validate range tombstone covers positive range (#6788)

Summary:
We found some files containing nothing but negative range tombstones,
and unsurprisingly their metadata specified a negative range, which made
things crash. Time to add a bit of user input validation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6788

Reviewed By: zhichao-cao

Differential Revision: D21343719

Pulled By: ajkr

fbshipit-source-id: f1c16e4c3e9fa150958c8c866176632a3206fb74

HISTORY.md

@@ -22,6 +22,7 @@
 * Add a ConfigOptions argument to the APIs dealing with converting options to and from strings and files.  The ConfigOptions is meant to replace some of the options (such as input_strings_escaped and ignore_unknown_options) and allow for more parameters to be passed in the future without changing the function signature.
 * Add NewFileChecksumGenCrc32cFactory to the file checksum public API, such that the builtin Crc32c based file checksum generator factory can be used by applications.
 * Add IsDirectory to Env and FS to indicate if a path is a directory.
+* DeleteRange now returns `Status::InvalidArgument` if the range's end key comes before its start key according to the user comparator. Previously the behavior was undefined.
 
 ### New Features
 * Added support for pipelined & parallel compression optimization for `BlockBasedTableBuilder`. This optimization makes block building, block compression and block appending a pipeline, and uses multiple threads to accelerate block compression. Users can set `CompressionOptions::parallel_threads` greater than 1 to enable compression parallelism. This feature is experimental for now.

db/db_range_del_test.cc

@@ -47,6 +47,21 @@ TEST_F(DBRangeDelTest, WriteBatchWithIndexNotSupported) {
   ASSERT_TRUE(indexedBatch.DeleteRange("dr1", "dr1").IsNotSupported());
 }
 
+TEST_F(DBRangeDelTest, EndSameAsStartCoversNothing) {
+  ASSERT_OK(db_->Put(WriteOptions(), "b", "val"));
+  ASSERT_OK(
+      db_->DeleteRange(WriteOptions(), db_->DefaultColumnFamily(), "b", "b"));
+  ASSERT_EQ("val", Get("b"));
+}
+
+TEST_F(DBRangeDelTest, EndComesBeforeStartInvalidArgument) {
+  db_->Put(WriteOptions(), "b", "val");
+  ASSERT_TRUE(
+      db_->DeleteRange(WriteOptions(), db_->DefaultColumnFamily(), "b", "a")
+          .IsInvalidArgument());
+  ASSERT_EQ("val", Get("b"));
+}
+
 TEST_F(DBRangeDelTest, FlushOutputHasOnlyRangeTombstones) {
   do {
     DestroyAndReopen(CurrentOptions());

db/write_batch.cc

@@ -1630,6 +1630,15 @@ class MemTableInserter : public WriteBatch::Handler {
             cfd->ioptions()->table_factory->Name() + " in CF " +
             cfd->GetName());
       }
+      int cmp = cfd->user_comparator()->Compare(begin_key, end_key);
+      if (cmp > 0) {
+        // It's an empty range where endpoints appear mistaken. Don't bother
+        // applying it to the DB, and return an error to the user.
+        return Status::InvalidArgument("end key comes before start key");
+      } else if (cmp == 0) {
+        // It's an empty range. Don't bother applying it to the DB.
+        return Status::OK();
+      }
     }
 
     auto ret_status =

include/rocksdb/db.h

@@ -356,8 +356,11 @@ class DB {
 
   // Removes the database entries in the range ["begin_key", "end_key"), i.e.,
   // including "begin_key" and excluding "end_key". Returns OK on success, and
-  // a non-OK status on error. It is not an error if no keys exist in the range
+  // a non-OK status on error. It is not an error if the database does not
-  // ["begin_key", "end_key").
+  // contain any existing data in the range ["begin_key", "end_key").
+  //
+  // If "end_key" comes before "start_key" according to the user's comparator,
+  // a `Status::InvalidArgument` is returned.
   //
   // This feature is now usable in production, with the following caveats:
   // 1) Accumulating many range tombstones in the memtable will degrade read