Optimize memory footprint (#3376)

util/src/hashdb.rs

@@ -17,10 +17,10 @@
 //! Database of byte-slices keyed to their Keccak hash.
 use hash::*;
 use std::collections::HashMap;
-use elastic_array::ElasticArray256;
+use elastic_array::ElasticArray128;
 
 /// `HashDB` value type.
-pub type DBValue = ElasticArray256<u8>;
+pub type DBValue = ElasticArray128<u8>;
 
 /// Trait modelling datastore keyed by a 32-byte Keccak hash.
 pub trait HashDB: AsHashDB + Send + Sync {

util/src/kvdb.rs

@@ -464,6 +464,7 @@ impl Database {
 				try!(db.write_opt(batch, &self.write_opts));
 				for column in self.flushing.write().iter_mut() {
 					column.clear();
+					column.shrink_to_fit();
 				}
 				Ok(())
 			},