From 12e4eca0e2773ccbd6eeb76665810116b4a0b881 Mon Sep 17 00:00:00 2001 From: Alex Tomic Date: Mon, 4 Jan 2016 10:52:00 -0500 Subject: [PATCH] Vertica cluster grow and shrink Spec for enabling support for growing and shrinking Vertica clusters in Trove. Change-Id: Ieae1452db52a56e0d0cd7315d7fdbec380d3ed84 --- specs/mitaka/vertica-grow-shrink-cluster.rst | 238 +++++++++++++++++++ 1 file changed, 238 insertions(+) create mode 100644 specs/mitaka/vertica-grow-shrink-cluster.rst diff --git a/specs/mitaka/vertica-grow-shrink-cluster.rst b/specs/mitaka/vertica-grow-shrink-cluster.rst new file mode 100644 index 0000000..04b62c3 --- /dev/null +++ b/specs/mitaka/vertica-grow-shrink-cluster.rst @@ -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