pgbench tests are slower on Greenplum 6.x compared to 7.x
Article ID: 427989
Updated On:
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Issue/Introduction
When running some pgbench test on Greenplum 7.x and comparing to the performance on a similar cluster running Greenplum 6.x, the test may take longer on Greenplum 7.x cluster.
An example test would be:
pgbench -i testdb --scale 10000
Cause
The cause of the difference may be resource limits set when using resource groups in Greenplum 7.x
The CPU percentage limit (CPU_MAX_PERCENT) set in resource groups in Greenplum 7.x is a hard limit. It will not allow the resource group to exceed the limit even if there is free CPU cycles available.
The CPU percentage limit (CPU_RATE_LIMIT) set in resource groups in Greenplum 6.x is NOT a hard limit and it will allow the resource group to exceed the limit.
When running these tests using the "gpadmin" user or other role with superuser authority, it will use the "admin_group" resource group. By default the "admin_group" has "CPU_MAX_PERCENT" set to 10.
Resolution
Increase the CPU_MAX_PERCENT for the resource group used by the user. Example:
ALTER RESOURCE GROUP admin_group SET CPU_MAX_PERCENT 30;
Provide the appropriate resource group name in the above example. You could also try testing with a different setting than the example above.
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