[ https://issues.apache.org/jira/browse/KYLIN-1186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15112096#comment-15112096 ]
liyang commented on KYLIN-1186: ------------------------------- This is great patch. Please go ahead with the merge. We use `git rebase` to ensure a streamline of commits. Some very minor comments. - in BitmapSerializer.maxLength(), the comment says 32 MB, but the code returns 8 MB. - in BitmapSerializer.getStocd rageBytesEstimate(), the result should be an estimate of the average size in bytes (I'm updating the javadoc) Thanks Yerui! > Support precise Count Distinct using bitmap > ------------------------------------------- > > Key: KYLIN-1186 > URL: https://issues.apache.org/jira/browse/KYLIN-1186 > Project: Kylin > Issue Type: Improvement > Components: Job Engine > Affects Versions: v1.1 > Reporter: Yerui Sun > Assignee: Yerui Sun > Fix For: v2.0, v1.3 > > Attachments: KYLIN-1186-1.x-staging.2.patch, > KYLIN-1186-1.x-staging.patch, KYLIN-1186-2.x-staging.2.patch, > KYLIN-1186-2.x-staging.3.patch > > Original Estimate: 168h > Remaining Estimate: 168h > > For now, kylin only support non-precise count distinct by hyperloglog. > In our production scenario, there're strongly requirements for precise count > distinct, mainly for the column of type int or bigint, such as user-id, > product-id, etc. > Implementing of precise count distinct for all types is difficult and not > efficiency. However, only supporting int or bigint make this much easier. The > values can be projected into a bitmap, which is easy to be compressed and > stored, and easy to count. > I've created a POC based on RoaringBitmap, proving that worked. There's some > more work to be done: > * RoaringBitmap only support int, there need a solution to support bigint; > * Add a new measure and codec, like HyperLogLogPlusCounter, make it easy to > use; > * Add new measure on web ui, and check that whether the column type is int > or bigint; -- This message was sent by Atlassian JIRA (v6.3.4#6332)