Too high cardinality is not suitable for dictionary!

Hi !
With building a cube faild, it throws some error.
```
[QuartzScheduler_Worker-22]:[2015-01-08 00:21:38,468][INFO][com.kylinolap.dict.DictionaryGenerator.buildDictionaryFromValueList(DictionaryGenerator.java:72)] - Dictionary cardinality 9999956
[QuartzScheduler_Worker-22]:[2015-01-08 00:21:38,468][ERROR][com.kylinolap.job.hadoop.dict.CreateDictionaryJob.run(CreateDictionaryJob.java:55)] - Too high cardinality is not suitable for dictionary! Are the values stable enough for incremental load??
java.lang.IllegalArgumentException: Too high cardinality is not suitable for dictionary! Are the values stable enough for incremental load??
at com.kylinolap.dict.DictionaryGenerator.buildDictionaryFromValueList(DictionaryGenerator.java:75)
at com.kylinolap.dict.DictionaryGenerator.buildDictionary(DictionaryGenerator.java:110)
at com.kylinolap.dict.DictionaryManager.buildDictionary(DictionaryManager.java:166)
at com.kylinolap.cube.CubeManager.buildDictionary(CubeManager.java:171)
```
in source code
```
/**

• @author yangli9
  */
  @SuppressWarnings( { "rawtypes", "unchecked" }

  )
  public class DictionaryGenerator {

private static final Logger logger = LoggerFactory.getLogger(DictionaryGenerator.class);

private static final String[] DATE_PATTERNS = new String[]

{ "yyyy-MM-dd" }

;

public static Dictionary<?> buildDictionaryFromValueList(DictionaryInfo info, List<byte[]> values) {
info.setCardinality(values.size());
...
// log a few samples
StringBuilder buf = new StringBuilder();
for (Object s : samples)

{ if (buf.length() > 0) buf.append(", "); buf.append(s.toString()).append("=>").append(dict.getIdFromValue(s)); }

logger.info("Dictionary value samples: " + buf.toString());
logger.info("Dictionary cardinality " + info.getCardinality());

if (values.size() > 1000000)
throw new IllegalArgumentException("Too high cardinality is not suitable for dictionary! Are the values stable enough for incremental load??");

return dict;
...
```
Here is limit to 1000000, what is it means?

---------------- Imported from GitHub ----------------
Url: https://github.com/KylinOLAP/Kylin/issues/364
Created by: Yancey1989
Labels:
Created at: Thu Jan 08 00:27:15 CST 2015
State: open