Improve FullFilterBitsReader::HashMayMatch's doc (#4202)

Summary:
HashMayMatch is related to AddKey() instead of CreateFilter().
Also applies some minor Fixes #4191 #4200 #3910
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4202

Differential Revision: D9180945

Pulled By: maysamyabandeh

fbshipit-source-id: 6f07b81c5bb9bda5c0273475b486ba8a030471e6

db/db_impl_write.cc

@@ -573,7 +573,6 @@ Status DBImpl::WriteImplWALOnly(const WriteOptions& write_options,
   }
   // else we are the leader of the write batch group
   assert(w.state == WriteThread::STATE_GROUP_LEADER);
-  WriteContext write_context;
   WriteThread::WriteGroup write_group;
   uint64_t last_sequence;
   nonmem_write_thread_.EnterAsBatchGroupLeader(&w, &write_group);

util/bloom.cc

@@ -199,10 +199,10 @@ class FullFilterBitsReader : public FilterBitsReader {
                              uint32_t* num_lines);
 
   // "filter" contains the data appended by a preceding call to
-  // CreateFilterFromHash() on this class.  This method must return true if
+  // FilterBitsBuilder::Finish. This method must return true if the key was
-  // the key was in the list of keys passed to CreateFilter().
+  // passed to FilterBitsBuilder::AddKey. This method may return true or false
-  // This method may return true or false if the key was not on the
+  // if the key was not on the list, but it should aim to return false with a
-  // list, but it should aim to return false with a high probability.
+  // high probability.
   //
   // hash: target to be checked
   // filter: the whole filter, including meta data bytes

utilities/backupable/backupable_db.cc

@@ -1754,7 +1754,7 @@ Status BackupEngineImpl::BackupMeta::StoreToFile(bool sync) {
     std::string hex_encoded_metadata =
         Slice(app_metadata_).ToString(/* hex */ true);
 
-    // +1 to accomodate newline character
+    // +1 to accommodate newline character
     size_t hex_meta_strlen = kMetaDataPrefix.ToString().length() + hex_encoded_metadata.length() + 1;
     if (hex_meta_strlen >= buf_size) {
       return Status::Corruption("Buffer too small to fit backup metadata");

utilities/persistent_cache/block_cache_tier.cc

@@ -163,7 +163,7 @@ PersistentCache::StatsType BlockCacheTier::Stats() {
       stats_.read_hit_latency_.Average());
   Add(&stats, "persistentcache.blockcachetier.read_miss_latency",
       stats_.read_miss_latency_.Average());
-  Add(&stats, "persistenetcache.blockcachetier.write_latency",
+  Add(&stats, "persistentcache.blockcachetier.write_latency",
       stats_.write_latency_.Average());
 
   auto out = PersistentCacheTier::Stats();