System Monitoring and Maintenance

Best practices for regular maintenance that will ensure Greenplum Database high availability and optimal performance.

Parent topic: Greenplum Database Best Practices

Monitoring

Greenplum Database includes utilities that are useful for monitoring the system.

The gp_toolkit schema contains several views that can be accessed using SQL commands to query system catalogs, log files, and operating environment for system status information.

The gp_stats_missing view shows tables that do not have statistics and require ANALYZE to be run.

For additional information on gpstate and gpcheckperf refer to the Greenplum Database Utility Guide. For information about the gp_toolkit schema, see the Greenplum Database Reference Guide.

gpstate

The gpstate utility program displays the status of the Greenplum system, including which segments are down, master and segment configuration information (hosts, data directories, etc.), the ports used by the system, and mapping of primary segments to their corresponding mirror segments.

Run gpstate -Q to get a list of segments that are marked "down" in the master system catalog.

To get detailed status information for the Greenplum system, run gpstate -s.

gpcheckperf

The gpcheckperf utility tests baseline hardware performance for a list of hosts. The results can help identify hardware issues. It performs the following checks:

disk I/O test – measures I/O performance by writing and reading a large file using the dd operating system command. It reports read and write rates in megabytes per second.
memory bandwidth test – measures sustainable memory bandwidth in megabytes per second using the STREAM benchmark.
network performance test – runs the gpnetbench network benchmark program (optionally netperf) to test network performance. The test is run in one of three modes: parallel pair test (-r N), serial pair test (-r n), or full-matrix test (-r M). The minimum, maximum, average, and median transfer rates are reported in megabytes per second.

To obtain valid numbers from gpcheckperf, the database system must be stopped. The numbers from gpcheckperf can be inaccurate even if the system is up and running with no query activity.

gpcheckperf requires a trusted host setup between the hosts involved in the performance test. It calls gpssh and gpscp, so these utilities must also be in your PATH. Specify the hosts to check individually (-h *host1* -h *host2* ...) or with -f *hosts_file*, where *hosts_file* is a text file containing a list of the hosts to check. If you have more than one subnet, create a separate host file for each subnet so that you can test the subnets separately.

By default, gpcheckperf runs the disk I/O test, the memory test, and a serial pair network performance test. With the disk I/O test, you must use the -d option to specify the file systems you want to test. The following command tests disk I/O and memory bandwidth on hosts listed in the subnet_1_hosts file:

$ gpcheckperf -f subnet_1_hosts -d /data1 -d /data2 -r ds

The -r option selects the tests to run: disk I/O (d), memory bandwidth (s), network parallel pair (N), network serial pair test (n), network full-matrix test (M). Only one network mode can be selected per execution. See the Greenplum Database Reference Guide for the detailed gpcheckperf reference.

Monitoring with Operating System Utilities

The following Linux/UNIX utilities can be used to assess host performance:

iostat allows you to monitor disk activity on segment hosts.
top displays a dynamic view of operating system processes.
vmstat displays memory usage statistics.

You can use gpssh to run utilities on multiple hosts.

Best Practices

Implement the "Recommended Monitoring and Maintenance Tasks" in the Greenplum Database Administrator Guide.
Run gpcheckperf at install time and periodically thereafter, saving the output to compare system performance over time.
Use all the tools at your disposal to understand how your system behaves under different loads.
Examine any unusual event to determine the cause.
Monitor query activity on the system by running explain plans periodically to ensure the queries are running optimally.
Review plans to determine whether index are being used and partition elimination is occurring as expected.

Additional Information

gpcheckperf reference in the Greenplum Database Utility Guide.
"Recommended Monitoring and Maintenance Tasks" in the Greenplum Database Administrator Guide.
Sustainable Memory Bandwidth in Current High Performance Computers. John D. McCalpin. Oct 12, 1995.
www.netperf.org to use netperf, netperf must be installed on each host you test. See gpcheckperf reference for more information.