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https://issues.apache.org/jira/browse/IMPALA-8041?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul Rogers reassigned IMPALA-8041:
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Assignee: (was: Paul Rogers)
> Migrate rewrite rules to occur during expression analysis
> ---------------------------------------------------------
>
> Key: IMPALA-8041
> URL: https://issues.apache.org/jira/browse/IMPALA-8041
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Affects Versions: Impala 3.1.0
> Reporter: Paul Rogers
> Priority: Minor
>
> A number of JIRAs have been filed about issues with, or improvements to, the
> expression rewrite rules implemented in the analyzer. Work in this area
> revealed that changes in this area are quite difficult because of the way the
> code is currently structured.
> * The analyzer makes one pass over the AST to resolve references, compute
> types and so on.
> * The rewrite rules make a pass over the tree to rewrite expressions.
> * The prior analysis is discarded, and a second analysis pass is done over
> the rewritten expressions.
> Work was done to handle this two-step process. Special code exists in some
> clauses to tuck away the underwritten SQL for use in error messages after
> rewrite, though the implementation is inconsistent across clauses.
> The analyzer often makes copies of expressions for various purposes. It is
> quite hard to keep things in sync when doing rewrites as new copies must be
> made (as part of the second analysis pass.)
> The goal of this ticket is to migrate rewrites into the expression analysis
> step. For each node:
> * Analyze and rewrite children.
> * Resolve references.
> * Rewrite the node itself.
> * Compute costs and selectivity.
> Once completed, rewrites will be just another step in expression analysis.
> The analyzer will make just one analysis pass. Copies of expressions will be
> made after analysis/rewrite to that they stay in sync.
> The work will be done as a series of small patches. Those that are just
> refactoring will use this this JIRA ticket with a (Part i) designation. Those
> that make functional changes have their own JIRA tickets.
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