EC: Allow tuning ec_object_segment_size per policy

[OpenStack Infra]

https://review.openstack.org/132389
commit 4021c151adb5449e6933d3612c7aba7dca7fde7e
Author: Tushar Gohad <email address hidden>
Date: Sat Nov 1 04:49:23 2014 -0700

    EC: Allow tuning ec_object_segment_size per policy

    For 'erasure_coding' type (EC) policies, objects are buffered up to
    a defined 'segment size' before they are erasure (en)coded. There
    is a desire to make this size configurable per policy given PyECLib
    metadata/padding overheads and thus fragment sizes vary depending on
    the EC scheme and ec_num_data_fragments/ec_num_parity_fragments values
    chosen. A cluster administrator setting up an EC policy may be able
    to tune the object segment size value for a balance of space savings
    and performance for a particular EC scheme.

    Changes:

     - Parsing support for 'ec_object_segment_size' swift.conf option
     - Add 'ec_segment_size' property to ECStoragePolicy class
     - Add unit test cases for ec_object_segment_size

    Co-Authored-By: Yuan Zhou <email address hidden>

    DocImpact
    Implements: blueprint ec-proxy-work
    Change-Id: I3a9628b404e3921108c132093162331acb3e73d3

[Lana (loquacity)]

EC is still in beta in Kilo. For now, we won't be documenting specific EC tasks, only general EC concepts.

[Alexandra Settle (alexandra-settle)]

openstack-manuals at present only covers the concept information of erasure coding. There is no need to add this information into the docs. Tagging swift for dev input.

[Kota Tsuyuzaki (tsuyuzaki-kota)]

This one seems to happen in the development-cycle for erasure coding. IIRC, the capability for tuning the segment size has been ready since the first ec release so we have no task to do this anymore.