c abi: allow compaction filter ignore snapshot (facebook#1268)

close facebook#1262

db/c.cc

@@ -123,6 +123,7 @@ struct rocksdb_compactionfilter_t : public CompactionFilter {
       char** new_value, size_t *new_value_length,
       unsigned char* value_changed);
   const char* (*name_)(void*);
+  unsigned char ignore_snapshots_;
 
   virtual ~rocksdb_compactionfilter_t() {
     (*destructor_)(state_);
@@ -148,6 +149,8 @@ struct rocksdb_compactionfilter_t : public CompactionFilter {
   }
 
   virtual const char* Name() const override { return (*name_)(state_); }
+
+  virtual bool IgnoreSnapshots() const override { return ignore_snapshots_; }
 };
 
 struct rocksdb_compactionfilterfactory_t : public CompactionFilterFactory {
@@ -1919,10 +1922,17 @@ rocksdb_compactionfilter_t* rocksdb_compactionfilter_create(
   result->state_ = state;
   result->destructor_ = destructor;
   result->filter_ = filter;
+  result->ignore_snapshots_ = false;
   result->name_ = name;
   return result;
 }
 
+void rocksdb_compactionfilter_set_ignore_snapshots(
+  rocksdb_compactionfilter_t* filter,
+  unsigned char whether_ignore) {
+  filter->ignore_snapshots_ = whether_ignore;
+}
+
 void rocksdb_compactionfilter_destroy(rocksdb_compactionfilter_t* filter) {
   delete filter;
 }

include/rocksdb/c.h

@@ -729,6 +729,8 @@ rocksdb_compactionfilter_create(
                             size_t* new_value_length,
                             unsigned char* value_changed),
     const char* (*name)(void*));
+extern ROCKSDB_LIBRARY_API void rocksdb_compactionfilter_set_ignore_snapshots(
+    rocksdb_compactionfilter_t*, unsigned char);
 extern ROCKSDB_LIBRARY_API void rocksdb_compactionfilter_destroy(
     rocksdb_compactionfilter_t*);
 

include/rocksdb/compaction_filter.h

@@ -106,7 +106,7 @@ class CompactionFilter {
 
   // By default, compaction will only call Filter() on keys written after the
   // most recent call to GetSnapshot(). However, if the compaction filter
-  // overrides IgnoreSnapshots to make it return false, the compaction filter
+  // overrides IgnoreSnapshots to make it return true, the compaction filter
   // will be called even if the keys were written before the last snapshot.
   // This behavior is to be used only when we want to delete a set of keys
   // irrespective of snapshots. In particular, care should be taken