GitHub user xuchuanyin opened a pull request:
https://github.com/apache/carbondata/pull/1253
[CARBONDATA-1373] Enhance update performance by increasing parallelism
# Scenario
Recently I have tested the update feature provided in Carbondata and found
its poor performance.
I had a table containing about 14 million records with about 370 columns(no
dictionary columns) and the data files are about 3.8 GB in total. All the data
files were in one segment.
I performed an update SQL which update a column for all the records and the
SQL looked like `UPDATE myTable SET (col1)=(col1+1000) WHERE TRUE`. In my
environment, the update job failed with 'executor lost errors'. And I found
'spill data' related messages in the container logs.
# Analyze
I've read about the implementation of update-delete in Carbondata in
ISSUE#440. The update consists a delete and an insert operation. And the error
occurred during the insert operation.
After studying the code, I have found that while doing inserting, the
updated records are grouped by the `segmentId`, which means all the recoreds in
one segment will be processed in only one task, thus will cause task failure
when the amount of input data is quite large.
# Solution
We should improve the parallelism when doing update for a segment.
I append a random key to the `segmentId` to increase the partition number
before doing the insertion stage and then remove the suffix when doing the real
insertion.
# Modification
+ Increase parallelism while processing one segment in update
+ Add a property to configure the parallelism
+ Clean up local files after update (previous bugs)
# Notes
I have tested in my example and the job finished in about 13 minutes
successfully. The records were updated as expected.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/xuchuanyin/carbondata enhance_update
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/carbondata/pull/1253.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1253
----
commit 84a4fe5e9afcd127cf976cda55bc6bfd8faf4e32
Author: xuchuanyin <[email protected]>
Date: 2017-08-11T15:00:20Z
Enhance update performance by increasing parallelism
+ Increase parallelism while processing one segment in update
+ Add a property to configure the parallelism
+ Clean up local files after update (previous bugs)
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