Hey,
I'm using Calcite to parse snippets of SQL.
My (simplified) function looks like this:
public static SqlNode expressionToNode(final String sqlExpression,
final SqlParser.Config config) {
SqlParser sqlParser = SqlParser.create(sqlExpression, config);
try {
return sqlParser.parseExpression();
} catch (SqlParseException e) {
//do something
}
}
and it is called many times.
The parser set in the config is Babel, so the parser instantiated is
SqlBabelParserImpl.
A SqlBabelParserImpl is instantiated every time this function is called.
>From what I understand this parser cannot be re-used easily to parse
different expressions but let me know if I'm incorrect.
The issue I'm encountering is the instantiation of this class is pretty
slow because one of the instance field jj_ls extends java.lang.Error and
is instantiated when the SqlBabelParserImpl is instantiated.
[image: Screenshot 2024-07-05 at 10.37.17.png]
here is the extract of the generated code in SqlBabelParserImpl:
static private final class LookaheadSuccess extends java.lang.Error { }
final private LookaheadSuccess jj_ls = new LookaheadSuccess();
final private boolean jj_scan_token(int kind) {
if (jj_scanpos == jj_lastpos) {
jj_la--;
if (jj_scanpos.next == null) {
jj_lastpos = jj_scanpos = jj_scanpos.next = token_source.getNextToken();
} else {
jj_lastpos = jj_scanpos = jj_scanpos.next;
}
} else {
jj_scanpos = jj_scanpos.next;
}
if (jj_rescan) {
int i = 0; Token tok = token;
while (tok != null && tok != jj_scanpos) { i++; tok = tok.next; }
if (tok != null) jj_add_error_token(kind, i);
}
if (jj_scanpos.kind != kind) return true;
if (jj_la == 0 && jj_scanpos == jj_lastpos) throw jj_ls;
return false;
}
jj_ls is only used in an error case. (before last line of jj_scan_token)
I'm assuming the re-use of a single error instance is done on purpose,
but could we consider instantiate jj_ls lazily?
I can try to do this but I'm a bit lost in the code generation codebase so
I would need some pointers.
Have a nice day.
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Cyril de Catheu
Software Engineer
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