Monitoring Segment Status
The Segment Status page provides a health overview for the Greenplum Database segments and details for each primary and mirror segment.
Greenplum Database is most efficient when all segments are operating in their preferred roles. The Segment Summary panel tells you the overall segment status and if any mirrors are acting as primaries.
The Segment Summary panel provides the following information:
- Normal: The database is functioning with no major errors or performance issues.
- Segment(s) Down: The database is in change-tracking mode or resync mode. Overall performance and system reliability is greatly reduced. See the Pivotal Greenplum Database System Administrator Guide for information about resolving this condition.
- Database Unreachable: The Greenplum Performance Monitor agent cannot connect to the database. The database is likely down. See the Pivotal Greenplum Database System Administrator Guide for troubleshooting information.
- Unbalanced: Some segments are not running in their preferred roles. That is, primaries are running as mirrors and mirrors are running as primaries, resulting in unbalanced processing.
- Resyncing: The database is performing a recoverty or rebalance operation.
- Recover and Rebalance
These actions are executed from the command line using the
gprecoverseg Greenplum management utility. See
gprecoverseg in the Pivotal Greenplum Database Utility Reference for more information.
The Segment Health panel contains charts for Greenplum Database segments’ status, replication mode, and preferred roles.
Not Syncing: The primary segment and mirror segment are active and all changes to the primary segment have been copied to the mirror using a file block replication process.
Change Tracking: If a primary segment is unable to copy changes to its mirror segment using the file replication process, it logs the unsent changes locally so they can be replicated when the mirror again becomes available. This can happen if a mirror segment goes down or if a primary segment goes down and its mirror segment automatically assumes the primary role.
Resyncing: When a down segment is brought back up, administrators initiate a recovery process to return it to operation. The recovery process synchronizes the segment with the active primary and copies the changes missed while the segment was down.
Synced: Once all mirrors and their primaries are synchronized, the system state becomes synchronized.
The red portion of the Preferred Role chart shows the numbers of segments that not operating in their preferred primary or mirror roles. If the chart is not solid green, the performance of the Greenplum cluster is not optimal.
Primary and mirror segments are distributed evenly among the segment hosts to ensure that each host performs an equivalent share of the work and primary segments and their mirror segments reside on different segment hosts. When a primary segment goes down, its mirror on another host in the cluster automatically assumes the primary role, increasing the number of primary segments running on that host. This uneven distribution of the workload will affect query performance until the down segment is restored and the segments are returned to their original, preferred, roles.
The table at the bottom of the Segment Status page contains a detailed row for every primary and mirror segment in the Greenplum Cluster. The table has the following columns for each segment: