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Posted to issues-all@impala.apache.org by "ASF subversion and git services (Jira)" <ji...@apache.org> on 2023/05/28 01:49:00 UTC
[jira] [Commented] (IMPALA-8125) Limit number of files generated by insert
[ https://issues.apache.org/jira/browse/IMPALA-8125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17726874#comment-17726874 ]
ASF subversion and git services commented on IMPALA-8125:
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Commit dbddb0844713677cd5165c55fe21ef46238d3e24 in impala's branch refs/heads/master from Riza Suminto
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=dbddb0844 ]
IMPALA-12120: Limit output writer parallelism based on write volume
The new processing cost-based planner changes (IMPALA-11604,
IMPALA-12091) will impact output writer parallelism for insert queries,
with the potential for more small files if the processing cost-based
planning results in too many writer fragments. It can further exacerbate
a problem introduced by MT_DOP (see IMPALA-8125).
The MAX_FS_WRITERS query option can help mitigate this. But even without
the MAX_FS_WRITERS set, the default output writer parallelism should
avoid creating excessive writer parallelism for partitioned and
unpartitioned inserts.
This patch implements such a limit when using the cost-based planner. It
limits the number of writer fragments such that each writer fragment
writes at least 256MB of rows. This patch also allows CTAS (a kind of
DDL query) to be eligible for auto-scaling.
This patch also remove comments about NUM_SCANNER_THREADS added by
IMPALA-12029, since it does not applies anymore after IMPALA-12091.
Testing:
- Add test cases in test_query_cpu_count_divisor_default
- Add test_processing_cost_writer_limit in test_insert.py
- Pass test_insert.py::TestInsertHdfsWriterLimit
- Pass test_executor_groups.py
Change-Id: I289c6ffcd6d7b225179cc9fb2f926390325a27e0
Reviewed-on: http://gerrit.cloudera.org:8080/19880
Reviewed-by: Impala Public Jenkins <im...@cloudera.com>
Tested-by: Impala Public Jenkins <im...@cloudera.com>
> Limit number of files generated by insert
> -----------------------------------------
>
> Key: IMPALA-8125
> URL: https://issues.apache.org/jira/browse/IMPALA-8125
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Reporter: Tim Armstrong
> Assignee: Bikramjeet Vig
> Priority: Major
> Labels: multithreading
> Fix For: Impala 4.0.0
>
>
> One pitfall of multithreaded execution is that, if implemented naively, the number of files generated by an unpartitioned insert will be multiplied by mt_dop.
> We should provide a mechanism to limit the number of files generated, e.g. limit the number of insert fragment instances (note that there a pre-existing problem with unpartitioned inserts generating too many files).
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