Monthly Archives: dicembre 2013

Automatic Undo Management (AUM) ORACLE 9i
  • 23
    Dic

Automatic Undo Management (AUM) ORACLE 9i

In Oracle 8i and below, Rollback Segments provide read consistency and the ability to rollback transactions. In Oracle 9i, Undo segments can be used to provide this functionality. The advantage of using Automatic Undo Management is that it relieves the DBA of manually creating, sizing and monitoring the rollback segments in the database. To start using Automatic Undo...

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Useful query to find out Oracle Licensing Option usage
  • 18
    Dic

Useful query to find out Oracle Licensing Option usage

  Below SQL statement is useful to comply Oracle licensing. It also as a useful tools to check whether specific option has been used before it can be safely removed/deinstalled. SQL> desc DBA_FEATURE_USAGE_STATISTICS Name Null? Type ----------------------------------------- -------- ----------------- DBID NOT NULL NUMBER NAME NOT NULL VARCHAR2(64) VERSION NOT NULL VARCHAR2(17) DETECTED_USAGES NOT NULL NUMBER TOTAL_SAMPLES NOT NULL...

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Index Tuning
  • 11
    Dic

Index Tuning

Oracle indexes can be tuned looking to three main characteristics: SELECTIVITY: you can calculate index selectivity using this formula: SELECT DISTINCT_KEYS/NUM_ROWS SELECTIVITY FROM DBA_INDEXES / Values range from 0 to 1, where 1 is the optimal value (UNIQUE indexes and PK), while with values near to 0 performance is lower CLUSTERING FACTOR: measures how many keys are stored...

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Create an Index By Table of Record
  • 9
    Dic

Create an Index By Table of Record

An index by table is an associative array. An associative array never has more than two columns: the variable being indexes and the index value. However you can combine a record with an associative array to tie multiple values to the same index.   In this case the array still has a variable and an index, but the...

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