Merge "Vertica cluster grow and shrink"
This commit is contained in:
Jenkins
Gerrit Code Review
commit
34ad2d86b9
238
specs/mitaka/vertica-grow-shrink-cluster.rst
Normal file
238
specs/mitaka/vertica-grow-shrink-cluster.rst
Normal file
@ -0,0 +1,238 @@
|
||||
..
|
||||
This work is licensed under a Creative Commons Attribution 3.0 Unported
|
||||
License.
|
||||
|
||||
http://creativecommons.org/licenses/by/3.0/legalcode
|
||||
|
||||
Sections of this template were taken directly from the Nova spec
|
||||
template at:
|
||||
https://github.com/openstack/nova-specs/blob/master/specs/juno-template.rst
|
||||
|
||||
..
|
||||
This template should be in ReSTructured text. The filename in the git
|
||||
repository should match the launchpad URL, for example a URL of
|
||||
https://blueprints.launchpad.net/trove/+spec/awesome-thing should be named
|
||||
awesome-thing.rst.
|
||||
|
||||
Please do not delete any of the sections in this template. If you have
|
||||
nothing to say for a whole section, just write: None
|
||||
|
||||
Note: This comment may be removed if desired, however the license
|
||||
notice above should remain.
|
||||
|
||||
|
||||
=======================================
|
||||
Vertica Cluster Grow and Shrink Support
|
||||
=======================================
|
||||
|
||||
.. If section numbers are desired, unindent this
|
||||
.. sectnum::
|
||||
|
||||
.. If a TOC is desired, unindent this
|
||||
.. contents::
|
||||
|
||||
The Vertica database has elastic grow/shrink capabilities which are not
|
||||
currently supported by the Vertica guest agent for Trove.
|
||||
|
||||
Launchpad Blueprint:
|
||||
https://blueprints.launchpad.net/trove/+spec/vertica-grow-shrink-cluster
|
||||
|
||||
|
||||
Problem Description
|
||||
===================
|
||||
|
||||
The Vertica guest agent currently does not leverage the underlying elastic
|
||||
capabilities of Vertica. This will enable a user to grow a cluster in the
|
||||
event that they wish to accommodate more data or enable faster query
|
||||
performance, while scaling down helps avoid costs associated with
|
||||
overprovisioning.
|
||||
|
||||
Proposed Change
|
||||
===============
|
||||
|
||||
As Vertica was architected from the ground up to be a clustered system, adding
|
||||
and removing nodes is relatively simple in comparison to other datastores.
|
||||
|
||||
Configuration
|
||||
-------------
|
||||
|
||||
A minimum k-safety configuration option will be added for vertica to allow
|
||||
the operator to decide their desired level of fault tolerance.
|
||||
|
||||
|
||||
Database
|
||||
--------
|
||||
|
||||
None
|
||||
|
||||
|
||||
Public API
|
||||
----------
|
||||
|
||||
The following public API calls will be made available to the Vertica datastore.
|
||||
|
||||
* Cluster Grow - The existing call payload will not be changed. Implementing
|
||||
the grow cluster feature will add the new instances to the existing cluster.
|
||||
* Cluster Shrink - The existing call payload will not be changed.
|
||||
Implementing the shrink cluster feature will allow a user to remove
|
||||
instances from their existing cluster.
|
||||
|
||||
Public API Security
|
||||
-------------------
|
||||
|
||||
None
|
||||
|
||||
|
||||
Python API
|
||||
----------
|
||||
|
||||
None
|
||||
|
||||
|
||||
CLI (python-troveclient)
|
||||
------------------------
|
||||
|
||||
Support for the following existing CLI calls.
|
||||
|
||||
* cluster-grow
|
||||
* cluster-shrink
|
||||
|
||||
No changes should be nessesary to accomplish these actions.
|
||||
|
||||
|
||||
Internal API
|
||||
------------
|
||||
|
||||
None.
|
||||
|
||||
Guest Agent
|
||||
-----------
|
||||
|
||||
To enable more efficient grow and shrink, local data segmentation will be
|
||||
enabled on Vertica [1]_. This creates additional local, logical segments of
|
||||
data on a node to enable easier shipping of data between nodes. The number of
|
||||
local segments is configurable with the scaling factor variable. Local
|
||||
segmentation has the drawback of making tables with many hundreds of
|
||||
projections less efficient [2]_.
|
||||
|
||||
Grow
|
||||
~~~~
|
||||
|
||||
Growing a cluster involves two main steps [3]_.
|
||||
|
||||
First, a new "host" must be added to the cluster, which in the case of trove
|
||||
would mean a new instance. The update_vertica script is then called, similar
|
||||
to the install_vertica script, which handles installation of the vertica
|
||||
binaries.
|
||||
|
||||
Second, the host must be added as a node to the database. The adminTools
|
||||
utility is called with the db_add_node command to register the host with the
|
||||
database.
|
||||
|
||||
Shrink
|
||||
~~~~~~
|
||||
|
||||
Removing a node from a Vertica cluster proceeds inversely to addition, with
|
||||
an extra check to ensure that the minimum k-safety level of the system is
|
||||
maintained.
|
||||
|
||||
If a user attempts to remove a node that would lower the k-safety
|
||||
level below the configured level, an error will be thrown.
|
||||
|
||||
After the k-safety check, the host is removed from the database [4]_.
|
||||
Similarly as with grow, the adminTools utility will be called using the
|
||||
db_remove_node command.
|
||||
|
||||
Then, the host to be removed is removed from the cluster, using the same
|
||||
update_vertica script but with the --remove-hosts option.
|
||||
|
||||
K-safety
|
||||
~~~~~~~~
|
||||
|
||||
Vertica defines three K-safety levels for the number of nodes K that could
|
||||
fail while allowing the cluster to continue to operate: K=0 for clusters
|
||||
with 1 or 2 nodes, K=1 for clusters with 3 or 4 nodes, and K=2 for 5 or
|
||||
more [5]_ [6]_.
|
||||
|
||||
Rather than prevent a user from removing nodes that would result in a lower
|
||||
k-safety value, it is up to the operator to define a minimum level of safety
|
||||
she is willing to accept. For example, in some cases it may be that the costs
|
||||
associated with overprovisioning the cluster outweigh the risk of data being
|
||||
unavailable.
|
||||
|
||||
Alternatives
|
||||
------------
|
||||
|
||||
Trove could enforce a minimum k-safety level to ensure the integrity of the
|
||||
cluster, but this could be too restrictive.
|
||||
|
||||
|
||||
Implementation
|
||||
==============
|
||||
|
||||
Assignee(s)
|
||||
-----------
|
||||
|
||||
atomic77
|
||||
|
||||
|
||||
Milestones
|
||||
----------
|
||||
|
||||
Mitaka-3
|
||||
|
||||
|
||||
Work Items
|
||||
----------
|
||||
|
||||
- Grow cluster
|
||||
- Shrink cluster
|
||||
|
||||
|
||||
Upgrade Implications
|
||||
====================
|
||||
|
||||
None.
|
||||
|
||||
Dependencies
|
||||
============
|
||||
|
||||
None
|
||||
|
||||
Testing
|
||||
=======
|
||||
|
||||
Integration tests will be added or modified as needed in order to test
|
||||
grow/shrink with the new int-test framework.
|
||||
|
||||
Documentation Impact
|
||||
====================
|
||||
|
||||
The documentation should be updated to reflect the fact that grow and shrink is
|
||||
supported for Vertica clusters.
|
||||
|
||||
Dashboard Impact (UX)
|
||||
=====================
|
||||
|
||||
There will be some minor changes to the UI to support grow and shrink buttons
|
||||
for the cluster.
|
||||
|
||||
References
|
||||
==========
|
||||
|
||||
.. [1] https://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/AdministratorsGuide/ClusterManagement/ElasticCluster/LocalDataSegmentation.htm
|
||||
.. [2] The Vertica documentation recommends local data segmentation be done
|
||||
with numbers of nodes that are a power of two. Some experimentation
|
||||
will be required to see what is whether violating this recommendation
|
||||
is still worthwhile compared to not using local data segmentation at
|
||||
all
|
||||
|
||||
.. [3] https://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/AdministratorsGuide/ManageNodes/AddingNodes.htm
|
||||
.. [4] https://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/AdministratorsGuide/ManageNodes/RemovingNodes.htm
|
||||
.. [5] https://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/AdministratorsGuide/ManageNodes/LoweringTheK-SafetyLevelToAllowForNodeRemoval.htm
|
||||
.. [6] https://my.vertica.com/docs/7.1.x/HTML/Content/Authoring/ConceptsGuide/Components/HighAvailabilityAndRecovery.htm
|
||||
|
||||
Appendix
|
||||
========
|
||||
|
||||
None
|
||||
Loading…
Reference in New Issue
Block a user