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Greenplum is based on MPP (massively parallel processing) architecture. It built on shared nothing mode parallel processing in which all child segments own separate resources.
Database Theory: What is Parallel Query Processing (Parallel Database System)?
When you are taking database backup in Greenplum, it executes a backup process in different stages and executes in parallel.
For GP DBA, this is very important for knowing that in which machine or segment backup process is running. They may have few other questions like Is backup process completed for a master segment?, If it is completed for a master segment, in which child segment it is running currently.
You can access this article for troubleshooting Greenplum running database backup process.
You can start Greenplum full database backup using below command:
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gpcrondump -x database_name -u /home/gpadmin/dbrnd_backup/ |
It first takes a backup of the master node (all metadata or pg_catalog), while during this time you cannot perform any DDL or any other operation on Greenplum database server like CREATE TABLE, DROP TABLE, TRUNCATE TABLE.
It takes only a few minutes to complete the backup of a master node.
How can you check that, Is Greenplum database backup process running on master node?
The first step is to check if the message “Starting Dump process” is on the screen
After this message, you can find a subsequent message “Releasing pg_class lock” that means backup process completed for master segment (meta data backup).
You can measure the time difference between “Starting Dump process” and “Releasing pg_class lock” that is the total time taken for master segment backup.
If you are unable to find “Releasing pg_class lock” on the screen and find only “Starting Dump process” for a long time, there is 99% problem with a master segment and problem like database lock, network issue, disk failure.
How can we check that, Is Greenplum database backup process running on child nodes?
After taken a master node back up, a gp_dump command will be sent to all the segments to start a copy of the data using COPY command.
We can check the running processes in child nodes and can find COPY command and db_dumps directory in the process list. You can get the list of Linux running processes using a command: ps -ef.
Below is a sample process message:
Important Note:
Please do not kill long running Greenplum backup from only master node because it may continue the backup process on child segments. Your one wrong kill command can fail your whole Greenplum cluster.
If you guys know how to kill long running backup in Greenplum, please share full detail with me because I am also looking for the solution for killing backup process at all child segments.
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