Avoid shifting component too large error in FileTtlBooster (#11673)

Summary:
When `num_levels` > 65, we may be shifting more than 63 bits in FileTtlBooster. This can give errors like: `runtime error: shift exponent 98 is too large for 64-bit type 'uint64_t' (aka 'unsigned long')`. This PR makes a quick fix for this issue by taking a min in the shifting component. This issue should be rare since it requires a user using a large `num_levels`. I'll follow up with a more complex fix if needed.

Pull Request resolved: #11673

Test Plan: * Add a unit test that produce the above error before this PR. Need to compile it with ubsan: `COMPILE_WITH_UBSAN=1 OPT="-fsanitize-blacklist=.circleci/ubsan_suppression_list.txt" ROCKSDB_DISABLE_ALIGNED_NEW=1 USE_CLANG=1 make V=1 -j32 compaction_picker_test`

Reviewed By: hx235

Differential Revision: D48074386

Pulled By: cbi42

fbshipit-source-id: 25e59df7e93f20e0793cffb941de70ac815d9392

db/compaction/compaction_picker_test.cc

@@ -1968,6 +1968,15 @@ TEST_F(CompactionPickerTest, OverlappingUserKeys11) {
   ASSERT_EQ(7U, compaction->input(1, 0)->fd.GetNumber());
 }
 
+TEST_F(CompactionPickerTest, FileTtlBoosterLargeNumLevels) {
+  const uint64_t kCurrentTime = 1000000;
+  FileTtlBooster booster(kCurrentTime, /*ttl=*/2048,
+                         /*num_non_empty_levels=*/100, /*level=*/1);
+  FileMetaData meta;
+  meta.oldest_ancester_time = kCurrentTime - 1023;
+  ASSERT_EQ(1, booster.GetBoostScore(&meta));
+}
+
 TEST_F(CompactionPickerTest, FileTtlBooster) {
   // Set TTL to 2048
   // TTL boosting for all levels starts at 1024,

db/compaction/file_pri.h

@@ -53,8 +53,10 @@ class FileTtlBooster {
       enabled_ = true;
       uint64_t all_boost_start_age = ttl / 2;
       uint64_t all_boost_age_range = (ttl / 32) * 31 - all_boost_start_age;
+      // TODO(cbi): more reasonable algorithm that gives different values
+      //   when num_non_empty_levels - level - 1 > 63.
       uint64_t boost_age_range =
-          all_boost_age_range >> (num_non_empty_levels - level - 1);
+          all_boost_age_range >> std::min(63, num_non_empty_levels - level - 1);
       boost_age_start_ = all_boost_start_age + boost_age_range;
       const uint64_t kBoostRatio = 16;
       // prevent 0 value to avoid divide 0 error.

unreleased_history/bug_fixes/shifting_componeng_too_large_file_ttl_booster.md

@@ -0,0 +1 @@
+Fix a bug in FileTTLBooster that can cause users with a large number of levels (more than 65) to see errors like "runtime error: shift exponent .. is too large.." (#11673).