OpenStack Storage (Swift)
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Samuel Merritt 1880351f1a Only move too-close-together replicas when they can spread out.
Imagine a 3-zone ring, and consider a partition in that ring with
replicas placed as follows:

* replica 0 is on device A (zone 2)
* replica 1 is on device B (zone 1)
* replica 2 is on device C (zone 2)

Further, imagine that there are zero parts_wanted in all of zone 3;
that is, zone 3 is completely full. However, zones 1 and 2 each have
at least one parts_wanted on at least one device.

When the ring builder goes to gather replicas to move, it gathers
replica 0 because there are three zones available, but the replicas
are only in two of them. Then, it places replica 0 in zone 1 or 2
somewhere because those are the only zones with parts_wanted. Notice
that this does *not* do anything to spread the partition out better.

Then, on the next rebalance, replica 0 gets picked up and moved
(again) but doesn't improve its placement (again).

If your builder has min_part_hours > 0 (and it should), then replicas
1 and 2 cannot move at all. A coworker observed the bug because a
customer had such a partition, and its replica 2 was on a zero-weight
device. He thought it odd that a zero-weight device should still have
one partition on it despite the ring having been rebalanced dozens of
times.

Even if you don't have zero-weight devices, having a bunch of
partitions trade places on each rebalance isn't particularly good.

Note that this only happens with an unbalanceable ring; if the ring
*can* balance, the gathered partitions will swap places, but they will
get spread across more zones, so they won't get gathered up again on
the next rebalance.

Change-Id: I8f44f032caac25c44778a497dedf23f5cb61b6bb
Closes-Bug: 1400083
2015-01-06 10:18:23 -08:00
bin Correct misspelled words 2014-11-25 15:44:30 +00:00
doc Merge "Fix typo in apache_deployment doc" 2014-11-25 04:14:15 +00:00
etc fix example typo 2014-11-20 11:38:49 +09:00
examples Add a user variable to templates 2013-09-17 11:46:04 +10:00
swift Only move too-close-together replicas when they can spread out. 2015-01-06 10:18:23 -08:00
test Only move too-close-together replicas when they can spread out. 2015-01-06 10:18:23 -08:00
.coveragerc Align tox.ini and fix coverage jobs in jenkins. 2012-06-08 20:05:14 -04:00
.functests Move the tests from functionalnosetests 2014-01-07 15:58:11 +08:00
.gitignore fix(gitignore) : ignore *.egg and *.egg-info 2013-07-30 15:11:00 -04:00
.gitreview Add .gitreview config file for gerrit. 2011-10-24 15:05:49 -04:00
.mailmap updated AUTHORS and CHANGELOG for 2.2.0 2014-10-03 15:52:20 -07:00
.probetests Allow specify arguments to .probetests script 2013-12-24 01:18:19 -08:00
.unittests Fix coverage report for newer versions of coverage 2014-04-24 16:50:03 +00:00
AUTHORS Merge "update AUTHORS" 2014-11-21 02:30:02 +00:00
babel.cfg add pybabel setup.py commands and initial .pot 2011-01-27 00:01:24 +00:00
CHANGELOG updated AUTHORS and CHANGELOG for 2.2.0 2014-10-03 15:52:20 -07:00
CONTRIBUTING.md Workflow documentation is now in infra-manual 2014-12-05 15:30:27 +11:00
LICENSE Convert LICENSE to use unix style line endings. 2012-12-19 12:48:27 -05:00
MANIFEST.in Add requirements files to the source distribution 2013-06-03 19:26:20 +04:00
README.md added testing notes to the contributing doc 2014-12-04 10:41:11 -05:00
requirements.txt warn against sorting requirements 2014-09-03 12:03:57 -05:00
setup.cfg Fix translation setup 2014-11-19 09:11:55 -05:00
setup.py taking the global reqs that we can 2014-05-21 09:37:22 -07:00
test-requirements.txt warn against sorting requirements 2014-09-03 12:03:57 -05:00
tox.ini updated hacking rules 2014-09-25 11:04:31 -07:00

Swift

A distributed object storage system designed to scale from a single machine to thousands of servers. Swift is optimized for multi-tenancy and high concurrency. Swift is ideal for backups, web and mobile content, and any other unstructured data that can grow without bound.

Swift provides a simple, REST-based API fully documented at http://docs.openstack.org/.

Swift was originally developed as the basis for Rackspace's Cloud Files and was open-sourced in 2010 as part of the OpenStack project. It has since grown to include contributions from many companies and has spawned a thriving ecosystem of 3rd party tools. Swift's contributors are listed in the AUTHORS file.

Docs

To build documentation install sphinx (pip install sphinx), run python setup.py build_sphinx, and then browse to /doc/build/html/index.html. These docs are auto-generated after every commit and available online at http://docs.openstack.org/developer/swift/.

For Developers

The best place to get started is the "SAIO - Swift All In One". This document will walk you through setting up a development cluster of Swift in a VM. The SAIO environment is ideal for running small-scale tests against swift and trying out new features and bug fixes.

You can run unit tests with .unittests and functional tests with .functests.

If you would like to start contributing, check out these notes to help you get started.

Code Organization

  • bin/: Executable scripts that are the processes run by the deployer
  • doc/: Documentation
  • etc/: Sample config files
  • swift/: Core code
    • account/: account server
    • common/: code shared by different modules
      • middleware/: "standard", officially-supported middleware
      • ring/: code implementing Swift's ring
    • container/: container server
    • obj/: object server
    • proxy/: proxy server
  • test/: Unit and functional tests

Data Flow

Swift is a WSGI application and uses eventlet's WSGI server. After the processes are running, the entry point for new requests is the Application class in swift/proxy/server.py. From there, a controller is chosen, and the request is processed. The proxy may choose to forward the request to a back- end server. For example, the entry point for requests to the object server is the ObjectController class in swift/obj/server.py.

For Deployers

Deployer docs are also available at http://docs.openstack.org/developer/swift/. A good starting point is at http://docs.openstack.org/developer/swift/deployment_guide.html

You can run functional tests against a swift cluster with .functests. These functional tests require /etc/swift/test.conf to run. A sample config file can be found in this source tree in test/sample.conf.

For Client Apps

For client applications, official Python language bindings are provided at http://github.com/openstack/python-swiftclient.

Complete API documentation at http://docs.openstack.org/api/openstack-object-storage/1.0/content/


For more information come hang out in #openstack-swift on freenode.

Thanks,

The Swift Development Team