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https://issues.apache.org/jira/browse/CALCITE-6585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17882484#comment-17882484
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Norman Jordan commented on CALCITE-6585:
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A first step here is to split the operations of compiling a DateTime format
string and applying that format to a DateTime value. A compiled format string
would be a sequence of individual format patterns and literal strings. For
example "YYYY-MM-DD" would end up with the following sequence:
# Pattern for YYYY
# Literal string "-"
# Pattern for MM
# Literal string "-"
# Pattern for DD
This sequence is analogous to a compiled RegEx pattern and could be cached.
> In the Postgres TO_CHAR function, improve caching
> -------------------------------------------------
>
> Key: CALCITE-6585
> URL: https://issues.apache.org/jira/browse/CALCITE-6585
> Project: Calcite
> Issue Type: Improvement
> Reporter: Julian Hyde
> Assignee: Norman Jordan
> Priority: Major
>
> In the Postgres TO_CHAR function (and similar functions added in
> CALCITE-6358), cache the formatter using the same technique used in
> CALCITE-5914.
> Also pass the {{DataContext}} into the constructor of {{class
> DataFormatFunction}}, so that it does not need to be passed to each call to
> {{toCharPg}}.
> In {{DateFormatFunction}} obsolete static field {{LOCAL_ZONE}} and instead
> populate a non-static field {{zoneId}} from the {{DataContext}} constructor
> parameter.
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