Questions on Backup and Recovery

1. Questions on Backup and Recovery • What is the value of cold backup? • What's the difference between startup and startup mount? When we do "alter database open“, what does it mean? • What's the archive log function? • When I did 'alter database open', I still get an error. But once I issued 'recover database' and then 'alter database open‘, everything works just fine. What happens between these steps? ITEC 450

2. Module 4 Database Tuning ITEC 450 Section 5 Optimization of Physical Design

3. Techniques for Optimizing Database • Partitioning – breaking a single large table into sections (partitions) stored in multiple files • Raw versus file systems – OS-controlled file or not • Clustering – enforcing the physical sequence of data on disk • Free space and compression – storage management • File placement and allocation • Page size (block size in Oracle) – using the proper page size for efficient data storage and I/O ITEC 450

4. Partitioning • Partitioning supports very large tables and indexes by decomposing them into smaller and more manageable pieces called partitions. • SQL queries and DML statements do not need to be modified in order to access partitioned tables • After partitions are defined, DDL statement can access and manipulate individual partitions if they choose to, rather than entire tables or indexes ITEC 450

5. Raw Device vs. File System • Raw device is a UNIX feature to bypass operating system cache mechanism. • File system is a common way to manage storage. • Raw device might provide a slight performance benefit, but the database storage management is a nightmare. • Unless it is required by DBMS features, you should avoid to implementing Raw Device. ITEC 450

6. Clustering Clustering is used to store one or more tables physically together with the share common columns and are often used together. • Because related rows are physically stored together, disk access time improves. • Clustering usually is enforced by the DBMS with a cluster index. • Like indexes, clusters do not affect application design. Data stored in a clustered table is accessed by SQL in the same way as data stored in a non-clustered table. ITEC 450

7. Clustering Example ITEC 450

8. Free Space and Compression • Free space – pre-allocate storage of tablespace, tables and indexes to store newly added data • In DDL statements, a parameter is PCTFREE • Benefits and disadvantages are listed in the textbook • Compression – shrink the size of a database • Tables or indexes can be algorithmically compressed. • The DMBS will handle the reading and writing automatically. ITEC 450

9. File Placement and Allocation A database is very I/O intensive, the location of the files can be critical to database performance and recovery. • Separate the indexes from the data – traditional approach • Analyze the access patterns of your applications and separate the files for tables/indexes that are frequently accessed together • Place transaction logs on a separate disk device from the actual data, and spread out log members (redo01.log, redo02.log, redo03.log) to different physical disk devices • Place control files (control01.ctl, control02.ctl, control03.ctl) like transaction logs to different physical disk devices. It’s common to have control01.ctl shares the same device with redo01.log, etc. • Place archive logs on a complete separate disk device from any database files ITEC 450

10. Block Size The block or page size is the smallest unit of I/O, and used to store data records. • The size selection is depending on record lengths – small block size is good for small record length; large block size is good for long record length • Typical page size are 2K, 4K, 8K, 16K, and 32K. • Common used sizes are 2K and 4K • Data Warehouse or Data Mart applications use 8K, 16K or 32K. • Oracle allows to specify block size on tablespace level – tablespace for small row-size tables uses 2K, tablespace for large row-size tables uses 8K. ITEC 450

11. Module 4 Database Tuning ITEC 450 Section 6 Storage Management

12. Space Management As a DBA, you should track the following: • Objects approaching an “out of space” condition • Free space available – physical and logical perspective • Segment or partition size – understand large or small tables • Number of extents – less than hundreds • Fragment usage information – performance concern • Amount of reserved space that is currently unused – any waste situation ITEC 450

13. Data Page Layouts Three basic components exist in a data page (block in Oracle term) • Page header – general page information, such as a page identifier, an identifier indicating to which table the page belongs, free space pointers • Offset table – pointers to each data row on the data page • Data rows – actual rows of user data (table or index) • Row header – general row information, such as row length, information on variable-length data • Offset tables – pointers to manage and control for variable-length fields • Row data – actual data for the row ITEC 450

14. RAID Technology (Week 6) RAID is an acronym for Redundant Arrays of Inexpensive Disks. Please refer http://www.acnc.com/04_01_00.html • RAID-0 – data striping: striped disk array without fault tolerance. • RAID-1 – data mirroring: all data is written to two or more drives. • RAID-5 – data stripping with distributed parity blocks, and it requires a minimum of 3 drives to implement (commonly 5 drives) • RAID-10 – mirrored data stripping: very high reliability with high performance. ITEC 450

15. Modern Storage Technology • Storage Area Networks (SAN) – interconnected network of storage devices (dedicate connections between host and storage) • Shared storage between multiple hosts • High I/O performance • Server and storage consolidation • Used for database files, I/O intensive/high performance • Network-Attached Storage (NAS) – storage that can be accessed directly from the network • Shared storage between multiple hosts • Simpler management due to reducing duplicate storage • Application based storage access at file level • Good for shared folders, program files ITEC 450

16. Module 4 Database Tuning ITEC 450 Section 7 Data Movement and Distribution in Oracle

17. The LOAD Utility Oracle has SQL*Loader utility to perform bulk inserts of data into database tables. • You can transform data before loading • You can selectively load from the input file based on conditions • You can load all or part of a table • You can perform simultaneous data loads • Two main steps to use SQL*Loader • Prepare the data file – contains data in certain formats, field terminators • Create a control file – defines how to map the data fields to a table and specifies if the data needs to be transformed ITEC 450

18. Data Pump Export and Import Oracle offers the Data Pump technology for fast data movement between Oracle databases. • Migrating databases from development to test or production • Copying data between dev/test and production databases • Transferring data between Oracle databases on different operating system platforms • Backing up important tables or databases • Reorganizing fragmented table data • Extracting the DDL for tables and other objects ITEC 450

19. Data Pump Export Examples • Create a directory in Operating System for the dump directory C:\app\Administrator\admin\orcl450\dpdir1 • Within Oracle, define and verify the directory for Data Pump SQL> create directory dpdir1 as ‘C:\app\Administrator\admin\orcl450\dpdir1’; SQL> select * from dba_directories where directory_name like 'DP%'; • Export a table from command line (Run-> cmd) C:\> expdp system/password TABLES=hr.employees DIRECTORY=dpdir1 dumpfile=output01.dmp • Export a schema C:\> expdp system/password SCHEMAS=hr DIRECTORY=dpdir1 dumpfile=output02.dmp • You can also export a tablespace or full database ITEC 450

20. Data Pump Import Examples You can import the information from the dump file generated from Export. • Import to extract the DDL from the export dump file C:\> impdp system/password DIRECTORY=dpdir1 dumpfile=output01.dmp SQLFILE=emp01.sql • Import a table to another schema C:\> impdp system/password DIRECTORY=dpdir1 dumpfile=output01.dmp REMAP_SCHEMA=hr:scott • You can also import a schema, tablespace or full database ITEC 450

21. Database Refreshing Options • Backup and restore • Backup the source database, and restore to the target location • Commonly used for full database refresh • Bath databases have similar physical structures • Data pump • Export the source database/schema/table, and then import to the target database • Can be used for full, schema, or table level database refresh • SQL*Loader • Dump the source database tables to files in certain format, and then use SQL*Loader to upload the table data • Often used for table refresh, different DMBS, or user ad-hoc files ITEC 450

22. Lock Conflicts • A share lock partially locks data where there is still partial access allowed to data by other sessions • An exclusive lock completely prohibits changes to data, but still allows read access • Locking of transactions and tables (using transactional control commands or LOCK TABLE) create locking situations manually ITEC 450

23. How to Detect Lock Conflicts ITEC 450

24. How to Detect Lock Conflicts ITEC 450

25. How to Detect Lock Conflicts ITEC 450

26. What is a Deadlock? • Deadlock: one thing is waiting for another, but that other thing is also waiting for something • A pending lock request cannot be serviced, because the lock required will never be released • Can cause serious performance issues • Most common cause is manual locking of data using LOCK TABLE or the FOR UPDATE clause • Usually deadlocked sessions must be rolled back manually • Ways of resolving a deadlock manually are: • Rollback one of the deadlocked transactions • Kill one of the sessions executing one of the deadlocked transactions ITEC 450