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https://issues.apache.org/jira/browse/ORC-744?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun resolved ORC-744.
-------------------------------
Fix Version/s: 1.7.0
Resolution: Fixed
I'm resolving this issue because all subtasks are completed.
> LazyIO of non-filter columns
> ----------------------------
>
> Key: ORC-744
> URL: https://issues.apache.org/jira/browse/ORC-744
> Project: ORC
> Issue Type: Improvement
> Components: Reader
> Affects Versions: 1.7.0
> Reporter: Pavan Lanka
> Assignee: Pavan Lanka
> Priority: Major
> Labels: releasenotes
> Fix For: 1.7.0
>
> Attachments: image-2021-01-25-14-34-45-375.png
>
>
> h2. Background
> This feature request started as a result of a large search that is performed
> with the following characteristics:
> * The search fields are not part of partition, bucket or sort fields.
> * The table is a very large table.
> * The predicates result in very few rows compared to the scan size.
> * The search columns are a significant subset of selection columns in the
> query.
> Initial analysis showed that we could have a significant benefit by lazily
> reading the non-search columns only when we have a match. We explore the
> design and some benchmarks in subsequent sections.
> h2. Design
> This builds further on ORC-577 which currently only restricts deserialization
> for some selected data types but does not improve on IO.
> On a high level the design includes the following components:
> !image-2021-01-25-14-34-45-375.png!
> * *SArg to Filter*: Converts Search Arguments passed down into filters for
> efficient application during scans.
> * *Read*: Performs the lazy read using the filters.
> ** *Read Filter Columns*: Read the filter columns from the file.
> ** *Apply Filter*: Apply the filter on the read filter columns.
> ** *Read Select Columns*: If filter selects at least a row then read the
> remaining columns.
>
> This issue has the following tasks that provides further details on the
> design of the respective components:
> # ORC-741: Bug fix related to schema evolution of missing columns in the
> presence of filters
> # ORC-742: LazyIO of non-filter columns
> # ORC-743: Conversion of SArg to Filter
>
> h2. Tests
> We evaluated this approach against a search job with the following stats:
> * Table
> ** Size: ~*420 TB*
> ** Data fields: ~*120*
> ** Partition fields: *3*
> * Scan
> ** Search fields: 3 data fields with large (~ 1000 value) IN clauses
> compounded by *OR*.
> ** Select fields: 16 data fields (includes the 3 search fields), 1 partition
> field
> ** Search:
> *** Size: ~*180 TB*
> *** Records: *3.99 T*
> ** Selected:
> *** Size: ~*100 MB*
> *** Records: *1 M*
> We have observed the following reductions compared with the absence of the
> patch:
> ||Test||IO Reduction %||CPU Reduction %||
> |Select 16 columns|45|47|
> |SELECT *|70|87|
> * The savings are more significant as you increase the number of select
> columns with respect to the search columns
> * When the filter selects most data, no significant penalty observed as a
> result of 2 IO compared with a single IO
> ** We do have a penalty as a result of the filter application on the
> selected records.
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