For those who have either upgraded or fresh-installed 12.1 (12c) Grid Infrastructure stack, will notice a new database instance (-MGMTDB) that was provisioned automagically. So what is this MGMTDB and why do I need this overhead.
Si let’s recap what the DB is and what it does…
Management Database is the central repository to store Cluster Health Monitor, the Grid Infrastructure Management Repository.
MGMT database is a container database (CDB) with one pluggable database (PDB) running. However, this database runs out of the Grid Infrastructure home.
The MGMTDB is a Rac One Node database; i.e., it runs on one node at a time, but because this is Clustered Resource, it can be started or failed over on any node in the cluster. MGMTDB is as a non-critical component of the GI stack (with no “real” hard dependencies). This means that if MGMTDB fails or becomes unavailable, Grid Infrastructure continues running
MGMTDB is configured (subject to change) with 750 MB SGA/325 MB PGA, and 5GB database size. But note that, due to the footprint MGMT’s SGA is not configured for hugepages . Since, this database is dynamically created on install, the OUI installer does not have pre-knowledge of the database that are configured or will be migrated to this cluster, thus in order to avoid any database names conflict the name “-MGMTDB” was chosen (notice the “-“). Note, bypassing MGMTDB installation is only allowed for upgrades to 18.104.22.168. New 22.214.171.124 installations or upgrades to future releases will require MGMTDB to be installed. if MGMTDB is not selected during upgrade, all features (Cluster Health Monitor (CHM/OS) etc) that depend on it will be disabled.
So if you are wondering where the datafiles and other structures are stored for this database. Well they would will be stored in the same diskgroup as OCR and VOTE However, these dtabase files can be migrated into ASM diskgroup post install.
MGMTDB will store a subset of Operating System (OS) performance data for longer term to provide diagnostic information and support intelligent workload management. Performance data (OS metrics similar to, but a subset of Exawatcher) collected by the ‘Cluster Health Monitor’ (CHM) is stored also on local disk, so when not using MGMTDB, CHM data can still be obtained from local disk but intelligent workload management (QoS) will be disabled. onger term MGMTDB will become a key component of the Grid Infrastructure and provide services for important components, because of this MGMTDB will eventually become a mandatory component in future upgrades to releases on Exadata.
See document 1568402.1 for more details.