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1 1-1 The following is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decision. The development, release, and timing of any features or functionality described for Oracle s products remains at the sole discretion of Oracle. 1-2

2 1-3 Oracle Overview Data Operating System Oracle rdbms SQL, PL/SQL Tools Applications Client 1-4

3 Overview Memory Structures Files 1-5 The System Global Area (SGA) Shared SQL Areas Data Dictionary Cache 1-6

4 The System Global Area (SGA) 1-7 The Redo Log Buffer System Global Area (SGA) Redo Log Buffer 1-8

5 Background SMON SNPn LCKn RECO Snnn Dnnn Pnnn PMON DBWR SGA Redo Log Buffer CKPT LGWR ARCH 1-9 PMON Cleans up abnormally terminated connections. Rolls back uncommitted transactions. Releases locks held by a terminated process. Frees SGA resources allocated to the failed process. Restarts failed shared server and dispatcher processes

6 SMON Performs automatic instance recovery. Reclaims space used by temporary segments no longer in use. Merges contiguous areas of free space in the datafiles Requests SGA Stack Space PGA Session Data Request

7 Step 1: Parse SGA Shared SQL Areas SQL> SELECT first_name FROM s_emp emp; Step 2: Execute SGA Shared SQL Areas

8 Step 3: Fetch SGA Shared SQL Areas Stack Space PGA Session Data Shared SQL Areas One shared SQL area exists for identical SQL statements. SQL statements are identical when Their text strings are identical, including uppercase or lowercase, and so forth. Referenced objects are identical. The types and names of variables are identical

9 UPDATE Operation Shared SQL Areas SGA R20 Txn2 Col Addr 940 Redo Log Buffer Process 1 B2 Stock Clerk 1034 Process 2 Process 1 SQL> SQL> SELECT SELECT salary salary 2 2 FROM FROM s_emp s_emp 3 3 WHERE WHERE id id = = 17; 17; S_EMP Table Block B1 Block B2 Datafile 1 S_EMP Table Block B19 Block B20 Datafile 2 Process 2 SQL> SQL> UPDATE UPDATE s_emp s_emp 2 2 SET SET salary salary = = salary salary * * WHERE WHERE id id = = 17; 17; DBWR process System Global Area (SGA) Redo Log Buffer Shared SQL Areas DBWR Datafiles

10 Log Writer (LGWR) Process SGA DBWR LGWR Process Process Datafiles Redo Log Files Log Writer (LGWR) Process Writes redo log buffer entries to the redo log files when A commit occurs. A redo log buffer become one-third full. The DBWR completes cleaning the buffer blocks at a checkpoint. A time-out occurs. 1-20

11 An Oracle Instance Oracle Instance PMON SMON SNPn LCKn RECO Snnn Dnnn Pnnn DBWR SGA Redo Log Buffer CKPT LGWR ARCH 1-21 An Oracle Database Datafiles Control Files Redo Log Files 1-22

12 Oracle Architecture Overview SNP LCK RECO CKPT PMON SMON Shared SQL Pool System Global Area Database Buffer Cache Redo Log Buffer Request Response Shared Dedicated DBWR LGWR ARCH Dispatcher Process 1-23 Database Files Redo Log Files Multiplexed Redo Log Files Group 1 Group 2 Group 3 Disk 1 Member A Member A Member A Member B Member B Member B Disk

13 Database Checkpoints Database checkpoints ensure that all modified database buffers are written to the database files. Database files are marked current as of a given time and the checkpoint is recorded in the control file When Do Checkpoints Occur? At every log switch A specified number of seconds after the last database checkpoint When a predetermined number of redo log blocks have been written to disk since the last checkpoint At instance shut down, unless the instance is aborted When forced by a DBA When a tablespace is taken offline 1-26

14 Locking Model Readers do not block writers. Writers do not block readers. Read consistency is provided by rollback segment entries. Row-level locking is supported (default) as well as table-level level locking. Automatic as well as manual locking can be enforced. Shared or exclusive locks may be obtained manually. Row level locks are available for each row in the DB. The Oracle server never escalates locks, for example from row to page or table level Oracle Row Level Locking W R R/W W R R 1-28 Row-level locking Fine-grained resource sharing Maximizes concurrency and minimizes interference from concurrent OLTP operations No read locks!!! Non-blocking Readers never block readers, readers never block writers, writers never block readers Writers only block other writers for access to same row No lock escalation, no system-level lock limits

15 Oracle Read Consistency Query Begins Another Updates 2 Rows Consistent Read Query Continues 1-29 Multi-version read- consistency Queries see a consistent image of tables Accomodates any number of updates to a given row Automatic look-aside reads re-construct read- consistent images where necessary High-performance, low- overhead lookaside reads (rollback segment caching) Oracle Storage Architecture OS Block Part of DB Block Part of Made up of Part of Made up of Extent Used Free Part of Made up of Part of Segment Data Index Cluster Rollback Temporary Cache File Made up of Part of I n Location of Tablespace Location of Instance Part of Made up of Made up of Part of Made up of Controlling Control- led by Logical Disc Database 1-30

16 Tablespace Segment 20M Next Extent 5M Initial Extent 15M Tablespace Database Blocks File Database 1-31 Tablespaces SYSTEM tablespace Required in all databases for database operation Contains data dictionary information, definitions of stored procedures, packages and database triggers Contains the SYSTEM rollback segment Can contain user data, but should not NON-SYSTEM tablespace Allows more flexibility in database administration Consists of rollback segments, temporary segments, application data, application indexes, and user space 1-32