[kernel-spark] Add flatMap to CloseableIterator.java to support lazy loading of delta log changes. #5650
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This was referenced Dec 8, 2025
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…for dsv2 streaming (#5499) ## 🥞 Stacked PR Use this [link](https://github.com/delta-io/delta/pull/5499/files) to review incremental changes. - [**stack/plan1**](#5499) [[Files changed](https://github.com/delta-io/delta/pull/5499/files)] - [stack/integration](#5572) [[Files changed](https://github.com/delta-io/delta/pull/5572/files/a0512bb563ff00a31461c2a188e11d59f19146e1..321432605fc1efe3253b30116de2d389f6f66977)] - [stack/integration2](#5652) [[Files changed](https://github.com/delta-io/delta/pull/5652/files/321432605fc1efe3253b30116de2d389f6f66977..dee64c4ca3abbdd530c232e42325e702e9d61a0b)] - [stack/reader](#5638) [[Files changed](https://github.com/delta-io/delta/pull/5638/files/dee64c4ca3abbdd530c232e42325e702e9d61a0b..c8f25572585682e9d540bce0c4e982dc8dc1079c)] - [stack/lazy](#5650) [[Files changed](https://github.com/delta-io/delta/pull/5650/files/c8f25572585682e9d540bce0c4e982dc8dc1079c..0703f5750fa765d45c5b8c04b286d05f87e0ac6c)] - [stack/snapshot](#5651) [[Files changed](https://github.com/delta-io/delta/pull/5651/files/0703f5750fa765d45c5b8c04b286d05f87e0ac6c..cb6efb41f4cf62ec1501f6b7dce5e8d6e926eaf1)] --------- <!-- Thanks for sending a pull request! Here are some tips for you: 1. If this is your first time, please read our contributor guidelines: https://github.com/delta-io/delta/blob/master/CONTRIBUTING.md 2. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP] Your PR title ...'. 3. Be sure to keep the PR description updated to reflect all changes. 4. Please write your PR title to summarize what this PR proposes. 5. If possible, provide a concise example to reproduce the issue for a faster review. 6. If applicable, include the corresponding issue number in the PR title and link it in the body. --> #### Which Delta project/connector is this regarding? <!-- Please add the component selected below to the beginning of the pull request title For example: [Spark] Title of my pull request --> - [x] Spark - [ ] Standalone - [ ] Flink - [ ] Kernel - [ ] Other (fill in here) ## Description <!-- - Describe what this PR changes. - Describe why we need the change. If this PR resolves an issue be sure to include "Resolves #XXX" to correctly link and close the issue upon merge. --> In this PR, we implement the DSv2 methods `planInputPartitions()` and `createReaderFactory()`. These are DSv2-only API that will replace DSv1's `getBatch()` `planInputPartitions()`: Returns physical partitions describing how to read the data; Called once per micro-batch during planning `createReaderFactory()`: Returns a factory that creates readers for the partitions; Each executor uses this factory to read its assigned partitions ## How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to test the changes thoroughly including negative and positive cases if possible. If the changes were tested in any way other than unit tests, please clarify how you tested step by step (ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future). If the changes were not tested, please explain why. --> ## Does this PR introduce _any_ user-facing changes? <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If possible, please also clarify if this is a user-facing change compared to the released Delta Lake versions or within the unreleased branches such as master. If no, write 'No'. -->
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…for dsv2 streaming (delta-io#5499) ## 🥞 Stacked PR Use this [link](https://github.com/delta-io/delta/pull/5499/files) to review incremental changes. - [**stack/plan1**](delta-io#5499) [[Files changed](https://github.com/delta-io/delta/pull/5499/files)] - [stack/integration](delta-io#5572) [[Files changed](https://github.com/delta-io/delta/pull/5572/files/a0512bb563ff00a31461c2a188e11d59f19146e1..321432605fc1efe3253b30116de2d389f6f66977)] - [stack/integration2](delta-io#5652) [[Files changed](https://github.com/delta-io/delta/pull/5652/files/321432605fc1efe3253b30116de2d389f6f66977..dee64c4ca3abbdd530c232e42325e702e9d61a0b)] - [stack/reader](delta-io#5638) [[Files changed](https://github.com/delta-io/delta/pull/5638/files/dee64c4ca3abbdd530c232e42325e702e9d61a0b..c8f25572585682e9d540bce0c4e982dc8dc1079c)] - [stack/lazy](delta-io#5650) [[Files changed](https://github.com/delta-io/delta/pull/5650/files/c8f25572585682e9d540bce0c4e982dc8dc1079c..0703f5750fa765d45c5b8c04b286d05f87e0ac6c)] - [stack/snapshot](delta-io#5651) [[Files changed](https://github.com/delta-io/delta/pull/5651/files/0703f5750fa765d45c5b8c04b286d05f87e0ac6c..cb6efb41f4cf62ec1501f6b7dce5e8d6e926eaf1)] --------- <!-- Thanks for sending a pull request! Here are some tips for you: 1. If this is your first time, please read our contributor guidelines: https://github.com/delta-io/delta/blob/master/CONTRIBUTING.md 2. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP] Your PR title ...'. 3. Be sure to keep the PR description updated to reflect all changes. 4. Please write your PR title to summarize what this PR proposes. 5. If possible, provide a concise example to reproduce the issue for a faster review. 6. If applicable, include the corresponding issue number in the PR title and link it in the body. --> #### Which Delta project/connector is this regarding? <!-- Please add the component selected below to the beginning of the pull request title For example: [Spark] Title of my pull request --> - [x] Spark - [ ] Standalone - [ ] Flink - [ ] Kernel - [ ] Other (fill in here) ## Description <!-- - Describe what this PR changes. - Describe why we need the change. If this PR resolves an issue be sure to include "Resolves #XXX" to correctly link and close the issue upon merge. --> In this PR, we implement the DSv2 methods `planInputPartitions()` and `createReaderFactory()`. These are DSv2-only API that will replace DSv1's `getBatch()` `planInputPartitions()`: Returns physical partitions describing how to read the data; Called once per micro-batch during planning `createReaderFactory()`: Returns a factory that creates readers for the partitions; Each executor uses this factory to read its assigned partitions ## How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to test the changes thoroughly including negative and positive cases if possible. If the changes were tested in any way other than unit tests, please clarify how you tested step by step (ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future). If the changes were not tested, please explain why. --> ## Does this PR introduce _any_ user-facing changes? <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If possible, please also clarify if this is a user-facing change compared to the released Delta Lake versions or within the unreleased branches such as master. If no, write 'No'. -->
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| * @param <U> The type of elements in the resulting iterator | ||
| * @return A flattened {@link CloseableIterator} over all elements from all inner iterators | ||
| */ | ||
| default <U> CloseableIterator<U> flatMap(Function<T, CloseableIterator<U>> mapper) { |
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Can you separate kernel changes in an isolated PR?
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…r dsv2 streaming (#5572) ## 🥞 Stacked PR Use this [link](https://github.com/delta-io/delta/pull/5572/files) to review incremental changes. - [**stack/integration**](#5572) [[Files changed](https://github.com/delta-io/delta/pull/5572/files)] - [stack/integration2](#5652) [[Files changed](https://github.com/delta-io/delta/pull/5652/files/6bae6e4ad461ef8ec4d5849c6ab70190b5c8e3c4..86dac519632a5acb21624b24b205d28d5bfb8e40)] - [stack/reader](#5638) [[Files changed](https://github.com/delta-io/delta/pull/5638/files/86dac519632a5acb21624b24b205d28d5bfb8e40..236b9425cddde4bf1a6155ff69666f3957b9bed2)] - [stack/lazy](#5650) [[Files changed](https://github.com/delta-io/delta/pull/5650/files/236b9425cddde4bf1a6155ff69666f3957b9bed2..08f8fe0046d45ebd955d78fa4c6ea8042248d46d)] - [stack/lazy2](#5686) [[Files changed](https://github.com/delta-io/delta/pull/5686/files/08f8fe0046d45ebd955d78fa4c6ea8042248d46d..45cb03377364de0d170969cff445bb86068e8557)] - [stack/snapshot](#5651) [[Files changed](https://github.com/delta-io/delta/pull/5651/files/45cb03377364de0d170969cff445bb86068e8557..bf0efa8312401fcee2e5fcc5301cf14df264a5c9)] --------- <!-- Thanks for sending a pull request! Here are some tips for you: 1. If this is your first time, please read our contributor guidelines: https://github.com/delta-io/delta/blob/master/CONTRIBUTING.md 2. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP] Your PR title ...'. 3. Be sure to keep the PR description updated to reflect all changes. 4. Please write your PR title to summarize what this PR proposes. 5. If possible, provide a concise example to reproduce the issue for a faster review. 6. If applicable, include the corresponding issue number in the PR title and link it in the body. --> #### Which Delta project/connector is this regarding? <!-- Please add the component selected below to the beginning of the pull request title For example: [Spark] Title of my pull request --> - [x] Spark - [ ] Standalone - [ ] Flink - [ ] Kernel - [ ] Other (fill in here) ## Description Implement `deserializeOffset`, `commit`, and `stop` methods in `SparkMicroBatchStream` to complete the Spark DSv2 streaming API contract. 1. **`deserializeOffset(json)`** - Called when resuming from a checkpoint. 2. **`commit(end)`** - Called after each micro-batch completes successfully. 3. **`stop()`** - Called during query shutdown. <!-- - Describe what this PR changes. - Describe why we need the change. If this PR resolves an issue be sure to include "Resolves #XXX" to correctly link and close the issue upon merge. --> ## How was this patch tested? Unit tests <!-- If tests were added, say they were added here. Please make sure to test the changes thoroughly including negative and positive cases if possible. If the changes were tested in any way other than unit tests, please clarify how you tested step by step (ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future). If the changes were not tested, please explain why. --> ## Does this PR introduce _any_ user-facing changes? No. <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If possible, please also clarify if this is a user-facing change compared to the released Delta Lake versions or within the unreleased branches such as master. If no, write 'No'. -->
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🥞 Stacked PR
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Which Delta project/connector is this regarding?
Description
This PR refactors
SparkMicroBatchStream.filterDeltaLogsto use lazy iteration instead of eagerly loading allIndexedFileentries into memory.Added
flatMaptoCloseableIterator: A new method that transforms each element into an iterator and flattens the results, enabling lazy processing of nested iterables.The previous implementation loaded all file changes into memory before returning the iterator. With lazy loading, files are processed incrementally as the iterator is consumed, reducing memory pressure for large batches spanning many commits or files.
How was this patch tested?
Existing unit tests for streaming functionality.
Does this PR introduce any user-facing changes?
No