Update upper_bound_offset when reseek changes iterate_upper_bound dynamically (#11775)

Summary:
Update the logic in FilePrefetchBuffer to update `upper_bound_offset_` during reseek. During Reseek, `iterate_upper_bound` can be changed dynamically. So added an API to update that in FilePrefetchBuffer.
Added unit test to confirm the behavior.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11775

Test Plan:
- Check stress tests in case there is any failure after this diff.
- make crash_test -j32 with auto_readahead_size=1 passed locally

Reviewed By: anand1976

Differential Revision: D48815177

Pulled By: akankshamahajan15

fbshipit-source-id: 5f44fbb3af06c86a1c38f139c5fa4543891837f4

file/file_prefetch_buffer.h

@@ -279,6 +279,11 @@ class FilePrefetchBuffer {
   // Callback function passed to underlying FS in case of asynchronous reads.
   void PrefetchAsyncCallback(const FSReadRequest& req, void* cb_arg);
 
+  void ResetUpperBoundOffset(uint64_t upper_bound_offset) {
+    upper_bound_offset_ = upper_bound_offset;
+    readahead_size_ = initial_auto_readahead_size_;
+  }
+
  private:
   // Calculates roundoff offset and length to be prefetched based on alignment
   // and data present in buffer_. It also allocates new buffer or refit tail if
@@ -321,7 +326,6 @@ class FilePrefetchBuffer {
   void ResetValues() {
     num_file_reads_ = 1;
     readahead_size_ = initial_auto_readahead_size_;
-    upper_bound_offset_ = 0;
   }
 
   // Called in case of implicit auto prefetching.

file/prefetch_test.cc

@@ -2082,6 +2082,7 @@ TEST_P(PrefetchTest, IterReadAheadSizeWithUpperBound) {
 
     int buff_count_with_tuning = 0, buff_count_without_tuning = 0;
     int keys_with_tuning = 0, keys_without_tuning = 0;
+    int reseek_keys_with_tuning = 0, reseek_keys_without_tuning = 0;
     buff_prefetch_count = 0;
 
     SyncPoint::GetInstance()->SetCallBack(
@@ -2102,17 +2103,19 @@ TEST_P(PrefetchTest, IterReadAheadSizeWithUpperBound) {
       ropts.async_io = true;
     }
 
-    Slice ub = Slice("my_key_uuu");
-    ropts.iterate_upper_bound = &ub;
-    Slice seek_key = Slice("my_key_aaa");
-
     // With tuning readahead_size.
     {
       ASSERT_OK(options.statistics->Reset());
+      Slice ub = Slice("my_key_uuu");
+      Slice* ub_ptr = &ub;
+      ropts.iterate_upper_bound = ub_ptr;
       ropts.auto_readahead_size = true;
 
       auto iter = std::unique_ptr<Iterator>(db_->NewIterator(ropts));
 
+      // Seek.
+      {
+        Slice seek_key = Slice("my_key_aaa");
         iter->Seek(seek_key);
 
         while (iter->Valid()) {
@@ -2120,20 +2123,44 @@ TEST_P(PrefetchTest, IterReadAheadSizeWithUpperBound) {
           iter->Next();
         }
 
-      uint64_t readhahead_trimmed =
+        uint64_t readahead_trimmed =
             options.statistics->getAndResetTickerCount(READAHEAD_TRIMMED);
-      ASSERT_GT(readhahead_trimmed, 0);
+        ASSERT_GT(readahead_trimmed, 0);
         buff_count_with_tuning = buff_prefetch_count;
       }
 
+      // Reseek with new upper_bound_iterator.
+      {
+        ub = Slice("my_key_y");
+        Slice reseek_key = Slice("my_key_v");
+        iter->Seek(reseek_key);
+
+        while (iter->Valid()) {
+          iter->Next();
+          reseek_keys_with_tuning++;
+        }
+
+        uint64_t readahead_trimmed =
+            options.statistics->getAndResetTickerCount(READAHEAD_TRIMMED);
+        ASSERT_GT(readahead_trimmed, 0);
+        ASSERT_GT(reseek_keys_with_tuning, 0);
+      }
+    }
+
     // Without tuning readahead_size
     {
+      Slice ub = Slice("my_key_uuu");
+      Slice* ub_ptr = &ub;
+      ropts.iterate_upper_bound = ub_ptr;
       buff_prefetch_count = 0;
       ASSERT_OK(options.statistics->Reset());
       ropts.auto_readahead_size = false;
 
       auto iter = std::unique_ptr<Iterator>(db_->NewIterator(ropts));
 
+      // Seek.
+      {
+        Slice seek_key = Slice("my_key_aaa");
         iter->Seek(seek_key);
 
         while (iter->Valid()) {
@@ -2141,9 +2168,27 @@ TEST_P(PrefetchTest, IterReadAheadSizeWithUpperBound) {
           iter->Next();
         }
         buff_count_without_tuning = buff_prefetch_count;
-      uint64_t readhahead_trimmed =
+        uint64_t readahead_trimmed =
             options.statistics->getAndResetTickerCount(READAHEAD_TRIMMED);
-      ASSERT_EQ(readhahead_trimmed, 0);
+        ASSERT_EQ(readahead_trimmed, 0);
+      }
+
+      // Reseek with new upper_bound_iterator.
+      {
+        ub = Slice("my_key_y");
+        Slice reseek_key = Slice("my_key_v");
+        iter->Seek(reseek_key);
+
+        while (iter->Valid()) {
+          iter->Next();
+          reseek_keys_without_tuning++;
+        }
+
+        uint64_t readahead_trimmed =
+            options.statistics->getAndResetTickerCount(READAHEAD_TRIMMED);
+        ASSERT_EQ(readahead_trimmed, 0);
+        ASSERT_GT(reseek_keys_without_tuning, 0);
+      }
     }
 
     {
@@ -2159,6 +2204,8 @@ TEST_P(PrefetchTest, IterReadAheadSizeWithUpperBound) {
       ASSERT_GT(buff_count_with_tuning, 0);
       // No of keys should be equal.
       ASSERT_EQ(keys_without_tuning, keys_with_tuning);
+      // No of keys after reseek with new upper bound should be equal.
+      ASSERT_EQ(reseek_keys_without_tuning, reseek_keys_with_tuning);
     }
     Close();
   }

table/block_based/block_prefetcher.h

@@ -55,6 +55,11 @@ class BlockPrefetcher {
 
   void SetUpperBoundOffset(uint64_t upper_bound_offset) {
     upper_bound_offset_ = upper_bound_offset;
+    if (prefetch_buffer() != nullptr) {
+      // Upper bound can be changed on reseek. So update that in
+      // FilePrefetchBuffer.
+      prefetch_buffer()->ResetUpperBoundOffset(upper_bound_offset);
+    }
   }
 
  private:

unreleased_history/bug_fixes/upper_bound_autoreadahead.md

@@ -0,0 +1 @@
+* When auto_readahead_size is enabled, update readahead upper bound during readahead trimming when reseek changes iterate_upper_bound dynamically.