[GitHub] [arrow] marsupialtail commented on a diff in pull request #13640: ARROW-14635: [Python][C++] add O_DIRECT support to writes

[GitBox <gi...@apache.org>]

marsupialtail commented on code in PR #13640:
URL: https://github.com/apache/arrow/pull/13640#discussion_r924756597


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cpp/src/arrow/io/file.cc:
##########
@@ -378,6 +378,77 @@ Status FileOutputStream::Write(const void* data, int64_t length) {
 
 int FileOutputStream::file_descriptor() const { return impl_->fd(); }
 
+// ----------------------------------------------------------------------
+// DirectFileOutputStream, change the Open, Write and Close methods from FileOutputStream
+// Uses DirectIO for writes. Will only write out things in 4096 byte blocks. Buffers leftover bytes
+// in an internal data structure, which will be padded to 4096 bytes and flushed upon call to close.
+
+class DirectFileOutputStream::DirectFileOutputStreamImpl : public OSFile {
+ public:
+  Status Open(const std::string& path, bool append) {
+    const bool truncate = !append;
+    return OpenWritable(path, truncate, append, true /* write_only */, true);
+  }
+  Status Open(int fd) { return OpenWritable(fd); }
+};
+
+DirectFileOutputStream::DirectFileOutputStream() { 
+  uintptr_t mask = (uintptr_t)(4095);
+  uint8_t *mem = static_cast<uint8_t *>(malloc(4096 + 4095));
+  cached_data = reinterpret_cast<uint8_t *>( reinterpret_cast<uintptr_t>(mem+4095) & ~(mask));

Review Comment:
   Will produce some benchmark experiments that compare the posix_fadvise with O_DIRECT and link here.



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