Paul Rogers created IMPALA-8041:
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Summary: 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
Assignee: Paul Rogers
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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