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From "Brock Noland (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (HIVE-4113) select count(1) reads all columns with RCFile
Date Fri, 07 Jun 2013 17:06:20 GMT

     [ https://issues.apache.org/jira/browse/HIVE-4113?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Brock Noland reassigned HIVE-4113:
----------------------------------

    Assignee: Brock Noland
    
> select count(1) reads all columns with RCFile
> ---------------------------------------------
>
>                 Key: HIVE-4113
>                 URL: https://issues.apache.org/jira/browse/HIVE-4113
>             Project: Hive
>          Issue Type: Bug
>          Components: File Formats
>            Reporter: Gopal V
>            Assignee: Brock Noland
>
> select count(1) loads up every column & every row when used with RCFile.
> "select count(1) from store_sales_10_rc" gives
> {code}
> Job 0: Map: 5  Reduce: 1   Cumulative CPU: 31.73 sec   HDFS Read: 234914410 HDFS Write:
8 SUCCESS
> {code}
> Where as, "select count(ss_sold_date_sk) from store_sales_10_rc;" reads far less
> {code}
> Job 0: Map: 5  Reduce: 1   Cumulative CPU: 29.75 sec   HDFS Read: 28145994 HDFS Write:
8 SUCCESS
> {code}
> Which is 11% of the data size read by the COUNT(1).
> This was tracked down to the following code in RCFile.java
> {code}
>       } else {
>         // TODO: if no column name is specified e.g, in select count(1) from tt;
>         // skip all columns, this should be distinguished from the case:
>         // select * from tt;
>         for (int i = 0; i < skippedColIDs.length; i++) {
>           skippedColIDs[i] = false;
>         }
> {code}

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