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Cytat
Do celu tam się wysiada. Lec Stanisław Jerzy (pierw. de Tusch-Letz, 1909-1966)
A bogowie grają w kości i nie pytają wcale czy chcesz przyłączyć się do gry (. . . ) Bogowie kpią sobie z twojego poukładanego życia (. . . ) nie przejmują się zbytnio ani naszymi planami na przyszłość ani oczekiwaniami. Gdzieś we wszechświecie rzucają kości i przypadkiem wypada twoja kolej. I odtąd zwyciężyć lub przegrać - to tylko kwestia szczęścia. Borys Pasternak
Idąc po kurzych jajach nie podskakuj. Przysłowie szkockie
I Herkules nie poradzi przeciwko wielu.
Dialog półinteligentów równa się monologowi ćwierćinteligenta. Stanisław Jerzy Lec (pierw. de Tusch - Letz, 1909-1966)
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.The runtime area is created as the first step of an execute request.For INSERT,UPDATE, and DELETE statements, the runtime area is freed after thestatement has been executed.For queries, the runtime area is freed only afterall rows are fetched or the query is canceled.A private SQL area continues to exist until the corresponding cursor is closedor the statement handle is freed.Since Oracle frees the runtime area after thestatement completes, generally only the persistent area remains waiting.Memory Structures and Processes 5-21 Application developers should close all open cursors that will not be usedagain to minimize the amount of memory required for users of the application.For selects processing large amounts of data where sorts are needed,application developers should cancel the query if the client is satisfied with apartial result of a fetch.For example, in an Oracle Office application, a usercan select from a list of over sixty templates for creating a mail message.Oracle Office displays the first ten template names and the user chooses one ofthese templates.The application can continue to try to display more templatenames, but because the user has chosen a template, the application shouldcancel the processing of the rest of the query.The location of a private SQL area varies depending on the type of connectionestablished for a session.If a session is connected via a dedicated server,private SQL areas are located in the user s PGA.However, if a session isconnected via the multi-threaded server, the persistent areas and, for SELECTstatements, the runtime areas, are kept in the SGA.How the User Process Manages Private SQL AreasThe management of private SQL areas is the responsibility of the user process.The allocation and deallocation of private SQL areas depends largely on whichapplication tool you are using, although the number of private SQL areas thata user process can allocate is always limited by the initialization parameterOPEN_CURSORS.The default value of this parameter is 50.How Oracle Manages Shared SQL AreasSince shared SQL areas must be available to multiple users, the library cacheis contained in the shared pool within the SGA.The size of the library cache,along with the size of the data dictionary cache, is limited by the size of theshared pool.Memory allocation for shared pool is determined by theinitialization parameter SHARED_POOL_SIZE.The default value for thisparameter is 3.5 megabytes.If a user process tries to allocate a shared SQL area after the entire shared poolhas been allocated, Oracle can deallocate items from the pool using a modifiedleast-recently-used algorithm until there is enough free space for the new item.If a shared SQL area is deallocated, the associated SQL statement must bereparsed and reassigned to another shared SQL area when it is next executed.PL/SQL Program Units and the Shared PoolOracle processes PL/SQL program units (procedures, functions, packages,anonymous blocks, and database triggers) similar to processing individualSQL statements.Oracle allocates a shared area to hold the parsed, compiled5-22 Oracle8 Server Concepts form of a program unit.Oracle allocates a private area to hold values specificto the session that executes the program unit, including local, global, andpackage variables (also known as package instantiation) and buffers forexecuting SQL.If more than one user executes the same program unit, then asingle, shared area is used by all users, while each user maintains a separatecopy of his/her private SQL area, holding values specific to his/her session.Individual SQL statements contained within a PL/SQL program unit areprocessed as described in the previous sections.Despite their origins within aPL/SQL program unit, these SQL statements use a shared area to hold theirparsed representations and a private area for each session that executes thestatement.Dictionary CacheThe data dictionary is a collection of database tables and views containingreference information about the database, its structures, and its users.Amongthe data stored in the data dictionary are the following:" names of all tables and views in the database" names and datatypes of columns in database tables" privileges of all Oracle usersThis information is useful as reference material for database administrators,application designers, and end users alike.Oracle itself accesses the datadictionary frequently during the parsing of SQL statements.This access isessential to the continuing operation of Oracle.See Chapter 4, The DataDictionary for more information on the data dictionary.Since the data dictionary is accessed so often by Oracle, two special locationsin memory are designated to hold dictionary data.One area is called the datadictionary cache, also know as the row cache.The other area in memory to holddictionary data is in the library cache
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