ORACLE

It is a software that is used to store the data in the rows and Columns which is referred as a Table. The Table data can be accessed by using Indexes.it is possible to have more then one index for a table.Each database should follow the CODD Rules to be called as a RDBMS(Relational Database Management System).ACID(Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. OLAP(Online Analytical Processing) is used for BW Engines for Data Analytics, Reporting and Decision Making Systems. OLTP(Online Transnational Processing) is used for ERP,CRM,SRM and SCM Engines.

Database Select Statement:

  • User Submits the Request for a Weekly Sales Report.(Display Sales Report).Display Table Records
  • The Request is received by Dispatcher and keeps it wait Queue and assign them a Freely available Dialog Work Process.
  • The Dialog Work Process will be used either for Interactive Processing or used to schedule the expensive Report in Background mode.
  • In the Interactive /background mode the Request is Interpreted by the Task handlers.
  • The Process checks if the requested content is available in R3 Buffers, if available the Response is Generated/Loaded and the response is sent to the User(maybe DDLOG will be used for checking the Time Stamp).
  • If the Response is not available in R3 BUffer then the Process is sent to the Database using DB Client and SAP Kernel
  • The SAP Work Processes are Connected to Database Work Processes @1:1 which can be displayed using Transaction ST04.
  •  The DB Process Checks whether the table exists, Field Exists, SQL Execution Plan Exists from Shared Global(SQL) Area which is part of System Global Area.(SGA is a Memory Area which is built when the database is started). if not fetch the definitions from the Physical Database.
  • The DB Process Check whether the Requested Data is available in DB Buffer Cache.it is a memory area that stores copies of data blocks read from physical data files.The response is built from DB Cache only.
  • if the Response is available in DB Cache it builds the response else DB Process fetches the data from Physical Data files and updated in DB Buffer to build the response and send to the Client Process.
  • The DB Process Handovers the Response to SAP Work Processes
  • The SAP Work Process checks whether the content is eligible for buffering, if so then keeps a copy on the application server, roll-out the User related information and the response is sent to the User.

UPDATE STATEMENT (MODIFY,DELETE,INSERT,UPDATE)

  • User Submits the Request for Updating a record or set of records, let us say a payroll, Bonus, change in pay etc..
  • The Request is received by Dispatcher and keeps it wait for Queue and assign them a Freely available Dialog Work Process.
  • The Dialog Work Process will be used either for Interactive Processing or used to schedule the massive update program in Background mode.
  • In the Interactive/Background mode, the Request is Interpreted by the Task handlers.
  • When the Dialog/Background Process Identifies the Update, then it communicates with enqueue process and obtains a lock on the record so that no other user(transaction) has update access.
  • The SAP Work Process Communicates with DB Work Process using DB Client and Kernel.
  • DB Process checks the Cache(lib,SQL,dd) and goes to the database physical data files.
  • Takes a Copy of the record to roll back into rollback/UNDO Segments
  • Locks the Record as per Database LUW and these locks are displayed in DB01.
  • The record to be updated is copied into DB Buffer for read Consistency As DB Buffers are only for Select(Read Purpose),the records are not updated in DB Buffers
  • The Records are copied into Log buffer for Update.it is a small memory area which is defined by parameter log_buffer. The redo log buffer is a circular buffer in the SGA that stores redo entries describing changes made to the database. Redo entries contain the information necessary to reconstruct or redo, changes made to the database by DML or DDL operations.
  • Log buffer is the only place where commits take place.As these Commits are in memory they are persisted (written) to disk periodically using the Process lgwr(log Writer)
  • The log writer writes to online redo logs(origlogA,origlogB,mirrlogA and mirrlogB) and DB process Updates DB Buffer.
  • The Commit information is passed to the SAP Work Process and Database writer writes to the Physical Database and the Locks are deleted and Undo Information is invalidated.

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