets in UNIX)—most of which will be detailed in the installation and user's guide manual. Installing the Software Most platforms have a menu driven installation script or, even better, an installation program that makes the installation a one-stop point-and-click operation, such as the program for installing the Oracle software on the Microsoft Windows platform. Because dependencies exist between different components of the Oracle software, the menu first prompts for the components of software to be installed and works out the dependencies between the different components so that all required components are installed. On some platforms, it may be necessary to create an operating system account with a high-level of privileges which will be used to install the software (usually called Oracle7). The operations of connecting as internal, starting up the instance, shutting down the instance, and creating a database are all privileged operations. They can all be performed from within the SQL*DBA tool (or from the server manager tool if that is available on your platform). As a result, your operating system account needs to have the necessary operating system privileges in order to perform these operations (UNIX groups on UNIX, or process rights on VMS, for example). The way that Oracle determines whether these privileges are in effect is different from platform to platform. At the time of this writing there is no check to ensure that you only install the products for which you are licensed, or that you do not exceed the number of users for which you've bought the license for. Use the v$license view to determine whether you are exceeding the number of users for which you're licensed. Directory Structure For those platforms where a hierarchical directory structure exists, the Oracle default home directory has a name such as "Oracle7," and below this you'll find many subdirectories—usually one for each product being installed. Within each of these product subdirectories, further subdirectories exist for things such as the install scripts, demo files, and so on. The directory structure underneath the Oracle home directory should not be changed—Oracle needs to know Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 12. where to find the different files for the software being installed. For those platforms that support it, an operating system environment variable exists to define where the starting location is for the Oracle software ($ORACLE_HOME for UNIX, ORA_ROOT for VMS and the ORACLE.INI file for the MS Windows platform). Once this environment variable exists, Oracle can work out the locations of the subdirectories and gain access to the files it requires. It is also possible on some platforms to install many different versions of the Oracle software. Operating System Specifics In this section, we highlight some points for three of the major platforms for Oracle. UNIX In addition to an installation and user's guide manual being provided for your platform, there is also a generic UNIX technical reference guide which applies to all UNIX platforms on which Oracle can be run. This should be read in conjunction with the installation and user's guide before starting the install. The $ORACLE_HOME environment variable is used to locate the home directory for the Oracle software, and the$ORACLE_SID environment variable is used to determine which instance ID the user process will connect into. The PATH environment variable should include the $ORACLE_HOME/bin directory so that you can access the various Oracle components. One of the options available for the UNIX platform is to allow Oracle to use raw disk devices—essentially this means that the Oracle software can bypass the buffer manager for the disks and access the disk drives directly giving an increase in performance. However, you should ensure that the necessary UNIX expertise is on-hand to manage raw disk devices—something that is not to be considered for those sites new to UNIX and new to Oracle. VMS The ORA_ROOT logical is used to point to the location of the home directory for the Oracle software. In addition, the ORA_SID symbol is used to determine the instance identifier of the instance to which user processes will connect. MS Windows This is nowadays one of the easiest platforms on which to install the Oracle tools and software. The ORACLE.INI file is used to set the various parameters used by Oracle. The parameters ending with path control where the Oracle software on the PC attempts to find the Oracle software. The default location of the database server machine, the network protocol used to connect that machine, and the instance identifier used when a connection is made to that machine, can be given by the LOCAL parameter in the INIT.ORA file. Summary In this chapter, you have seen an overview of some of the things to consider when installing the Oracle software. This is one of the areas where major differences exist between different platforms. As mentioned earlier, you refer to the installation and user's guide manual for your platform to learn the specifics for your platform. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 13. Previous Next TOC Home Page Page Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 14. Previous Next TOC Home Page Page q 11 r Managing the Database s The Parameter File: INIT.ORA s The Oracle SID s Creating a New Database s The First Objects Created s Startup and Shutdown s Startup Stages s Shutdown Stages s The Data Dictionary s Core System Tables s Data Dictionary Views s Dynamic Performance Tables s Other Data Dictionary Views s Redo Logs s Creating, Altering, and Dropping Redo Logs s Multiplexing Redo Logs s Control Files s Multiplexing Control Files s Trace and Alert Files s Database Modes s NOARCHIVELOG Mode s ARCHIVELOG Mode s Changing the Mode of the Database s Useful Data Dictionary Views s Summary 11 Managing the Database In this chapter, you learn how to perform the following tasks: q Make a new Oracle database q Manage the instance by bringing the instance up and down q Obtain information from the Oracle system tables q Modify the number of control and redo log files The Parameter File: INIT.ORA An instance is the set of background processes and the memory structures that Oracle uses. Every instance must have a parameter file, known as the INIT.ORA file, from which it retrieves the parameters that it uses to run and the mode of Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 15. the database. This parameter file is used by the Oracle SQL*DBA tool when the instance is first started. Once the instance has been started, the parameter file is not used again until the next time the instance is started. The parameter file must be on the same machine as the SQL*DBA tool. INIT.ORA parameter files are used to specify q Amount of storage allocated for the Oracle memory structures q Which rollback segments to use for the instance q National language settings q Settings for running Oracle in parallel server mode q Which database and control file to use q When to issue checkpoints q Limits for database control structures q Which non-mandatory background processes to initialize The file is given the generic name INIT.ORA, but the Oracle instance identifier is usually part of the filename. The name can be any filename, but it usually begins with INIT. The parameter file is an ordinary text file, which you modify using any character-based operating system text editor. The parameters can be included in any order, and they can be specified in upper, lower, or mixed case. Even though the parameters can be included in mixed case, the names of operating system files must be specified according to the operating system's rules for file naming. In UNIX, for example, a filename must be specified exactly as it appears on the file system. You specify over 130 parameters. Most of them are common to all the platforms on which Oracle runs. The number of the parameters increase from one release of the Oracle RDBMS software to the next. An example parameter file comes with the Oracle software; its default name is INIT.ORA. You can use this file could to run your instance, although you might have to adjust the parameters manually to obtain optimal performance. It is possible to many parameter files for the same instance, although only one is used at a time for the instance startup. If you want to use another set of parameters for the run, you must shut down and restart the instance. Many parameters have a minimum value. If they are set below the minimum value, the Oracle instance does not start up. The values of some parameters are derived from settings in other parameters. Normally, you do not need to set them. There are even some parameters that you should not set unless the Oracle support desk instructs you to set them. Appendix A of the Oracle7 Server Administrator's Guide describes all the different parameters. Use one parameter file for the instance for normal online operations during the day. At night, use a parameter file that optimizes performance for a batch job. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 16. In the INIT.ORA file, the only parameter that is mandatory is the CONTROL_FILES parameter, which names one or more control files to be used for the instance. This control files are used during instance startup to determine the names and locations of the database and redo log files. Table 11.1 describes additional parameters for the INIT.ORA file. Table 11.1. Important INIT.ORA parameters. Parameter Name Description Must be set to TRUE to enable auditing rows to be inserted, even if the auditing facility has AUDIT_TRAIL been set up by issuing the AUDIT SQL command. Controls the directory location where the trace files from the Oracle background processes BACKGROUND are written. The alert file, which records significant database events and messages, is also _DUMP_DEST written to this location. You can delete the trace and alert files without affecting the performance of the database. Controls whether the Oracle CKPT background process is to be run. By running the CKPT CHECKPOINT_ process, load is decreased from the LGWR process in updating the database file headers PROCESS whenever a checkpoint occurs. Names one or more control files to be used for this instance. Control files are used during CONTROL_FILES instance startup to determine the name and location of the database and redo log files. Specifies the number of Oracle database blocks to cache in the database buffers area of the DB_BLOCK_BUFFERS SGA. The default value of 32 is too small for all but test databases. Specifies the size of each Oracle block in the database files. Set this parameter when you DB_BLOCK_SIZE first create the database and then do not alter it. Specifies the maximum number of DML locks that can be taken out by the instance. There DML_LOCKS is one DML lock for each user for each table undergoing an INSERT, UPDATE, or DELETE operation at any time for the instance. Specifies the name of the sql files to be executed when the database is created. These files are typically the Oracle-supplied files used to create the data dictionary, the views on the INIT_SQL_FILES data dictionary, and views that enable the export and import utilities to run. After these files have been run during the CREATE DATABASE operation, they are never executed again. LICENSE_MAX_ Controls the maximum number of user sessions that can be connected to the Oracle SESSIONS database at any time. Controls the location to which the archived redo log files are written if the database runs in LOG_ARCHIVE_DEST ARCHIVELOG mode. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 17. Controls the naming format of the archived files if the database is running in LOG_ARCHIVE_ ARCHIVELOG mode. That way, the redo log sequence number, instance thread number, or FORMAT a fixed string can be inserted into the filename. Specifies the size of the redo log buffer in the SGA into which all changes are recorded LOG_BUFFERS from all transactions on the instance. Used to specify whether a checkpoint should occur earlier than the default time of a redo LOG_ log file switch. This should not normally be set for most systems, because more frequent CHECKPOINT_ checkpointing incurs extra system overhead in writing out the changed database blocks in INTERVAL the database buffer cache in the SGA. Controls the amount of time to wait before issuing a checkpoint on the database. For LOG_CHECKPOINT example, if this parameter is set to 1800 seconds (30 minutes), a checkpoint is performed _TIMEOUT every 30 minutes, even if no activity has occurred on the system in the period. Specifies the maximum size of any trace files generated. If you use the trace facility to trace MAX_DUMP large amounts of work, use this parameter to limit how much trace information can be _FILE_SIZE produced. Specifies the default mode for the Oracle optimizer, which determines the execution plan for a SQL statement. The Oracle6 method is RULE, which means that the optimizer does OPTIMIZER_MODE not take account of any statistics that were gathered on tables by using the ANALYZE command. The default value, CHOOSE, uses statistics if they exist. Otherwise, it defaults to the rule based on the optimization method. Specifies the proxy login. The Oracle user name defaults to the operating system user name OS_AUTHENT prefixed by OPS$. You can control the password by using this parameter. The default on _PREFIX most platforms is OPS$, but you can change it to any prefix or even NULL. Controls the maximum number of operating system processes that can connect to the Oracle PROCESSES database through this instance, which includes the background processes. Four background processes are mandatory, and the instance cannot start without them. Must be set to TRUE to enforce checking of resource limits if system resources are RESOURCE_LIMIT controlled through database profiles assigned to Oracle users. To set this parameter online, use the ALTER SYSTEM command. Contains the names of private rollback segments that the instance should use for storing the before-image of any changes made to the database. Rollback segments not mentioned here can still be activated by using the ALTER ROLLBACK SEGMENT command. If no ROLLBACK_ rollback segments are activated, the SYSTEM rollback segment—normally reserved for SEGMENTS recording changes made to the Oracle data dictionary—is used for recording the before- image of the Oracle data blocks. If more than one instance is using the Oracle database, they cannot use the same rollback segments. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 18. Specifies the number of sequence objects to cache in the SGA for generating unique SEQUENCE_CACHE_ numbers using sequences. The sequences must have been created with the CACHE ENTRIES parameter specified as part of the CREATE SEQUENCE statement. Specifies the size of the shared pool area in the SGA that is used to hold the data dictionary SHARED_POOL_SIZE cache, cursors for SQL statements, and PL/SQL code units. Sets the low threshold for the data blocks in an Oracle table. Tables with Oracle data blocks below this limit are read into the SGA completely when you perform a full table scan on SMALL_TABLE_ them. If a table has more data blocks than this limit, the full table access of the table uses THRESHOLD only a portion of the lower part of the database buffers cache of the SGA. This ensures that active blocks in the SGA from other tables are not removed from memory when a full table scan is performed on a large table. Turns on the trace facility for the instance when set to TRUE. With tracing on, execution plans and statement performance can be determined by formatting the trace files produced SQL_TRACE with the TKPROF utility. Timing information is provided only if the TIMED_STATISTICS parameter is also set to TRUE. Determines whether timing information is recorded in the trace files when tracing is enabled TIMED_STATISTICS for the instance or for user sessions. USER_DUMP_DEST Determines the location of user process trace files produced when tracing is enabled for the instance or for user sessions. Table 11.1 does not describe all the parameters in the INIT.ORA file. Refer to Appendix A of the Oracle7 Server Administrator's Guide for descriptions of the all parameters. Use the IFILE parameter to name a file that contains a common set of parameters for all the instances running on the machine. To see the parameters that the current instance is using, enter the following in SQL*DBA: SQLDBA> SHOW PARAMETERS You can also see only those parameters that contain a given string. For example, SQLDBA> SHOW PARAMETERS buffer shows all the parameters that contain the string buffer. To see a list of the parameters when the instance first comes up, include the word LIST in the first line of the INIT.ORA file. To access the parameters from any Oracle tool, run a select operation against the v$parameter table, as in Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
19. SQLPLUS> SELECT * FROM v$parameter. You must have access to the v$parameter table, which is owned by the Oracle user SYS. The Oracle SID The Oracle System Identifier (SID) identifies the Oracle instance on the machine. It is usually set up as an operating system variable— the \$ORACLE_SID environment variable in UNIX or the ORA_SID symbol in VMS—that is used to name of the Oracle background processes and to identify the SGA area in memory. Whenever a user process wants to connect to a database, the SID set up in that operating system account determines to which instance and, therefore, to which database the user will connect. The same user name can exist in different databases. For example, the Oracle system username SYS exists in all Oracle databases. With the SID, you can connect to the correct instance. Many instances might be running on the same machine, each doing the processing for a different database. By looking at the processes running on the machine, you see many occurrences of the DBWR background process. The name of the process itself usually has the SID somewhere in it. For client/server setups, the client machine identifies the network protocol and machine address to which the client machine wants to attach and the name of the SID of the connection. Requests are then processed against the database for which the instance is processing. Creating a New Database When you create a database, you create files on disk that Oracle has formatted and prepared. The structure of the database does not have to remain the same as initial structure. You can add other files later. On some platforms, you can create a new database when the Oracle software is first installed. To create a database manually after that, follow the steps in this section. It is assumed that the software has been installed correctly on your machine. The steps provided here are general steps that apply to most platforms. Creating a database involves operating system-specific steps, of course. Refer to the Oracle7 Installation and User's Guide for their platform for specific information on your platform. The crux of creating a database lies in running the CREATE DATABASE SQL statement. You must perform other steps, however, before you can run it. The syntax of the CREATE DATABASE SQL statement is CREATE DATABASE mydb LOGFILE file1, file2 SIZE nM MAXLOGFILES n MAXLOGMEMBERS n MAXLOGHISTORY n DATAFILE file1 SIZE nM MAXDATAFILES n MAXINSTANCES n ARCHIVELOG | NOARCHIVELOG Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.