Troubleshooting Enabling Resource Groups

If you experience problems enabling resource groups in Greenplum Command Center, review the following list to ensure prerequisites are met and all of the dependencies are properly configured.

Red Hat 6.x and 7.x and CentOS 6.x and 7.x are currently supported.
You must be running Greenplum Database version 5.7.0 or later.
Configure the Linux cgroups kernel feature on your hosts by following the instructions at “Prerequisite” in Using Resource Groups.
Make sure the /etc/cgconfig.d/gpdb.conf file contains the objects perm, cpu, and cpuacct. If the document is incorrect and the gp_resource_manager configuration parameter is set to "group", Greenplum Database can hang at startup.
```
group gpdb {
  perm {
    task {
      uid = gpadmin;
      gid = gpadmin;
    }
    admin {
      uid = gpadmin;
      gid = gpadmin;
    }
  }
  cpu {
  }
  cpuacct {
  }
}
```
On Red Hat 7, make sure you run cgconfigparser -L /etc/cgconfig.d to parse changes to the /etc/cgconfig.d/gpdb.conf file. This command must also be set up to run at boot time.

Set the Greenplum Database gp_resource_manager server configuration parameter to "group" and restart Greenplum Database.

$ gpconfig -c gp_resource_manager -v "group"
$ gpstop -ar

Verify by showing the value of the parameter:

$ gpconfig -s gp_resource_manager
Values on all segments are consistent
GUC          : gp_resource_manager
Master  value: group
Segment value: group

After installing a Pivotal Greenplum Database distribution, the shared_preload_libraries configuration parameter contains the metrics collector shared library. Make sure this library is still present:
```
$ gpconfig -s shared_preload_libraries
Values on all segments are consistent
GUC          : shared_preload_libraries
Master  value: metrics_collector
Segment value: metrics_collector
```
Check that the shared library exists at $GPHOME/lib/postgresql/metrics_collector.so. If the library does not exist, make sure you have installed the Pivotal Greenplum Database distribution. This extension is not available in the Greenplum Database Open Source version.

If the shared library file exists in the $GPHOME/lib/postgresql directory, but not in the shared_preload_libraries parameter, add it with the gpconfig command:
```
$ gpconfig -c shared_preload_libraries -v 'metrics_collector'
```
Note that adding metrics_collector to the shared_preload_libraries parameter does not enable the metrics_collector or gp_wlm extensions, but is a prerequisite for enabling them.
The gpmon user must be able to connect to databases from the Command Center host. Make sure to add a host entry like the following in the $MASTER_DATA_DIRECTORY/pg_hba.conf file.
```
host   all   gpmon   <IP_of_host>/32   md5
```

Check whether the gp_wlm extension is installed. The extension is added when you click Enable Workloads in the Greenplum Command Center Admin> Workload Mgmt view.

$ psql gpperfmon
\dx  
gpperfmon=# \dx
                          List of installed  extensions
       Name        | Version |   Schema   |              Description
-------------------+---------+------------+---------------------------------------
 gp_wlm            | 0.1     | gpmetrics  | Greenplum Workload Manager Extension
 metrics_collector | 1.0     | gpmetrics  | Greenplum Metrics Collector Extension
 plpgsql           | 1.0     | pg_catalog | PL/pgSQL procedural language
(3 rows)

Make sure the gpmetrics.workload_config table and functions are present in the gpperfmon database:

gpperfmon=# \d gpmetrics.workload_config
Table "gpmetrics.workload_config"
  Column  |  Type   | Modifiers
----------+---------+-----------
 dist_col | integer |
 config   | json    |
Distributed by: (dist_col)    

gpperfmon=# \df gpmetrics.*
                                       List of functions
  Schema   |              Name              | Result data type | Argument data types  |  Type
-----------+--------------------------------+------------------+----------------------+--------
 gpmetrics | get_workload_config            | json             |                      | normal
 gpmetrics | metrics_collector_start_worker | void             |                      | normal
 gpmetrics | set_workload_config            | boolean          | wlm_json_config json | normal
(3 rows)

If the gpmetrics.workload_config table or the functions are not present, dropping and recreating the gp_wlm extension will create them. Note that any assignment rules saved in the gpmetrics.workload_config table will have to be recreated in Command Center.

$ psql gpperfmon
gpperfmon=# DROP EXTENSION gp_wlm;
DROP EXTENSION
gpperfmon=# CREATE EXTENSION gp_wlm;
CREATE EXTENSION