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Posted to dev@hive.apache.org by "Gopal V (JIRA)" <ji...@apache.org> on 2013/03/04 23:03:13 UTC
[jira] [Created] (HIVE-4113) select count(1) reads all columns with
RCFile
Gopal V created HIVE-4113:
-----------------------------
Summary: 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
Reporter: Gopal V
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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