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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-806) add a column-major codec for data files
Date Wed, 20 Apr 2011 22:08:06 GMT

    [ https://issues.apache.org/jira/browse/AVRO-806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13022395#comment-13022395
] 

Doug Cutting commented on AVRO-806:
-----------------------------------

The question is not whether the elements of depth > 1 are included, but whether they're
each stored in a distinct column.  Regardless, one will read the data file in the same way,
using a schema with a subset of the fields, even if you're not using the column-major codec
at all.  So if you have a query that scans only field x.y.z, then storing values for x.y in
a column will still make things faster than a row-order, but perhaps not as fast as if x.y.z
values were stored in their own column, especially if y has a lot of other fields.  Note that
Avro's already fast at skipping string and binary values that are not desired: it reads the
length and increments the buffer pointer.  So column-major will provide the biggest speedup
for structures that have a lot of numeric fields that are often ignored queries. 

> add a column-major codec for data files
> ---------------------------------------
>
>                 Key: AVRO-806
>                 URL: https://issues.apache.org/jira/browse/AVRO-806
>             Project: Avro
>          Issue Type: New Feature
>          Components: java, spec
>            Reporter: Doug Cutting
>
> Define a codec that, when a data file's schema is a record schema, writes blocks within
the file in column-major order.  This would permit better compression and also permit efficient
skipping of fields that are not of interest.

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