World of Oracle DBA

All about Statistics Intruduction on Statistics The CBO makes its explain-plan decisions based on statistics. Statistics provide critical input in order for CBO to work properly; these includes information such as the number of rows in a table, distinct values in a column, number of leaf blocks in an index, etc. The more accurate the statistics, the more efficient the results provided by Optimizer. Statistics may be exact or estimated: Statistics generated with a COMPUTE clause analyzes all of the data in the object. This gives the optimizer accurate information to work on and arrive at a good execution plan. Statistics generated with an ESTIMATE clause analyzes data in the object to the extent of sample size mentioned. Sample size may be specified as number of rows or percentage of rows that should be randomly analyzed to generate the statistics. Optionally block sampling may also be specified. Statistics are stored in a data dictionary tables owned by SYS user. The following views d

RAID Configuration There is significant confusion in many organizations using ORACLE and RAID technologies. I will attempt to make this information very clear and understandable. What Is RAID? RAID is the technology for expanding the capacity of the I-O system and providing the capability for data redundancy. It stands for Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks. Conceptually, RAID is the use of 2 or more physical disks, to create 1 logical disk, where the physical disks operate in tandem to provide greater size and more bandwidth. RAID has become an indispensable part of the I-O fabric of any system today and is the foundation for storage technologies, supported by many mass storage vendors. The use of RAID technology has re-defined the design methods used for building storage systems that support Oracle databases. The 3 Main Concepts In RAID When you talk about RAID, there are 3 that terms are important and relevant. • Striping • Mirro