23 Nov

Conquering your database workloads using WLM

Conquering Your Database Workloads

Howard Goldberg – Executive Director,  Morgan Stanley,  Head of Greenplum engineering

1  Introduction

Everyone has been in some type of traffic delay, usually at the worst possible time. These traffic jams result from an unexpected accident, volume on the roadway, or lane closures forcing a merge from multiple lanes into a single lane. These congestion events lead to unpredictable travel times and frustrated motorists.

Databases also have traffic jams or periods when database activity outpaces the resources (CPU/Disk IO/Network) supporting it. These database logjams cause a cascade of events leading to poor response times and unhappy clients. To manage a database’s workload, Greenplum (4.3+) utilizes resource queues and the Greenplum Workload Manager (1.8+). Together these capabilities control the use of the critical database resources and allow databases to operate at maximum efficiency. This article will describe these workload manager capabilities and offer best practices where applicable. Read More

11 Nov

Altered States: Greenplum Alter Table Command by Howard Goldberg

A common question that is frequently asked when performing maintenance on Greenplum tables is “Why does my ALTER TABLE add column DDL statement take so long to run?” Although it appears to be a simple command and the expectations are that it will execute in minutes this is not true depending on the table organization (heap, AO columnar compressed, AO row compressed), number of range partitions and the options used in the alter table command.

Depending on the size of the table a rewrite table operation triggered by an alter table/column DDL command could take from minutes to multiple hours. During this time the table will hold the access exclusive locks and may cause cascading effects on other ETL processing. While this rewrite operation is occurring there is no easy way to predict its completion time. Please note that since Greenplum supports polymorphic tables a range partitioned table can contain all three table organizations within a single parent table, this implies that some child partitions can trigger a rewrite while others may be altered quickly. However, all operations on a range partitioned table must complete before the DDL operation is completed.

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14 Sep

Pivotal Greenplum: Life in a Vacuum by Howard Goldberg

Vacuuming your home is a laborious task that you would rather not do.  However, vacuuming your home is an essential chore that must be done. The same is true for vacuuming the catalog in a Pivotal Greenplum database (“Greenplum”). The proper maintenance and care is required for the Greenplum catalog to keep the database functioning at its peak efficiency. Read More