Return Status from FilePrefetchBuffer::TryReadFromCache() (#7816)

Summary:
Return the Status from TryReadFromCache() in an argument to make it easier to report prefetch errors to the user.

Tests:
make crash_test
make check

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7816

Reviewed By: akankshamahajan15

Differential Revision: D25717222

Pulled By: anand1976

fbshipit-source-id: c320d3c12d4146bda16df78ff6927eee584c1810

file/file_prefetch_buffer.cc

@@ -109,7 +109,8 @@ Status FilePrefetchBuffer::Prefetch(const IOOptions& opts,
 
 bool FilePrefetchBuffer::TryReadFromCache(const IOOptions& opts,
                                           uint64_t offset, size_t n,
-                                          Slice* result, bool for_compaction) {
+                                          Slice* result, Status* status,
+                                          bool for_compaction) {
   if (track_min_offset_ && offset < min_offset_read_) {
     min_offset_read_ = static_cast<size_t>(offset);
   }
@@ -134,6 +135,9 @@ bool FilePrefetchBuffer::TryReadFromCache(const IOOptions& opts,
                      for_compaction);
       }
       if (!s.ok()) {
+        if (status) {
+          *status = s;
+        }
 #ifndef NDEBUG
         IGNORE_STATUS_IF_ERROR(s);
 #endif

file/file_prefetch_buffer.h

@@ -75,7 +75,7 @@ class FilePrefetchBuffer {
   // result : output buffer to put the data into.
   // for_compaction : if cache read is done for compaction read.
   bool TryReadFromCache(const IOOptions& opts, uint64_t offset, size_t n,
-                        Slice* result, bool for_compaction = false);
+                        Slice* result, Status* s, bool for_compaction = false);
 
   // The minimum `offset` ever passed to TryReadFromCache(). This will nly be
   // tracked if track_min_offset = true.

file/file_util.cc

@@ -195,7 +195,7 @@ IOStatus GenerateOneFileChecksum(
     size_t bytes_to_read =
         static_cast<size_t>(std::min(uint64_t{readahead_size}, size));
     if (!prefetch_buffer.TryReadFromCache(opts, offset, bytes_to_read, &slice,
-                                          false)) {
+                                          nullptr, false)) {
       return IOStatus::Corruption("file read failed");
     }
     if (slice.size() == 0) {

table/block_fetcher.cc

@@ -63,13 +63,16 @@ inline bool BlockFetcher::TryGetFromPrefetchBuffer() {
     Status s = PrepareIOFromReadOptions(read_options_, file_->env(), opts);
     if (s.ok() && prefetch_buffer_->TryReadFromCache(
                       opts, handle_.offset(), block_size_with_trailer_, &slice_,
-                      for_compaction_)) {
+                      &s, for_compaction_)) {
       CheckBlockChecksum();
       if (!status_.ok()) {
         return true;
       }
       got_from_prefetch_buffer_ = true;
       used_buf_ = const_cast<char*>(slice_.data());
+    } else if (!s.ok()) {
+      status_ = s;
+      return true;
     }
   }
   return got_from_prefetch_buffer_;

table/format.cc

@@ -307,8 +307,9 @@ Status ReadFooterFromFile(const IOOptions& opts, RandomAccessFileReader* file,
   // for iterator, TryReadFromCache might do a readahead. Revisit to see if we
   // need to pass a timeout at that point
   if (prefetch_buffer == nullptr ||
-      !prefetch_buffer->TryReadFromCache(
-          IOOptions(), read_offset, Footer::kMaxEncodedLength, &footer_input)) {
+      !prefetch_buffer->TryReadFromCache(IOOptions(), read_offset,
+                                         Footer::kMaxEncodedLength,
+                                         &footer_input, nullptr)) {
     if (file->use_direct_io()) {
       s = file->Read(opts, read_offset, Footer::kMaxEncodedLength,
                      &footer_input, nullptr, &internal_buf);

table/table_test.cc

@@ -4559,9 +4559,9 @@ TEST_F(BBTTailPrefetchTest, FilePrefetchBufferMinOffset) {
   TailPrefetchStats tpstats;
   FilePrefetchBuffer buffer(nullptr, 0, 0, false, true);
   IOOptions opts;
-  buffer.TryReadFromCache(opts, 500, 10, nullptr);
-  buffer.TryReadFromCache(opts, 480, 10, nullptr);
-  buffer.TryReadFromCache(opts, 490, 10, nullptr);
+  buffer.TryReadFromCache(opts, 500, 10, nullptr, nullptr);
+  buffer.TryReadFromCache(opts, 480, 10, nullptr, nullptr);
+  buffer.TryReadFromCache(opts, 490, 10, nullptr, nullptr);
   ASSERT_EQ(480, buffer.min_offset_read());
 }