wjhypo opened a new pull request #11307: URL: https://github.com/apache/druid/pull/11307
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See [the 'If your pull request shows conflicts with master' section](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#if-your-pull-request-shows-conflicts-with-master) for more details. --> Fixes #11301 <!-- If you are a committer, follow the PR action item checklist for committers: https://github.com/apache/druid/blob/master/dev/committer-instructions.md#pr-and-issue-action-item-checklist-for-committers. --> ### Description <!-- Describe the goal of this PR, what problem are you fixing. If there is a corresponding issue (referenced above), it's not necessary to repeat the description here, however, you may choose to keep one summary sentence. --> <!-- Describe your patch: what did you change in code? How did you fix the problem? --> <!-- If there are several relatively logically separate changes in this PR, create a mini-section for each of them. For example: --> - Choice of algorithms If `enableInMemoryBitmap` is set to true in `tuningConfig` in the supervisor spec, a bitmap is maintained during the data is in incremental index for each dimension that uses bitmap in the schema, i.e., for a dimension, only if bitmap is to be created when creating the immutable segment during handoff, will a corresponding temporary in memory bitmap be created. This in memory bitmap is not serialized or reused during persistence to completely separate from the other bitmap created in the immutable segment for clean logic separation. In terms of the implementation of this in memory bitmap, currently user can't specify it anywhere and only Roaring bitmap is used as the default implementation. The PR doesn't add choices to pick other compressed bitmaps like Concise Bitmap because we don't see clear performance benefits to add other implementations at the moment. In terms of the implementation of Roaring bitmap, there are 3 implementations available in the Roaring bitmap library: `MutableRoaringBitmap`, `ImmutableRoaringBitmap` and `RoaringBitmap`. `RoaringBitmap` is supposed to be more performant than the other two in this case because it doesn't need to maintain a byte buffer backend and byte buffer backend is only convenient if we need to do mmap or if there's serde involved, which is the case for batch ingested immutable segments querying. However, the implementation in the PR tries reusing the logic in the current classes built for the batch ingested immutable segments, so the byte buffer backed implementation `MutableRoaringBitmap` is used to store row indexes for each new rows. During query time, a snapshot of the bitmap is needed so `MutableRoaringBitmap` is cast to `ImmutableRoaringBitmap`, which involves copying at one of the stages of the conversion. During the copy, for high cardinality dimensions, the number of row indexes for a given row value should be small so the copying overhead should be minimal; for low cardinality dimensions, supposedly there are more data to copy than the previous case, we don't see obvious issue during testing and we can add metrics on the copying time and as long as the benefit outweigh the no bitmap full scan case, it should still be worthwhile. - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such as when there are insufficient resources? Step 1: enable in memory bitmap construction in supervisor spec ``` { "type": "kafka", "tuningConfig": { ... "enableInMemoryBitmap": true ... } } ``` Step 2: during query time, add a flag in query context (default is false) to determine if to use the in memory bitmap index (if enabled in step 1): `"useInMemoryBitmapInQuery": true` If either configuration is `false` or not specified will not trigger the usage of in memory bitmap during query time. - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns) The implementation tries piggybacking on the bitmap query related classes of batch generated immutable segment index (QueryableIndex and its support classes) as much as possible to reduce duplicate work. <!-- - Method organization and design (how the logic is split between methods, parameters and return types) - Naming (class, method, API, configuration, HTTP endpoint, names of emitted metrics) --> <!-- It's good to describe an alternative design (or mention an alternative name) for every design (or naming) decision point and compare the alternatives with the designs that you've implemented (or the names you've chosen) to highlight the advantages of the chosen designs and names. --> <!-- If there was a discussion of the design of the feature implemented in this PR elsewhere (e. g. a "Proposal" issue, any other issue, or a thread in the development mailing list), link to that discussion from this PR description and explain what have changed in your final design compared to your original proposal or the consensus version in the end of the discussion. If something hasn't changed since the original discussion, you can omit a detailed discussion of those aspects of the design here, perhaps apart from brief mentioning for the sake of readability of this PR description. --> <!-- Some of the aspects mentioned above may be omitted for simple and small changes. <hr> ##### Key changed/added classes in this PR * `MyFoo` * `OurBar` * `TheirBaz` <hr> --> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. 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Linked related entities via Javadoc links. - [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader. - [x] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for [code coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md) is met. - [ ] added integration tests. - [x] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
