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https://issues.apache.org/jira/browse/CALCITE-3753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17021415#comment-17021415
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Julian Hyde commented on CALCITE-3753:
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You have to have some kind of a queue. Because a rule call might fire several
rules, each of which might fire several rules. I think that firing depth-first
(i.e. using a stack) would have some bad consequences, so we should at least
use a FIFO queue (i.e. breadth-first).
Can you precisely define "substitution rule"? Give some examples of what is and
is not a substitution rule.
> Always try to match and execute substitution rule first and remove rulematch
> ordering
> -------------------------------------------------------------------------------------
>
> Key: CALCITE-3753
> URL: https://issues.apache.org/jira/browse/CALCITE-3753
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Haisheng Yuan
> Priority: Major
>
> In VolcanoPlanner, some rules e.g. ProjectMergeRule, PruneEmptyRule can be
> defined as SubstitutionRule, so that we can always try to match and execute
> them first (without deferring rule call). All the other rulematches doesn't
> need to be sorted and rules can be executed in any order they matched, since
> we are going to execute all of them anyway, sooner or later. Computing and
> comparing importances cause a lot of latency.
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