Managing the Cluster Health Monitor Repository
(Doc ID 1921105.1)
Last updated on SEPTEMBER 16, 2021
Applies to:Oracle Database - Enterprise Edition - Version 184.108.40.206 to 220.127.116.11 [Release 11.2 to 12.2]
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Information in this document applies to any platform.
Cluster Health Monitor (CHM) collects operating system metrics that can be very useful to Oracle Support for first failure diagnostics when service requests (SRs) are filed, especially in cases where cluster node evictions might be an issue. For Oracle clusterware version 11.2 CHM collects and stores these metrics on a clusterwide basis in a highly available distributed repository. The default location of this repository is in the Grid Infrastructure Home on all RAC clusters from version 18.104.22.168 and 22.214.171.124. In 12c the CHM repository is stored in the Grid Infrastructure Management Repository in the same ASM diskgroup as the Oracle Cluster Registry (OCR) and Voting Disk. The retention time of metric data is controlled by the size of the repository and when the maximum size is reached the space is reused such that older metrics are "aged out" of the repository.
Oracle Support recommends that the CHM repository be sized according to 72 hours (three days) of data retention (e.g.., one weekend worth) so that if a Service Request is not filed within a few hours, the data needed for diagnosing the problem will still be available in the CHM repository. By default upon installation in the Grid Infrastructure home the CHM repository is not sized large enough to retain 3 days of data in most cases due to a conservative approach to space management, 2GB by default. Hence the recommendation by Oracle Support is to move the CHM repository to a filesystem where free space is not likely to become an issue for any reason and to resize the CHM repository large enough so as to maintain 3 days of OS performance metrics.
CHM samples and stores the OS performance metrics every five seconds. For space estimating and planning purposes in version 11.2, 3 days of data retention for each node in a cluster will require approximately 2.6GB of disk space in the CHM repository. So the number of nodes in a cluster can be multiplied by 2.6GB to arrive at the amount of space that would be required.
This information is intended for DBAs and System Administrators. Care should be taken to understand and verify free space before re-sizing the CHM repository as is discussed in this note.
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