Urgent from Sybase: Issues that can lead to data corruption when using IQ 15.0, and later, Multiplex Grid Option utilizing multiple writers.
Summary: In the existing version of Sybase IQ 15.0 and later when using multiple writers there exist timing related issues that can lead to a bookkeeping error that ultimately leads to data integrity issues.
This document contains the following sections:
- Customer Alert
Sybase IQ 15.0 and higher can be configured in a Multiplex (MPX) configuration that contains one coordinator, multiple writers and multiple readers. This differs from previous versions that could only have a single writer and multiple readers.
The systems and root causes of the bookkeeping errors that can lead to data integrity issues are as follows:
- Race condition between Multiplex writer rollback and periodic IQ main storage maintenance can cause database integrity issues:
There is a small timing window during rollback of a global transaction on a writer where the periodic storage maintenance process will not account for the storage in use by the global transaction, causing this storage to be freed globally at the coordinator for use by other transactions and locally by the writer. This can lead to the same space being allocated by the writer and some other global transaction on another node.
- Crash recovery of the coordinator can cause database integrity issues:
There is a small timing window during the coordinator processing of periodic shared main storage maintenance where another transaction can use the space freed by the maintenance event before the event commits. This causes no problems during run time. However if the coordinator crashes or is killed after this timing window is hit and before the next checkpoint, crash recovery during the subsequent restart of the coordinator can cause book keeping errors. During recovery the transactions are recovered in the commit order and what can happen is that the space allocated to the committed transaction will be freed for use by other transactions. This can lead to the same space being allocated twice.
This alert affects versions of Sybase IQ from 15.0 up to and including 15.4 GA.
This alert also affects versions of Sybase RAP - The Trading Edition version 4.1.
Customers are advised to update to the latest EBFs for applicable versions as detailed in tables below.
The following Versions of IQ contain the fix for this issue and are available on all platforms:
- Sybase IQ 15.2 ESD #2.19
- Sybase IQ 15.2 ESD #3.10
- Sybase IQ 15.4 ESD #1
Below is a list of the impacted products:
Sybase IQ Multiplex Grid Option
||Solaris UltraSparc T, Sun Solaris UltraSPARC T, IBM AIX, Windows x64, Windows x86, Linux x86-64, HP Itanium, Linux On Power, Sun x64, Sun SPARC
||15.0, 15.1, 15.2, 15.3, 15.4
RAP – The Trading Edition & RAP – The Trading Edition Enterprise Edition
||Solaris UltraSPARC T, Sun Solaris UltraSPARC T, Sun Solaris SPARC, Linux x86-64, Sun Solaris x64, IBM AIX
Sybase is tracking this issue under CR# 683266, 681549 and 688319.
Customers using Sybase RAP - The Trading Edition should use the appropriate EBF for their platform from the list above.
EBFs are obtained from the Sybase EBFs and Maintenance site.
Follow the instructions in the EBF cover letter to install the EBF.
If you require further assistance please contact your local support center. The contact numbers can be found in the About Support section under Support & Services at the www.sybase.com website.
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