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https://issues.apache.org/jira/browse/HIVE-4104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13591008#comment-13591008
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Gopal V commented on HIVE-4104:
-------------------------------
Before
{code}
2013-03-01 05:15:13 Dump the hashtable into file:
file:/tmp/root/hive_2013-03-01_17-14-59_468_442960319525994949/-local-10002/HashTable-Stage-1/MapJoin-customer_demographics-01--.hashtable
2013-03-01 05:15:27 Upload 1 File to:
file:/tmp/root/hive_2013-03-01_17-14-59_468_442960319525994949/-local-10002/HashTable-Stage-1/MapJoin-customer_demographics-01--.hashtable
File size: 18426794
2013-03-01 05:15:27 End of local task; Time Taken: 22.314 sec.
{code}
After
{code}
2013-03-01 05:15:53 Dump the hashtable into file:
file:/tmp/root/hive_2013-03-01_17-15-39_668_1531738824783900468/-local-10002/HashTable-Stage-1/MapJoin-demographics-01--.hashtable
2013-03-01 05:15:54 Upload 1 File to:
file:/tmp/root/hive_2013-03-01_17-15-39_668_1531738824783900468/-local-10002/HashTable-Stage-1/MapJoin-demographics-01--.hashtable
File size: 18426794
2013-03-01 05:15:54 End of local task; Time Taken: 9.601 sec.
{code}
Savings are found on the map-side read as well.
Before
{code}
Job 0: Map: 4 Cumulative CPU: 64.79 sec HDFS Read: 300156 HDFS Write: 1682
SUCCESS
Total MapReduce CPU Time Spent: 1 minutes 4 seconds 790 msec
Time taken: 56.385 seconds, Fetched: 100 row(s)
{code}
After
{code}
Job 0: Map: 4 Cumulative CPU: 26.95 sec HDFS Read: 300156 HDFS Write: 1682
SUCCESS
Total MapReduce CPU Time Spent: 26 seconds 950 msec
Time taken: 38.173 seconds, Fetched: 100 row(s)
{code}
> Hive localtask does not buffer disk-writes or reads
> ---------------------------------------------------
>
> Key: HIVE-4104
> URL: https://issues.apache.org/jira/browse/HIVE-4104
> Project: Hive
> Issue Type: Bug
> Reporter: Gopal V
> Assignee: Gopal V
> Priority: Minor
>
> Hive's HashMapWrapper does not use any buffering in its File I/O, but
> operates sequentially for writes & reads.
> The strace logs show clearly that
> {code}
> 9495 write(222, "x", 1) = 1
> 9495 write(222, "sq\0~\0\5", 6) = 6
> 9495 write(222, "w\25", 2) = 2
> 9495 write(222, "\0\0\0\1\0\0\0\1\0\0\0\2\0\0\0\5\3\1M\1S", 21) = 21
> 9495 write(222, "x", 1) = 1
> 9495 write(222, "sq\0~\0\2", 6) = 6
> 9495 write(222, "w\t", 2) = 2
> 9495 write(222, "\0\0\0\5\1\215\r\325v", 9) = 9
> {code}
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