You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@hive.apache.org by "Brock Noland (JIRA)" <ji...@apache.org> on 2013/06/07 19:06:20 UTC
[jira] [Assigned] (HIVE-4113) select count(1) reads all columns
with RCFile
[ 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}
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira