Better

src/Disks/IO/AsynchronousReadIndirectBufferFromRemoteFS.cpp

@@ -56,31 +56,20 @@ String AsynchronousReadIndirectBufferFromRemoteFS::getFileName() const
 }
 
 
-size_t AsynchronousReadIndirectBufferFromRemoteFS::getNumBytesToRead()
+bool AsynchronousReadIndirectBufferFromRemoteFS::hasPendingDataToRead()
 {
-    size_t num_bytes_to_read;
-
     /// Position is set only for MergeTree tables.
     if (read_until_position)
     {
         /// Everything is already read.
-        if (file_offset_of_buffer_end == *read_until_position)
-            return 0;
+        if (file_offset_of_buffer_end == read_until_position)
+            return false;
 
-        if (file_offset_of_buffer_end > *read_until_position)
+        if (file_offset_of_buffer_end > read_until_position)
             throw Exception(ErrorCodes::LOGICAL_ERROR, "Read beyond last offset ({} > {})",
-                            file_offset_of_buffer_end, *read_until_position);
-
-        /// Read range [file_offset_of_buffer_end, read_until_position).
-        num_bytes_to_read = *read_until_position - file_offset_of_buffer_end;
-        num_bytes_to_read = std::min(num_bytes_to_read, internal_buffer.size());
+                            file_offset_of_buffer_end, read_until_position);
     }
-    else
-    {
-        num_bytes_to_read = internal_buffer.size();
-    }
-
-    return num_bytes_to_read;
+    return true;
 }
 
 
@@ -107,12 +96,10 @@ void AsynchronousReadIndirectBufferFromRemoteFS::prefetch()
     if (prefetch_future.valid())
         return;
 
-    auto num_bytes_to_read = getNumBytesToRead();
-    if (!num_bytes_to_read)
+    if (!hasPendingDataToRead())
         return;
 
     /// Prefetch even in case hasPendingData() == true.
-    prefetch_buffer.resize(num_bytes_to_read);
     prefetch_future = readInto(prefetch_buffer.data(), prefetch_buffer.size());
     ProfileEvents::increment(ProfileEvents::RemoteFSPrefetches);
 }
@@ -130,6 +117,9 @@ void AsynchronousReadIndirectBufferFromRemoteFS::setReadUntilPosition(size_t pos
 
 bool AsynchronousReadIndirectBufferFromRemoteFS::nextImpl()
 {
+    if (!hasPendingDataToRead())
+        return false;
+
     size_t size = 0;
 
     if (prefetch_future.valid())
@@ -154,12 +144,8 @@ bool AsynchronousReadIndirectBufferFromRemoteFS::nextImpl()
     }
     else
     {
-        auto num_bytes_to_read = getNumBytesToRead();
-        if (!num_bytes_to_read) /// Nothing to read.
-            return false;
-
         ProfileEvents::increment(ProfileEvents::RemoteFSUnprefetchedReads);
-        size = readInto(memory.data(), num_bytes_to_read).get();
+        size = readInto(memory.data(), memory.size()).get();
 
         if (size)
         {

src/Disks/IO/AsynchronousReadIndirectBufferFromRemoteFS.h

@@ -54,7 +54,7 @@ private:
 
     void finalize();
 
-    size_t getNumBytesToRead();
+    bool hasPendingDataToRead();
 
     std::future<IAsynchronousReader::Result> readInto(char * data, size_t size);
 
@@ -74,7 +74,7 @@ private:
 
     size_t bytes_to_ignore = 0;
 
-    std::optional<size_t> read_until_position = 0;
+    size_t read_until_position = 0;
 };
 
 }

src/IO/AsynchronousReadBufferFromFileDescriptor.cpp

@@ -57,15 +57,15 @@ size_t AsynchronousReadBufferFromFileDescriptor::getNumBytesToRead()
     if (read_until_position)
     {
         /// Everything is already read.
-        if (file_offset_of_buffer_end == *read_until_position)
+        if (file_offset_of_buffer_end == read_until_position)
             return 0;
 
-        if (file_offset_of_buffer_end > *read_until_position)
+        if (file_offset_of_buffer_end > read_until_position)
             throw Exception(ErrorCodes::LOGICAL_ERROR, "Read beyond last offset ({} > {})",
-                            file_offset_of_buffer_end, *read_until_position);
+                            file_offset_of_buffer_end, read_until_position);
 
         /// Read range [file_offset_of_buffer_end, read_until_position).
-        num_bytes_to_read = *read_until_position - file_offset_of_buffer_end;
+        num_bytes_to_read = read_until_position - file_offset_of_buffer_end;
         num_bytes_to_read = std::min(num_bytes_to_read, internal_buffer.size());
     }
     else

src/IO/AsynchronousReadBufferFromFileDescriptor.h

@@ -24,7 +24,7 @@ protected:
 
     const size_t required_alignment = 0;  /// For O_DIRECT both file offsets and memory addresses have to be aligned.
     size_t file_offset_of_buffer_end = 0; /// What offset in file corresponds to working_buffer.end().
-    std::optional<size_t> read_until_position;
+    size_t read_until_position = 0;
     int fd;
 
     bool nextImpl() override;