DeleteRange interface

Summary:
Expose DeleteRange() interface since we think the implementation is functionally correct now.
Closes https://github.com/facebook/rocksdb/pull/1503

Differential Revision: D4171921

Pulled By: ajkr

fbshipit-source-id: 5e21c98

HISTORY.md

@@ -3,6 +3,7 @@
 ### Public API Change
 * Options::max_bytes_for_level_multiplier is now a double along with all getters and setters.
 * Support dynamically change `delayed_write_rate` and `max_total_wal_size` options via SetDBOptions().
+* Introduce DB::DeleteRange for optimized deletion of large ranges of contiguous keys.
 
 ### New Features
 * Add avoid_flush_during_shutdown option, which speeds up DB shutdown by not flushing unpersisted data (i.e. with disableWAL = true). Unpersisted data will be lost. The options is dynamically changeable via SetDBOptions().

db/db_impl.cc

@@ -5845,6 +5845,14 @@ Status DB::SingleDelete(const WriteOptions& opt,
   return Write(opt, &batch);
 }
 
+Status DB::DeleteRange(const WriteOptions& opt,
+                       ColumnFamilyHandle* column_family,
+                       const Slice& begin_key, const Slice& end_key) {
+  WriteBatch batch;
+  batch.DeleteRange(column_family, begin_key, end_key);
+  return Write(opt, &batch);
+}
+
 Status DB::Merge(const WriteOptions& opt, ColumnFamilyHandle* column_family,
                  const Slice& key, const Slice& value) {
   WriteBatch batch;

include/rocksdb/db.h

@@ -235,6 +235,25 @@ class DB {
     return SingleDelete(options, DefaultColumnFamily(), key);
   }
 
+  // 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
+  // ["begin_key", "end_key").
+  //
+  // This feature is currently an experimental performance optimization for
+  // deleting very large ranges of contiguous keys. Invoking it many times or on
+  // small ranges may severely degrade read performance; in particular, the
+  // resulting performance can be worse than calling Delete() for each key in
+  // the range. Note also the degraded read performance affects keys outside the
+  // deleted ranges, and affects database operations involving scans, like flush
+  // and compaction.
+  //
+  // Consider setting ReadOptions::ignore_range_deletions = true to speed
+  // up reads for key(s) that are known to be unaffected by range deletions.
+  virtual Status DeleteRange(const WriteOptions& options,
+                             ColumnFamilyHandle* column_family,
+                             const Slice& begin_key, const Slice& end_key);
+
   // Merge the database entry for "key" with "value".  Returns OK on success,
   // and a non-OK status on error. The semantics of this operation is
   // determined by the user provided merge_operator when opening DB.