CDR is not my favourite topic, but yes they are important and people make a lot of noise when things go wrong.  CAR can be a great tool for troubleshooting.  Some good links on this below.

CUCM CDR Overview:

https://supportforums.cisco.com/document/53056/understanding-cdr-call-detail-records

I really recommend that some is spent understand the CDR Architecture and Services for CUCM for clustered environments.

Troubleshooting CDRs:

https://supportforums.cisco.com/document/55821/troubleshooting-cdr

Managed Service Alerts – Start of CAR:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/managed_services/11_0_1/CUCM_BK_C877EEF7_00_cucm-managed-service-guide-1101/cisco_unified_serviceability_alarms_and_ciscolog_messages.html#CUCM_RF_C37FD3AB_00

CDR Administration Guide:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/service/11_0_1/cdrdef/CUCM_BK_C5ED8A7C_00_cisco-unified-cdr-analysis-and-reporting1101.html

Managed Service Alerts – Start of CDR:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/managed_services/11_0_1/CUCM_BK_C877EEF7_00_cucm-managed-service-guide-1101/cisco_unified_serviceability_alarms_and_ciscolog_messages.html#CUCM_RF_C9D0E00C_00