Browse Prior Art Database

Non-Logging Method to Reduce Risk of Overflowing Database Log during Rollback

IP.com Disclosure Number: IPCOM000112430D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Bezviner, DE: AUTHOR [+2]

Abstract

Index B+ tree restructuring operations may occur during database transac- tion rollbacks. For example, when undoing a Delete Key operation and there is no space left in the node to reinsert the key, index nodes at one or more levels must be split to make room for the key. Since node splits are unpredictable, it is not practical to always reserve enough log space to guarantee that the required log space for Undo processing will be available for index restructuring.

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This is the abbreviated version, containing approximately 64% of the total text.

Non-Logging Method to Reduce Risk of Overflowing Database Log during
Rollback

      Index B+ tree restructuring operations may occur during
database transac- tion rollbacks.  For example, when undoing a Delete
Key operation and there is no space left in the node to reinsert the
key, index nodes at one or more levels must be split to make room for
the key.  Since node splits are unpredictable, it is not practical to
always reserve enough log space to guarantee that the required log
space for Undo processing will be available for index restructuring.

      To eliminate log space usage for index restructuring occurring
during Undo processing, an "Index Consistency Flag" can be added to
the root node of the index.  This flag will have one of two values:

o   Consistent:  Indicates that the index structure is consistent.

o   Inconsistent:  Indicates an inconsistent index structure.

      Instead of logging index restructuring operations occurring
during rollback, the Index Consistency Flag is set to "Inconsistent"
and the root node's page is forced to disk.  When the restructuring
operation is complete, the affected pages are forced to disk.  The
Index Consistency Flag is then reset back to "Consistent".  The root
page should then be forced to disk, but it is not absolutely
necessary.

      Assuming restructuring operations are serialized, no
transaction should ever encounter an inconsistent index unless a
system failure occurred while an index rest...