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https://issues.apache.org/jira/browse/IMPALA-4192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16568546#comment-16568546
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Michael Ho commented on IMPALA-4192:
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Some initial steps were done in this patch:
https://github.com/apache/impala/commit/b38d9826d7ef9bc0ecff548626d30690f935e9c3
> Pull all expressions in a fragment into RuntimeState
> ----------------------------------------------------
>
> Key: IMPALA-4192
> URL: https://issues.apache.org/jira/browse/IMPALA-4192
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 2.8.0
> Reporter: Michael Ho
> Assignee: Michael Ho
> Priority: Major
> Labels: codegen
>
> Currently, Exprs in a fragment are scattered through the TPlanNode in a
> fragment. Expr is supposed to be shared by all threads but they are always
> accessed through thread-private state ExprContext. With multi-threading, an
> Expr in a fragment and its generated IR function should be shared among all
> instances of it.
> As part of IMPALA-4080, all Expr in a fragment will be moved to query-wide
> state instead of having multiple copies of them in the exec nodes of each
> instances. In addition, moving Expr to query-wide state prevents the mistakes
> of baking in thread private states (e.g. ExprContext pointers) into the
> generated IR code for an Expr.
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