enhance: Use fdopen, fwrite to reduce direct syscall (#38157)

`File.Write` and `File.WriteInt` use `write`, which may be just direct
syscall in some systems. When mappding field data and write line by
line, this could cost lost of CPU time when the row number is large.

---------

Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>

internal/core/src/common/File.h

@@ -11,11 +11,13 @@
 
 #pragma once
 
+#include <cstdio>
 #include <string>
 #include "common/EasyAssert.h"
 #include "common/Types.h"
 #include "fmt/core.h"
 #include <fcntl.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 namespace milvus {
@@ -27,8 +29,8 @@ class File {
         file.fd_ = -1;
     }
     ~File() {
-        if (fd_ >= 0) {
-            close(fd_);
+        if (fs_ != nullptr) {
+            fclose(fs_);
         }
     }
 
@@ -63,6 +65,22 @@ class File {
         return write(fd_, &value, sizeof(value));
     }
 
+    ssize_t
+    FWrite(const void* buf, size_t size) {
+        return fwrite(buf, sizeof(char), size, fs_);
+    }
+
+    template <typename T, std::enable_if_t<std::is_integral_v<T>, int> = 0>
+    ssize_t
+    FWriteInt(T value) {
+        return fwrite(&value, 1, sizeof(value), fs_);
+    }
+
+    int
+    FFlush() {
+        return fflush(fs_);
+    }
+
     offset_t
     Seek(offset_t offset, int whence) {
         return lseek(fd_, offset, whence);
@@ -70,15 +88,22 @@ class File {
 
     void
     Close() {
-        close(fd_);
+        fclose(fs_);
+        fs_ = nullptr;
         fd_ = -1;
     }
 
  private:
     explicit File(int fd, const std::string& filepath)
         : fd_(fd), filepath_(filepath) {
+        fs_ = fdopen(fd_, "wb+");
+        AssertInfo(fs_ != nullptr,
+                   "failed to open file {}: {}",
+                   filepath,
+                   strerror(errno));
     }
     int fd_{-1};
+    FILE* fs_;
     std::string filepath_;
 };
 }  // namespace milvus

internal/core/src/mmap/Utils.h

@@ -102,12 +102,12 @@ WriteFieldData(File& file,
                     auto str =
                         static_cast<const std::string*>(data->RawValue(i));
                     ssize_t written_data_size =
-                        file.WriteInt<uint32_t>(uint32_t(str->size()));
+                        file.FWriteInt<uint32_t>(uint32_t(str->size()));
                     if (written_data_size != sizeof(uint32_t)) {
                         THROW_FILE_WRITE_ERROR
                     }
                     total_written += written_data_size;
-                    auto written_data = file.Write(str->data(), str->size());
+                    auto written_data = file.FWrite(str->data(), str->size());
                     if (written_data < str->size()) {
                         THROW_FILE_WRITE_ERROR
                     }
@@ -121,14 +121,14 @@ WriteFieldData(File& file,
                     indices.push_back(total_written);
                     auto padded_string =
                         static_cast<const Json*>(data->RawValue(i))->data();
-                    ssize_t written_data_size =
-                        file.WriteInt<uint32_t>(uint32_t(padded_string.size()));
+                    ssize_t written_data_size = file.FWriteInt<uint32_t>(
+                        uint32_t(padded_string.size()));
                     if (written_data_size != sizeof(uint32_t)) {
                         THROW_FILE_WRITE_ERROR
                     }
                     total_written += written_data_size;
                     ssize_t written_data =
-                        file.Write(padded_string.data(), padded_string.size());
+                        file.FWrite(padded_string.data(), padded_string.size());
                     if (written_data < padded_string.size()) {
                         THROW_FILE_WRITE_ERROR
                     }
@@ -142,7 +142,7 @@ WriteFieldData(File& file,
                     indices.push_back(total_written);
                     auto array = static_cast<const Array*>(data->RawValue(i));
                     ssize_t written =
-                        file.Write(array->data(), array->byte_size());
+                        file.FWrite(array->data(), array->byte_size());
                     if (written < array->byte_size()) {
                         THROW_FILE_WRITE_ERROR
                     }
@@ -158,7 +158,7 @@ WriteFieldData(File& file,
                         static_cast<const knowhere::sparse::SparseRow<float>*>(
                             data->RawValue(i));
                     ssize_t written =
-                        file.Write(vec->data(), vec->data_byte_size());
+                        file.FWrite(vec->data(), vec->data_byte_size());
                     if (written < vec->data_byte_size()) {
                         break;
                     }
@@ -173,7 +173,7 @@ WriteFieldData(File& file,
         }
     } else {
         // write as: data|data|data|data|data|data......
-        size_t written = file.Write(data->Data(), data->DataSize());
+        size_t written = file.FWrite(data->Data(), data->DataSize());
         if (written < data->DataSize()) {
             THROW_FILE_WRITE_ERROR
         }
@@ -191,5 +191,6 @@ WriteFieldData(File& file,
             valid_data.push_back(data->is_valid(i));
         }
     }
+    file.FFlush();
 }
 }  // namespace milvus