On a 1000 sample regex queries extracted from hive:
Avg clauses per regex: 52
13 regexes generate more than 1024 clauses : stat1002:/home/dcausse/insource/more_than_1024.txt

Code:

    @Test
    public void testInsource() throws IllegalArgumentException, TooComplexToDeterminizeException, IOException {
        Pattern pat = Pattern.compile("insource:/(.*?[^\\\\])/");
        int above1024 = 0;
        int sum = 0;
        int total = 0;
        Map<String, Integer> regexes = new HashMap<>();
        try(BufferedReader br = new BufferedReader(new InputStreamReader(this.getClass().getResourceAsStream("/insource_queries.txt")))) {
            String line = null;
            while((line = br.readLine()) != null) {
                Matcher m = pat.matcher(line);
                while(m.find()) {
                    String reg = m.group(1);
                    int maxExpand = 4;
                    int maxStatesTraced = 10000;
                    int maxDeterminizedStates = 20000;
                    int maxNgramsExtracted = 100;
                    try {
                        Automaton automaton = new RegExp(reg.toLowerCase(Locale.ENGLISH), RegExp.ALL ^ RegExp.AUTOMATON).toAutomaton(maxDeterminizedStates);
                        NGramExtractor extractor = new NGramExtractor(3, maxExpand, maxStatesTraced, maxNgramsExtracted);
                        int clauses = extractor.extract(automaton).countClauses();
                        sum += clauses;
                        total++;
                        
                        if(clauses > 1024) {
                            above1024++;
                            regexes.put(line, clauses);
                        }
                    } catch(IllegalArgumentException iae) {
                        System.out.println(iae);
                        System.out.println(line + " : " + reg);
                    }
                }
            }
        }
        System.out.println("Regex above : " + above1024);
        System.out.println("Regex avg clauses : " + sum/total);
        for(Map.Entry<String, Integer> large : regexes.entrySet()) {
            System.out.println(large.getKey() + ", nb clauses: " + large.getValue());
        }
    }

Data set: /home/dcausse/insource/sample.txt