Replace GetUserKey with ExtractUserKey (#9664)

Summary:
Replace `GetUserKey` with `ExtractUserKey`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9664

Reviewed By: jay-zhuang

Differential Revision: D34673571

Pulled By: ajkr

fbshipit-source-id: 5acf7d0d1a45efce0ccbe505991acf76c9cdc461

table/plain/plain_table_builder.h

@@ -122,17 +122,13 @@ class PlainTableBuilder: public TableBuilder {
 
   Slice GetPrefix(const Slice& target) const {
     assert(target.size() >= 8);  // target is internal key
-    return GetPrefixFromUserKey(GetUserKey(target));
+    return GetPrefixFromUserKey(ExtractUserKey(target));
   }
 
   Slice GetPrefix(const ParsedInternalKey& target) const {
     return GetPrefixFromUserKey(target.user_key);
   }
 
-  Slice GetUserKey(const Slice& key) const {
-    return Slice(key.data(), key.size() - 8);
-  }
-
   Slice GetPrefixFromUserKey(const Slice& user_key) const {
     if (!IsTotalOrderMode()) {
       return prefix_extractor_->Transform(user_key);

table/plain/plain_table_reader.cc

@@ -563,7 +563,7 @@ Status PlainTableReader::Get(const ReadOptions& /*ro*/, const Slice& target,
           Status::InvalidArgument("Get() is not allowed in full scan mode.");
     }
     // Match whole user key for bloom filter check.
-    if (!MatchBloom(GetSliceHash(GetUserKey(target)))) {
+    if (!MatchBloom(GetSliceHash(ExtractUserKey(target)))) {
       return Status::OK();
     }
     // in total order mode, there is only one bucket 0, and we always use empty

table/plain/plain_table_reader.h

@@ -179,17 +179,13 @@ class PlainTableReader: public TableReader {
 
   Slice GetPrefix(const Slice& target) const {
     assert(target.size() >= 8);  // target is internal key
-    return GetPrefixFromUserKey(GetUserKey(target));
+    return GetPrefixFromUserKey(ExtractUserKey(target));
   }
 
   Slice GetPrefix(const ParsedInternalKey& target) const {
     return GetPrefixFromUserKey(target.user_key);
   }
 
-  Slice GetUserKey(const Slice& key) const {
-    return Slice(key.data(), key.size() - 8);
-  }
-
   Slice GetPrefixFromUserKey(const Slice& user_key) const {
     if (!IsTotalOrderMode()) {
       return prefix_extractor_->Transform(user_key);