Fix bug that number of table loading threads is set as a boolean (#6576)

Summary:
When applying a new version in non DB open case, optimize_filters_for_hits is used for max_threads, which is clearly a bug. It is not clear what the indented value in the first place, but it value 1 makes sense here, which would create no extra threads. This bug is not expected to cause user visible problems, assuming C++ implicitly cast bool to 0 or 1.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6576

Test Plan: Run all exsiting test.

Reviewed By: ajkr

Differential Revision: D20602467

fbshipit-source-id: 40b2cd8619aba09ae9242b36c415464db3c9b737

HISTORY.md

@@ -6,6 +6,7 @@
 ### Bug Fixes
 * Fix a bug where range tombstone blocks in ingested files were cached incorrectly during ingestion. If range tombstones were read from those incorrectly cached blocks, the keys they covered would be exposed.
 * Fix a data race that might cause crash when calling DB::GetCreationTimeOfOldestFile() by a small chance. The bug was introduced in 6.6 Release.
+* Fix a bug where a boolean value optimize_filters_for_hits was for max threads when calling load table handles after a flush or compaction. The value is correct to 1. The bug should not cause user visible problems.
 
 ### Performance Improvements
 * In CompactRange, for levels starting from 0, if the level does not have any file with any key falling in the specified range, the level is skipped. So instead of always compacting from level 0, the compaction starts from the first level with keys in the specified range until the last such level.

db/version_set.cc

@@ -3811,7 +3811,7 @@ Status VersionSet::ProcessManifestWrites(
                builder_guards.size() == versions.size());
         ColumnFamilyData* cfd = versions[i]->cfd_;
         s = builder_guards[i]->version_builder()->LoadTableHandlers(
-            cfd->internal_stats(), cfd->ioptions()->optimize_filters_for_hits,
+            cfd->internal_stats(), 1 /* max_threads */,
             true /* prefetch_index_and_filter_in_cache */,
             false /* is_initial_load */,
             mutable_cf_options_ptrs[i]->prefix_extractor.get());