Add leveldb::Cache::Prune

Prune() drops on-memory read cache of the database, so that the client can
relief its memory shortage.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=101335710

1 files changed, 7 insertions, 0 deletions

diff --git a/include/leveldb/cache.h b/include/leveldb/cache.h
index 1a201e5..5f86cd0 100644
--- a/include/leveldb/cache.h
+++ b/include/leveldb/cache.h
@@ -81,6 +81,13 @@ class Cache {
   // its cache keys.
   virtual uint64_t NewId() = 0;
 
+  // Remove all cache entries that are not actively in use.  Memory-constrained
+  // applications may wish to call this method to reduce memory usage.
+  // Default implementation of Prune() does nothing.  Subclasses are strongly
+  // encouraged to override the default implementation.  A future release of
+  // leveldb may change Prune() to a pure abstract method.
+  virtual void Prune() {}
+
  private:
   void LRU_Remove(Handle* e);
   void LRU_Append(Handle* e);