Significance of Data Source Histories table (cmdb_datasource_last_update)

[RahulY00040]

Hello team,

I have been troubleshooting some update issues with Reconciliation against multiple data sources. Then i came across this table-  cmdb_datasource_last_update which is referenced in Reconciliation process. This is also mentioned in this article:https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0756709

In my case, higher precedence data source is not able to update the value and record is missing in this table. I am not sure what's preventing it from being updated.

What if records get deleted from this table, then how is it handled by ServiceNow IRE?

Thanks,
Rahul

[pavani_paluri]

Hi @RahulY00040 ,

What is cmdb_datasource_last_update?
Think of it as IRE’s memory log — it remembers:

Which data source last updated a CI

When it happened

IRE uses this to decide:

“Should I replace the existing value or keep it?”

What happens if a record is missing?
If an entry for that CI and source isn’t there, IRE thinks:

“This source has never updated this CI before.”

It will then compare the incoming update to what’s in the CMDB and follow your precedence rules.

Why might a higher-precedence source fail to update?
Even if your source is “higher precedence”:

Another source may have updated the field more recently, so IRE keeps that value.

Your incoming data might have an older timestamp than what’s already stored.

Field-level precedence rules may not be set correctly.

What if records get deleted?
If you delete from this table:

IRE forgets who last updated that CI from that source.

Next time that source sends data, IRE treats it like a first-time update.

The table entry gets re-created when the update succeeds.

In short:

This table = IRE’s update history.

Missing = IRE doesn’t know if you’ve updated before.

Deleted = IRE forgets and will rebuild when you send new updates.

Mark it helpful if this helps you to understand. Accept solution if this give you the answer you're looking for

Kind Regards,

Pavani P

[RahulY00040]

Thanks for your quick response @pavani_paluri . But in my instance, still I am not able to understand why SN is not updating the fields if there is no entry in Data Source Histories table. I will keep you updated what I find.

Thanks again,

Rahul