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From "Paul Rogers (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DRILL-5235) Nested select doubles sort data size when reading a text file
Date Sun, 19 Feb 2017 22:47:44 GMT

     [ https://issues.apache.org/jira/browse/DRILL-5235?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Paul Rogers updated DRILL-5235:
-------------------------------
    Summary: Nested select doubles sort data size when reading a text file  (was: Column or
table alias doubles sort data size when reading a text file)

> Nested select doubles sort data size when reading a text file
> -------------------------------------------------------------
>
>                 Key: DRILL-5235
>                 URL: https://issues.apache.org/jira/browse/DRILL-5235
>             Project: Apache Drill
>          Issue Type: Improvement
>    Affects Versions: 1.9.0
>            Reporter: Paul Rogers
>            Priority: Minor
>
> Consider a simple query that reads data from a pipe-separated-value file and sorts it.
The file has just one column. The query looks something like this:
> {code}
> SELECT columns[0] col1 FROM `dfs.data`.`input-file.tbl` ORDER BY col1
> {code}
> Looking at the query plan, we see that a project operator not just creates an alias {{col1}}
for {{column\[0]}}, it also makes a *copy*.
> The particular input file is 20 GB in size and contains just one column. As a result
of materializing the alias, data size to the sort doubles to 40 GB. This results in doubling
query run time. If the sort must spill to disk, run times increases by a much larger factor.
> The fix is to treat the alias as an alias, not a materialized copy.
> {code}
> {
>   "graph" : [ {
>     "pop" : "fs-scan",
>     "columns" : [ "`columns`[0]" ],
>   }, {
>     "pop" : "project",
>     "@id" : 4,
>     "exprs" : [ {
>       "ref" : "`col1`",
>       "expr" : "`columns`[0]"
>     } ],
>   }, {
>     "pop" : "external-sort",
>     "orderings" : [ {
>       "order" : "ASC",
>       "expr" : "`col1`",
>       "nullDirection" : "UNSPECIFIED"
>     } ],
>   }, {
>     "pop" : "selection-vector-remover",
>   }, {
>     "pop" : "project",
>   }, {
>     "pop" : "screen",
>   } ]
> }
> {code}



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