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https://issues.apache.org/jira/browse/HIVE-22929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17047308#comment-17047308
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Zoltan Haindrich commented on HIVE-22929:
-----------------------------------------
[~kkasa] do we need the power of regexp to address the original issue? I think
it was something like:
{code}
str.replaceAll("``","`")
{code}
I think a special tailored utility function would probably perform even
better...could you see how this performs:
{code}
public String fx(String s, char c) {
StringBuilder sb = new StringBuilder();
char[] cc = s.toCharArray();
char l = 0;
for (int i = 0; i < cc.length; i++) {
char curr = cc[i];
if (l == '`') {
l = 0;
continue;
} else {
l = curr;
}
sb.append(curr);
}
return sb.toString();
}
{code}
note: for performance measurements you can write tests under the
itests/hive-jmh ; there are a few there already.
...I think another approach could be: since we have a lexer here (somewhere)
...we might be able to convince it to process these escapings/etc for us - not
sure at what cost it could do that...
I would recommend to not change this all over the place - it might not affect
general performance; for example the performance gain at places like a ddltask
is irrelevant...I think it's best to focus on the performance issue at hand -
the impact of the same issue is usually neglegible at other places
[~gopalv] Could you please provide a sample query for this? it might be
interesting to take a look at it - in case it heats up something like a
"String.replaceAll" function
> Performance: quoted identifier parsing uses throwaway Regex via
> String.replaceAll()
> -----------------------------------------------------------------------------------
>
> Key: HIVE-22929
> URL: https://issues.apache.org/jira/browse/HIVE-22929
> Project: Hive
> Issue Type: Bug
> Reporter: Gopal Vijayaraghavan
> Assignee: Krisztian Kasa
> Priority: Major
> Attachments: HIVE-22929.1.patch, String.replaceAll.png
>
>
> !String.replaceAll.png!
> https://github.com/apache/hive/blob/master/parser/src/java/org/apache/hadoop/hive/ql/parse/HiveLexer.g#L530
> {code}
> '`' ( '``' | ~('`') )* '`' { setText(getText().substring(1,
> getText().length() -1 ).replaceAll("``", "`")); }
> {code}
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