From 01298c8ff7c7b94022014b72b95baca29eef3ddc Mon Sep 17 00:00:00 2001
From: anand76 <anand76@devvm1373.frc2.facebook.com>
Date: Wed, 30 Dec 2020 09:24:04 -0800
Subject: [PATCH] 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 | 6 +++++-
 file/file_prefetch_buffer.h  | 2 +-
 file/file_util.cc            | 2 +-
 table/block_fetcher.cc       | 5 ++++-
 table/format.cc              | 5 +++--
 table/table_test.cc          | 6 +++---
 6 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/file/file_prefetch_buffer.cc b/file/file_prefetch_buffer.cc
index ce98177be..218983254 100644
--- a/file/file_prefetch_buffer.cc
+++ b/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
diff --git a/file/file_prefetch_buffer.h b/file/file_prefetch_buffer.h
index d8e9c0ff6..5532e79df 100644
--- a/file/file_prefetch_buffer.h
+++ b/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.
diff --git a/file/file_util.cc b/file/file_util.cc
index 451ef7728..4e92673d6 100644
--- a/file/file_util.cc
+++ b/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) {
diff --git a/table/block_fetcher.cc b/table/block_fetcher.cc
index b0880d516..e9df0f7af 100644
--- a/table/block_fetcher.cc
+++ b/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_;
diff --git a/table/format.cc b/table/format.cc
index 8fb66f8a1..b87274700 100644
--- a/table/format.cc
+++ b/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);
diff --git a/table/table_test.cc b/table/table_test.cc
index bfec7b79b..db765d483 100644
--- a/table/table_test.cc
+++ b/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());
 }