Allow manual compactions to run in parallel by default (#10317)

Summary:
This PR changes the default value of
`CompactRangeOptions::exclusive_manual_compaction` from true to false so
manual `CompactRange()`s can run in parallel with other compactions. I
believe no artificial parallelism restriction is the intuitive behavior
so feel the old default value is a trap, which I have fallen into
several times, including yesterday.
`CompactRangeOptions::exclusive_manual_compaction == false` has been
used in both our correctness test and in production for years so should
be reasonably safe.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10317

Reviewed By: jay-zhuang

Differential Revision: D37659392

Pulled By: ajkr

fbshipit-source-id: 504915e978bbe300b79483d064070c75e93d91e5

HISTORY.md

@@ -10,6 +10,7 @@
 
 ### Public API changes
 * Removed Customizable support for RateLimiter and removed its CreateFromString() and Type() functions.
+* `CompactRangeOptions::exclusive_manual_compaction` is now false by default. This ensures RocksDB does not introduce artificial parallelism limitations by default.
 
 ### Bug Fixes
 * Fix a bug where `GenericRateLimiter` could revert the bandwidth set dynamically using `SetBytesPerSecond()` when a user configures a structure enclosing it, e.g., using `GetOptionsFromString()` to configure an `Options` that references an existing `RateLimiter` object.

db/db_compaction_test.cc

@@ -2660,8 +2660,9 @@ TEST_F(DBCompactionTest, ManualAutoRace) {
   TEST_SYNC_POINT("DBCompactionTest::ManualAutoRace:1");
   // The auto compaction will wait until the manual compaction is registerd
   // before processing so that it will be cancelled.
-  ASSERT_OK(dbfull()->CompactRange(CompactRangeOptions(), handles_[1], nullptr,
+  CompactRangeOptions cro;
-                                   nullptr));
+  cro.exclusive_manual_compaction = true;
+  ASSERT_OK(dbfull()->CompactRange(cro, handles_[1], nullptr, nullptr));
   ASSERT_EQ("0,1", FilesPerLevel(1));
 
   // Eventually the cancelled compaction will be rescheduled and executed.

db/db_impl/db_impl_compaction_flush.cc

@@ -1853,8 +1853,7 @@ Status DBImpl::RunManualCompaction(
   // jobs drops to zero. This used to be needed to ensure that this manual
   // compaction can compact any range of keys/files. Now it is optional
   // (see `CompactRangeOptions::exclusive_manual_compaction`). The use case for
-  // `exclusive_manual_compaction=true` (the default) is unclear beyond not
+  // `exclusive_manual_compaction=true` is unclear beyond not trusting the code.
-  // trusting the new code.
   //
   // HasPendingManualCompaction() is true when at least one thread is inside
   // RunManualCompaction(), i.e. during that time no other compaction will

include/rocksdb/options.h

@@ -1843,8 +1843,11 @@ enum class BlobGarbageCollectionPolicy {
 // CompactRangeOptions is used by CompactRange() call.
 struct CompactRangeOptions {
   // If true, no other compaction will run at the same time as this
-  // manual compaction
+  // manual compaction.
-  bool exclusive_manual_compaction = true;
+  //
+  // Default: false
+  bool exclusive_manual_compaction = false;
+
   // If true, compacted files will be moved to the minimum level capable
   // of holding the data or given level (specified non-negative target_level).
   bool change_level = false;