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https://issues.apache.org/jira/browse/HADOOP-9530?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julien Serdaru updated HADOOP-9530:
-----------------------------------
Description:
The DBInputFormat on Oracle does not create valid ranges.
The method getSplit line 263 is as follows:
split = new DBInputSplit(i * chunkSize, (i * chunkSize) + chunkSize);
So the first split will have a start value of 0 (0*chunkSize).
However, the OracleDBRecordReader, line 84 is as follows:
if (split.getLength() > 0 && split.getStart() > 0){
Since the start value of the first range is equal to 0, we will skip the block
that partitions the input set. As a result, one of the map task will process
the entire data set, rather than the partition.
I'm assuming the fix is trivial and would involve removing the second check in
the if block.
Also, I believe the OracleDBRecordReader paging query is incorrect.
Line 92 should read:
query.append(" ) WHERE dbif_rno > ").append(split.getStart());
instead of (note > instead of >=)
query.append(" ) WHERE dbif_rno >= ").append(split.getStart());
Otherwise some rows will be ignored and some counted more than once.
A map/reduce job that counts the number of rows based on a predicate will
highlight the incorrect behavior.
was:
The DBInputFormat on Oracle does not create valid ranges.
The method getSplit line 263 is as follows:
split = new DBInputSplit(i * chunkSize, (i * chunkSize)
+ chunkSize);
So the first split will have a start value of 0 (0*chunkSize).
However, the OracleDBRecordReader, line 84 is as follows:
if (split.getLength() > 0 && split.getStart() > 0){
Since the start value of the first range is equal to 0, we will skip the block
that partitions the input set. As a result, one of the map task will process
the entire data set, rather than the partition.
I'm assuming the fix is trivial and would involve removing the second check in
the if block.
Also, I believe the OracleDBRecordReader paging query is incorrect.
Line 92 should read:
query.append(" ) WHERE dbif_rno > ").append(split.getStart());
instead of (note > instead of >=)
query.append(" ) WHERE dbif_rno >= ").append(split.getStart());
Otherwise some rows will be ignored and some counted more than once.
A map/reduce job that counts the number of rows based on a predicate will
highlight the incorrect behavior.
> DBInputSplit creates invalid ranges on Oracle
> ---------------------------------------------
>
> Key: HADOOP-9530
> URL: https://issues.apache.org/jira/browse/HADOOP-9530
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 1.1.2
> Reporter: Julien Serdaru
>
> The DBInputFormat on Oracle does not create valid ranges.
> The method getSplit line 263 is as follows:
> split = new DBInputSplit(i * chunkSize, (i * chunkSize) +
> chunkSize);
> So the first split will have a start value of 0 (0*chunkSize).
> However, the OracleDBRecordReader, line 84 is as follows:
> if (split.getLength() > 0 && split.getStart() > 0){
> Since the start value of the first range is equal to 0, we will skip the
> block that partitions the input set. As a result, one of the map task will
> process the entire data set, rather than the partition.
> I'm assuming the fix is trivial and would involve removing the second check
> in the if block.
> Also, I believe the OracleDBRecordReader paging query is incorrect.
> Line 92 should read:
> query.append(" ) WHERE dbif_rno > ").append(split.getStart());
> instead of (note > instead of >=)
> query.append(" ) WHERE dbif_rno >= ").append(split.getStart());
> Otherwise some rows will be ignored and some counted more than once.
> A map/reduce job that counts the number of rows based on a predicate will
> highlight the incorrect behavior.
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