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由 Siying Dong 提交于
Summary: Right now, if direct I/O is enabled, prefetching the last 512KB cannot be applied, except compaction inputs or readahead is enabled for iterators. This can create a lot of I/O for HDD cases. To solve the problem, the 512KB is prefetched in block based table if direct I/O is enabled. The prefetched buffer is passed in totegher with random access file reader, so that we try to read from the buffer before reading from the file. This can be extended in the future to support flexible user iterator readahead too. Closes https://github.com/facebook/rocksdb/pull/2708 Differential Revision: D5593091 Pulled By: siying fbshipit-source-id: ee36ff6d8af11c312a2622272b21957a7b5c81e7
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