[jira] [Commented] (IMPALA-4865) Limit size of literal values from constant folding

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    [ https://issues.apache.org/jira/browse/IMPALA-4865?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16828787#comment-16828787 ] 

ASF subversion and git services commented on IMPALA-4865:
---------------------------------------------------------

Commit 931a8f0ba7f45d5b1608e62aff397b517b943e95 in impala's branch refs/heads/master from Fang-Yu Rao
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=931a8f0 ]

IMPALA-4865: Reject Expr Rewrite When Appropriate

Avoided rewrite if the resulting string literal exceeds a defined limit.

Testing:
Added three statements in testFoldConstantsRule() to verify that the
expression rewrite is accepted only when the size of the rewritten
expression is below a specified threshold.

Change-Id: I8b078113ccc1aa49b0cea0c86dff2e02e1dd0e23
Reviewed-on: http://gerrit.cloudera.org:8080/12814
Reviewed-by: Tim Armstrong <ta...@cloudera.com>
Tested-by: Tim Armstrong <ta...@cloudera.com>


> Limit size of literal values from constant folding
> --------------------------------------------------
>
>                 Key: IMPALA-4865
>                 URL: https://issues.apache.org/jira/browse/IMPALA-4865
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Frontend
>    Affects Versions: Impala 2.8.0
>            Reporter: Henry Robinson
>            Assignee: Fang-Yu Rao
>            Priority: Major
>              Labels: newbie
>
> Consider (from {{test_insert.py}}) the following query:
> {{create table foo as select repeat('AZ', 128 * 1024 * 1024) as s}}
> {{repeat()}} gets constant-folded into a 256MB expression payload, which is then transmitted to every fragment instance that evaluates the expression. This can lead to timeouts. 
> The workaround is {{ENABLE_EXPR_REWRITES=0}}.
> It's not obvious what the answer is - should the FE be aware of the serialized size of an expression when deciding whether to constant fold it?



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