How to use large BLOB/CLOB in HADR

31 March,2011 by Tom Collins

Currently working on a Webspere Business Monitor application integrating with DB2 9.5 on Linux. I've made a few observations.One that is interesting , particuarly as Webspere Business Monitor uses BLOBs\CLOBs, relates to HADR and BLOB\CLOB replication.

Database logs are used in HADR , for replicating the Primary database to the Standby database.The Primary database
will support non-logged operations , such as changes to the configuration, changes to the recovery history file and BLOBs\CLOBs .But the problem - is that large BLOBs\CLOBs , which cannot be logged - cannot be replicated.

Insert, update, delete operations performed on a table with CLOBs\BLOBs that are larger that 1 GB  cannot be logged therefore  not replicated to the standby server. The space is defined on the standby server , but CLOB\BLOB is not replicated.

If a CLOB\BLOB is smaller than 1 GB and is logged , than this will be replicated

This raises questions about : 1)if large BLOBs\CLOBs need to be maintained on the Standby Server - what procedure need to be created to maintain the Standby 2)In a failover situation , would the BLOBs\CLOBS be necessary to maintain the service. Consideration needs to be given to your backup procedure, servcie levels etc  3)Is HADR the best way to maintain High Availability - there are alternatives such as Shared Disk Clustering - with Tivoli Storage Automation(TSA)

Read More on DB2 clustering

TSAMP Cheat Sheet for DBA managing DB2 clustering



Author: Rambler(


Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment on How to use large BLOB/CLOB in HADR

Comments are moderated, and will not appear until the author has approved them. | DB2 Performance Tuning | DBA DB2:Everything | FAQ | Contact | Copyright