The dimension dictionary is a legacy design for HBase storage I think; because HBase has no data type, everything is a byte array, this makes Kylin has to encode STRING and other types with some encoding method like the dictionary.
Now with the storage like Parquet, it would decide how to encode the data at the page or block level. Then we can drop the dictionary after the cube is built. This will release the memory pressure of Kylin query nodes and also benefit the UHC case. Best regards, Shaofeng Shi 史少锋 Apache Kylin PMC Work email: [email protected] Kyligence Inc: https://kyligence.io/ Apache Kylin FAQ: https://kylin.apache.org/docs/gettingstarted/faq.html Join Kylin user mail group: [email protected] Join Kylin dev mail group: [email protected] Chao Long <[email protected]> 于2018年12月17日周一 下午1:23写道： > In this PoC, we verified Kylin On Parquet is viable, but the query > performance still have room to improve. We can improve it from the > following aspects: > > 1, Minimize result set serialization time > Since Kylin need Object[] data to process, we convert Dataset to RDD, and > then convert the "Row" type to Object[], so Spark need to serialize > Object[] before return it to driver. Those time need to be avoided. > > 2, Query without dictionary > In this PoC, for less storage use, we keep dict encode value in Parquet > file for dict-encode dimensions, so Kylin must load dictionary to convert > dict value for query. If we keep original value for dict-encode dimension, > dictionary is unnecessary. And we don't hava to worry about the storage > use, because Parquet will encode it. We should remove dictionary from query. > > 3, Remove query single-point issue > In this PoC, we use Spark to read and process Cube data, which is > distributed, but kylin alse need to process result data the Spark returned > in single jvm. We can try to make it distributed too. > > 4, Upgrade Parquet to 1.11 for page index > In this PoC, Parquet don't have page index, we get a poor filter > performance. We need to upgrade Parquet to version 1.11 which has page > index to improve filter performance. > > ------------------ > Best Regards, > Chao Long > > ------------------ 原始邮件 ------------------ > *发件人:* "ShaoFeng Shi"<[email protected]>; > *发送时间:* 2018年12月14日(星期五) 下午4:39 > *收件人:* "dev"<[email protected]>;"user"<[email protected]>; > *主题:* Evaluate Kylin on Parquet > > Hello Kylin users, > > The first version of Kylin on Parquet [1] feature has been staged in Kylin > code repository for public review and evaluation. You can check out the > "kylin-on-parquet" branch [2] to read the code, and also can make a binary > build to run an example. When creating a cube, you can select "Parquet" as > the storage in the "Advanced setting" page. Both MapReduce and Spark > engines support this new storage. A tech blog is under drafting for the > design and implementation. > > Thanks so much to the engineers' hard work: Chao Long and Yichen Zhou! > > This is not the final version; there is room to improve in many aspects, > parquet, spark, and Kylin. It can be used for PoC at this moment. Your > comments are welcomed. Let's improve it together. > > [1] https://issues.apache.org/jira/browse/KYLIN-3621 > [2] https://github.com/apache/kylin/tree/kylin-on-parquet > > Best regards, > > Shaofeng Shi 史少锋 > Apache Kylin PMC > Work email: [email protected] > Kyligence Inc: https://kyligence.io/ > > Apache Kylin FAQ: https://kylin.apache.org/docs/gettingstarted/faq.html > Join Kylin user mail group: [email protected] > Join Kylin dev mail group: [email protected] > > >
