Github user jbertram commented on a diff in the pull request:

    https://github.com/apache/activemq-artemis/pull/2228#discussion_r208790685
  
    --- Diff: 
artemis-selector/src/main/java/org/apache/activemq/artemis/selector/impl/SelectorParser.java
 ---
    @@ -80,11 +78,15 @@ public static BooleanExpression parse(String sql) 
throws FilterException {
                    StrictParser parser = new StrictParser(new 
StringReader(actual));
                    e = parser.JmsSelector();
                 }
    -            cache.put(sql, e);
    +            synchronized (cache) {
    --- End diff --
    
    My guess is that the LRUCache is there mainly because it was used in Apollo 
and basically the whole selector implementation from Apollo was ported over to 
the Artemis code-base during the Apache donation process.  It is a simple 
mitigation against excessive parsing, but perhaps it is premature optimization 
as well.  I don't see a big problem with pulling it out.  It would simplify the 
code-base a bit and eliminate the threading problem as well.  I certainly don't 
see any reason to invest resources into a more 
robust/elegant/higher-performance cache implementation.


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