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Key: DERBY-96
Type: Improvement Improvement
Status: Closed Closed
Resolution: Fixed
Priority: Major Major
Assignee: Suresh Thalamati
Reporter: Suresh Thalamati
Votes: 0
Watchers: 0
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Derby

partial log record writes that occur because of out-of order writes need to be handled by recovery.

Created: 09/Dec/04 08:11 PM   Updated: 01/Jul/09 12:34 AM
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Component/s: Store
Affects Version/s: 10.0.2.1
Fix Version/s: 10.1.1.0

Time Tracking:
Not Specified

Resolution Date: 28/May/05 09:07 AM


 Description  « Hide
Incomplete log record write that occurs because of
an out of order partial writes gets recognized as complete during
recovery if the first sector and last sector happens to get written.
 Current system recognizes incompletely written log records by checking
the length of the record that is stored in the beginning and end.
 Format the log records are written to disk is:

  +----------+-------------+------------------+

  | length | LOG RECORD | length |

  +----------+-------------+------------------+


This mechanism works fine if sectors are written in sequential manner or
log record size is less than 2 sectors. I believe on SCSI types disks
order is not necessarily sequential, SCSI disk drives may sometimes do a
reordering of the sectors to optimize the performance. If a log record
that spans multiple disk sectors is being written to SCISI type of
devices, it is possible that first and last sector written before the
crash; If this occurs recovery system will incorrectly interpret the
log records was completely written and replay the record. This could
lead to recovery errors or data corruption.
-


This problem also will not occur if a disk drive has write cache with a
battery backup which will make sure I/O request will complete.

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Suresh Thalamati made changes - 13/Dec/04 06:42 PM
Field Original Value New Value
Assignee Suresh Thalamati [ tsuresh ]
Suresh Thalamati made changes - 28/May/05 09:07 AM
Fix Version/s 10.1.0.0 [ 10993 ]
Status Open [ 1 ] Resolved [ 5 ]
Resolution Fixed [ 1 ]
Suresh Thalamati made changes - 07/Jun/05 08:55 AM
Status Resolved [ 5 ] Closed [ 6 ]
Dag H. Wanvik made changes - 01/Jul/09 12:34 AM
Issue Type New Feature [ 2 ] Improvement [ 4 ]