Refactor SparsePageSource, delete cache files after use #5321
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trivialfis
reviewed
Feb 18, 2020
| @@ -300,77 +327,118 @@ class SparsePageSource : public DataSource<T> { | |||
| writer.PushWrite(std::move(page)); | |||
| } | |||
| std::unique_ptr<dmlc::Stream> fo( | |||
| dmlc::Stream::Create(cinfo.name_info.c_str(), "w")); | |||
| dmlc::Stream::Create(cache_info_.name_info.c_str(), "w")); | |||
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Can we add a check to make sure this file doesn't exist? There is a FileExists function in tests/cpp/helpers.h we can use.
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The ThreadedIterator is not thread safe, we should be very careful about stateful operations.
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I added fatal errors if cache exists or if multiple threads try to use the prefetcher. Please take a look at my test for threads. It's not technically 100% guaranteed to trigger the exception, we can remove the test if we get false negatives in CI.
trivialfis
approved these changes
Feb 19, 2020
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This refactoring separates out many of the components used in the external memory dmatrix. In particular the prefetching and management of pages is extracted into
ExternalMemoryPrefetcher<T>and different external memory page types all have their own constructors now.Part of the reason for doing this is to manage the lifetime of the cache files and remove them when the DMatrix gets destructed. Discussion about this in #4237. Leaving behind cache files leads to many unpredictable and unwanted behaviours, for example if I train the first time using 10% of my data, then train a second time using 100% but do not change the cache prefix, the 10% data will get loaded and used, completely ignoring the training input from the second run.