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From "Daniel Vimont (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17257) Add column-aliasing capability to hbase-client
Date Mon, 12 Dec 2016 09:44:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15741486#comment-15741486

Daniel Vimont commented on HBASE-17257:

In doing my own code review of my own stuff, I am noting the following:

Given the way things are currently coded, read/write access to an alias-enabled Table (i.e.
a table with one or more alias-enabled column families) requires that the Master server be
accessible (due to the need to invoke #getTableDescriptor method). I'm pretty sure that things
could be altered to remove this requirement, but the current constraint is that Master server
must be accessible.

I have already received one person's assurance (off-line) that there is no need to assure
access to a table when Master server is down, but in a lot of the standard write-ups about
HBase, it is touted that basic read-write access to tables can continue even when the Master
is down. So I wanted to get consensus on whether or not alias-enabled tables need to remain
accessible (for read/write access) when the Master server is inaccessible.

> Add column-aliasing capability to hbase-client
> ----------------------------------------------
>                 Key: HBASE-17257
>                 URL: https://issues.apache.org/jira/browse/HBASE-17257
>             Project: HBase
>          Issue Type: New Feature
>          Components: Client
>    Affects Versions: 2.0.0
>            Reporter: Daniel Vimont
>            Assignee: Daniel Vimont
>              Labels: features
>         Attachments: HBASE-17257-v2.patch, HBASE-17257-v3.patch, HBASE-17257.patch
> Review Board link: https://reviews.apache.org/r/54635/
> Column aliasing will provide the option for a 1, 2, or 4 byte alias value to be stored
in each cell of an "alias enabled" column-family, in place of the full-length column-qualifier.
Aliasing is intended to operate completely invisibly to the end-user developer, with absolutely
no "awareness" of aliasing required to be coded into a front-end application. No new public
hbase-client interfaces are to be introduced, and only a few new public methods should need
to be added to existing interfaces, primarily to allow an administrator to designate that
a new column-family is to be alias-enabled by setting its aliasSize attribute to 1, 2, or
> To facilitate such functionality, new subclasses of HTable, BufferedMutatorImpl, and
HTableMultiplexer are to be provided. The overriding methods of these new subclasses will
invoke methods of the new AliasManager class to facilitate qualifier-to-alias conversions
(for user-submitted Gets, Scans, and Mutations) and alias-to-qualifier conversions (for Results
returned from HBase) for any Table that has one or more alias-enabled column families. All
conversion logic will be encapsulated in the new AliasManager class, and all qualifier-to-alias
mappings will be persisted in a new aliasMappingTable in a new, reserved namespace.
> An informal polling of HBase users at HBaseCon East and at the Strata/Hadoop-World conference
in Sept. 2016 showed that Column Aliasing could be a popular enhancement to standard HBase
functionality, due to the fact that full column-qualifiers are stored in each cell, and reducing
this qualifier storage requirement down to 1, 2, or 4 bytes per cell could prove beneficial
in terms of reduced storage and bandwidth needs. Aliasing is intended chiefly for column-families
which are of the "narrow and tall" variety (i.e., that are designed to use relatively few
distinct column-qualifiers throughout a large number of rows, throughout the lifespan of the
column-family). A column-family that is set up with an alias-size of 1 byte can contain up
to 255 unique column-qualifiers; a 2 byte alias-size allows for up to 65,535 unique column-qualifiers;
and a 4 byte alias-size allows for up to 4,294,967,295 unique column-qualifiers.
> Fuller specifications will be entered into the comments section below. Note that it may
well not be viable to add aliasing support in the new "async" classes that appear to be currently
under development.

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