Starting and stopping a standalone system¶
To quickly start and stop a Kognitio Standalone system, run one of the following commands in Linux on one of the system nodes:
Alternatively a system can be started and stopped via the
wxadmin command. Run
wxadmin, then choose the ‘server’ option followed by either ‘start’ or ‘shutdown’.
Note that Kognitio will not check for active user sessions when you stop the system, so care should be taken not to interrupt important queries. Failure to do this may temporarily affect the performance or availability of Kognitio when it is restarted, as any incomplete operations may have to be rolled back or resumed.
The rest of this article provides more detail on the various options and considerations when stopping and starting a system.
When a Kognitio system is started, there are 3 ways in which table and view images may be treated, depending on the situation:
recover old images: The system may quickly restore images that were in place before the startup, using PMA’s (see Fast Restarts below)
rebuild images: The system may rebuild all images from disk. This is much slower than recovering images, but is necessary in some situations where recovering is not possible
rebuild system table images: The system may leave user tables and views un-imaged and only rebuild system table images from disk
Recovering images will not be possible if:
one or more nodes has rebooted
there have been changes to the size and/or number of ram stores (e.g. adding new nodes, changing the RAM reserved for non-Kognitio use on nodes)
Recovering Old Images
In some situations it is possible to speed up system restarts, by reusing the memory the server was using prior to the restart, rather than having to load all objects into memory from disk. This is done via PMA areas.
PMAs (Persistent Memory Areas) contain table and view image data. They occupy a percentage of the RAM available for in-memory processing in a Kognitio system (by default 85%). The remaining RAM is used for transient data such as temporary tables created by the query optimiser, sort buffers, and so on.
To recover images (otherwise known as a ‘fast restart’), run
wxserver start on a system node. This command will attempt a fast restart, and fall back to rebuilding images if this is not possible. By default, this is equivalent to the command
wxserver start recover or image which can also be run.
To attempt a fast restart, and error if that fails, use
wxserver start recover.
To attempt a fast restart, and rebuild only system table images if that fails, use
wxserver start recover or sysimage
The percentage of RAM used for PMAs is set with the rs_core_pma_size parameter in the [boot options] section of the configuration file.
If image recovery is not desirable or possible, you can start a system without image recovery with:
``wxserver start [sysimage] without recovery``
sysimage will rebuild only system table images. If
sysimage is not specified, all images will be rebuilt.
Rebuilding System Table Images
To start a system by rebuilding only system table images, run
wxserver start sysimage.
Configuration File Options
Parameters can be set in the
[boot options] section of the config file, which control behavior when
wxserver start or
wxserver start sysimage are run:
auto_recover_on_image=[yes|no]will cause the
wxserver startcommand to attempt recovery. This defaults to ‘yes’.
auto_recover_on_sysimage=[yes|no]will case the
wxserver start sysimagecommand to attempt recovery. This defaults to ‘no’.
require_auto_recover option=[yes|no]causes all restarts to attempt recovery unless they explicitly have “without recovery” appended. This will also default to ‘no’.
Attempting to start when hardware is missing¶
The SMD prevents Kognitio starting if any essential hardware that was detected when the system was previously running is now missing. If the start fails, the SMD will try starting Kognitio again to see if the failure was caused by a transitory fault associated with an initialization, configuration or timing issue. If the failure persists then contact the Kognitio Helpdesk for further advice.