Starting and Stopping HAWQ
In a HAWQ DBMS, the database server instances (the master and all segments) are started or stopped across all of the hosts in the system in such a way that they can work together as a unified DBMS.
Because a HAWQ system is distributed across many machines, the process for starting and stopping a HAWQ system is different than the process for starting and stopping a regular PostgreSQL DBMS.
object commands to start and stop HAWQ, respectively. These management tools are located in the $GPHOME/bin directory on your HAWQ master host. Initializing a HAWQ system also starts it.
Do not issue a
KILL command to end any Postgres process. Instead, use the database command
Initialize and start the HAWQ system using configuration parameters defined in
hawq init command with the appropriate cluster or node command initializes and starts a HAWQ cluster. The master or segment nodes can be individually initialized by using
hawq init master and
hawq init segment commands, respectively. Format options can also be specified at this time.
hawq init <object> utility will create a HAWQ instance using configuration parameters defined in
$GPHOME/etc/hawq-site.xml A single node cluster can be started without any user-defined changes to the default
hawq-site.xml file. Use the template-hawq-site.xml file to specify the configuration for larger clusters.
When using the template for initializing a new cluster configuration, replace the items contained within the % markers, for example in:
%master.host% would be replaced with the master host name. After modification, rename the file to the name of the default configuration file:
- Before initializing HAWQ, set the
$GPHOMEenvironment variable to point to the location of your HAWQ installation on the master host and exchange SSH keys between all host addresses in the array, using
To initialize and start a HAWQ cluster, enter the following command on the master host:
$ hawq init cluster
Start an initialized HAWQ system by running the
hawq start command on the master instance.
hawq start cluster command to start a HAWQ system that has already been initialized by the
hawq init cluster command, but has been stopped by the
hawq stop cluster command. The
hawq start cluster command starts HAWQ by starting all the segments on the HAWQ cluster.
hawq start cluster orchestrates this process and performs the process in parallel.
You can also use the
hawq start master command to start only the HAWQ master, without segment nodes, then add these later, using
hawq start segment. If you want HAWQ to ignore hosts that fail ssh validation, use the hawq start
hawq start clusteron the master host to start a HAWQ system:
$ hawq start cluster
When the HAWQ system is first initialized with the
hawq initcommand, it is automatically started.
Stop the HAWQ system and then restart it.
hawq restart command with the appropriate cluster or node command can stop and then restart HAWQ after the shutdown completes. If the master or segments are already stopped, restart will have no effect.
To restart a HAWQ cluster, enter the following command on the master host:
$ hawq restart cluster
Reload changes to the HAWQ configuration files without interrupting the system.
hawq stop command can reload changes to the pg_hba.conf configuration file and to runtime parameters in the hawq-site.xml file and pg_hba.conf file without service interruption. Active sessions pick up changes when they reconnect to the database. Many server configuration parameters require a full system restart (
hawq restart cluster) to activate. For information about server configuration parameters, see the Server Configuration Parameter Reference.
Reload configuration file changes without shutting down the system using the
$ hawq stop --reload
Start only the master to perform maintenance or administrative tasks without affecting data on the segments.
Maintenance mode is a superuser-only mode that should only be used when required for a particular maintenance task. For example, you can connect to a database only on the master instance in maintenance mode and edit system catalog settings.
hawq startusing the master -m option:
$ hawq start master -m
Connect to the master in maintenance mode to do catalog maintenance. For example:
$ PGOPTIONS='-c gp_session_role=utility' psql template1
After completing your administrative tasks, restart the master in production mode.
$ hawq restart master
Incorrect use of maintenance mode connections can result in an inconsistent system state. Only expert users should perform this operation.
hawq stop cluster command stops or restarts your HAWQ system and always runs on the master host. When activated,
hawq stop cluster stops all
postgres processes in the system, including the master and all segment instances. The
hawq stop cluster command uses a default of up to 64 parallel worker threads to bring down the segments that make up the HAWQ cluster. The system waits for any active transactions to finish before shutting down. To stop HAWQ immediately, use fast mode. The commands
hawq stop master,
hawq stop segment,
hawq stop standby, or
hawq stop allsegments can be used to stop the master, the local segment node, standby, or all segments in the cluster. Stopping the master will stop only the master segment, and will not shut down a cluster.
To stop HAWQ:
$ hawq stop cluster
To stop HAWQ in fast mode:
$ hawq stop cluster -M fast
For best results in using
hawq start and
hawq stop to manage your HAWQ system, the following best practices are recommended.
CHECKPOINTcommand to update and flush all data files to disk and update the log file before stopping the cluster. A checkpoint ensures that, in the event of a crash, files can be restored from the checkpoint snapshot.
Stop the entire HAWQ system by stopping the cluster on the master host.
$ hawq stop cluster
To stop segments and kill any running queries without causing data loss or inconsistency issues, use
immediatemode on the cluster:
$ hawq stop cluster -M fast $ hawq stop cluster -M immediate
hawq stop masterto stop the master only. If you cannot stop the master due to running transactions, try using fast shutdown. If fast shutdown does not work, use immediate shutdown. Use immediate shutdown with caution, as it will result in a crash-recovery run when the system is restarted.
$ hawq stop master -M fast $ hawq stop master -M immediate
When stopping a segment or all segments, you can use the default mode of smart mode. Using fast or immediate mode on segments will have no effect since segments are stateless.
$ hawq stop segment $ hawq stop allsegments
Typically you should always use
hawq start clusteror
hawq restart clusterto start the cluster. If you do end up using
hawq start standby|master|segmentto start nodes individually, make sure you always start the standby before the active master. Otherwise, the standby can become unsynchronized with the active master.