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Background: Know: tableINDEX, OID, cell, column, row, network element , OBJECT-TYPE , SEQUENCE OF, ::=  Recognize:


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Auxiliary index objects for tablesEdit

Background information:Edit

An object identifier or OID is an identifier used to precisely name an object (compare URN) which we seek to access. Structurally, an OID consists of a node which is identified by a hierarchy context and a string or a number.The oid could be extended in both depth and width since the oid are definded universall.

Auxiliary index objects for tables:Edit

Object identification number (OID) for table:Edit

Every row in POSTGRESQLis assigned a unique, normally invisible number called an object identification number (OID).


Why we use auxiliary index object?Edit

When the software is initialized with initdb, counter is created and set to approximately seventeen-thousand. The counter is used to uniquely number every row. Although databases may be created and destroyed, the counter continues to increase. It is used by all databases, so identification numbers are always unique. No two rows in any table or in any database will ever have the same OID." OID appears only if you specifically access it. But if the value of a cell changes, references to other cells in row will be stale which means you may not be able to access these cells.To solve this problem, we use auxiliary index objects for tables. Auxiliary index objects unambiguously define each row.


Auxiliary index object:Edit

They can be used only as part of an OID, but cannot be read or written to directly. They should not be overwritten by managers because this would result in undefined behavior. As a consequence, Auxiliary index objects can avoid the unaccessible problem caused by value changing to other cells.It can direct to the object correctly.




reference
1. http://www.postgresql.org/files/documentation/books/aw_pgsql/node71.html