add block header cache to store (#996)

* WIP - add blocks header cache to store
The DifficultyIter is expensive to use when validating block headers.

* lru_cache

* rustfmt

* cleanup

Cargo.lock

@@ -663,6 +663,7 @@ dependencies = [
  "grin_pow 0.2.0",
  "grin_store 0.2.0",
  "grin_util 0.2.0",
+ "lru-cache 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1064,6 +1065,11 @@ dependencies = [
  "vcpkg 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "linked-hash-map"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "log"
 version = "0.3.9"
@@ -1080,6 +1086,14 @@ dependencies = [
  "cfg-if 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "lru-cache"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "linked-hash-map 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "make-cmd"
 version = "0.1.0"
@@ -2445,8 +2459,10 @@ dependencies = [
 "checksum libloading 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "fd38073de8f7965d0c17d30546d4bb6da311ab428d1c7a3fc71dff7f9d4979b9"
 "checksum librocksdb-sys 5.11.3 (registry+https://github.com/rust-lang/crates.io-index)" = "1b0fa7f4ca5ceff76237db63802cb073d84e64a327e38478e79a669093fb7fa5"
 "checksum libz-sys 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)" = "87f737ad6cc6fd6eefe3d9dc5412f1573865bded441300904d2f42269e140f16"
+"checksum linked-hash-map 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7860ec297f7008ff7a1e3382d7f7e1dcd69efc94751a2284bafc3d013c2aa939"
 "checksum log 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "e19e8d5c34a3e0e2223db8e060f9e8264aeeb5c5fc64a4ee9965c062211c024b"
 "checksum log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "89f010e843f2b1a31dbd316b3b8d443758bc634bed37aabade59c686d644e0a2"
+"checksum lru-cache 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "4d06ff7ff06f729ce5f4e227876cb88d10bc59cd4ae1e09fbb2bde15c850dc21"
 "checksum make-cmd 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a8ca8afbe8af1785e09636acb5a41e08a765f5f0340568716c18a8700ba3c0d3"
 "checksum maplit 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "08cbb6b4fef96b6d77bfc40ec491b1690c779e77b05cd9f07f787ed376fd4c43"
 "checksum matches 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "100aabe6b8ff4e4a7e32c1c13523379802df0772b82466207ac25b013f193376"

chain/Cargo.toml

@@ -12,6 +12,7 @@ slog = { version = "~2.1", features = ["max_level_trace", "release_max_level_tra
 serde = "1"
 serde_derive = "1"
 time = "0.1"
+lru-cache = "0.1"
 
 grin_core = { path = "../core" }
 grin_keychain = { path = "../keychain" }

chain/src/lib.rs

@@ -23,6 +23,7 @@
 #[macro_use]
 extern crate bitflags;
 extern crate byteorder;
+extern crate lru_cache;
 extern crate serde;
 #[macro_use]
 extern crate serde_derive;

chain/src/store.rs

@@ -14,7 +14,9 @@
 
 //! Implements storage primitives required by the chain
 
-use std::sync::Arc;
+use std::sync::{Arc, RwLock};
+
+use lru_cache::LruCache;
 
 use util::secp::pedersen::Commitment;
 
@@ -24,6 +26,7 @@ use core::core::{Block, BlockHeader};
 use core::consensus::TargetError;
 use core::core::target::Difficulty;
 use grin_store::{self, option_to_not_found, to_key, Error, u64_to_key};
+use util::LOGGER;
 
 const STORE_SUBPATH: &'static str = "chain";
 
@@ -41,13 +44,17 @@ const BLOCK_PMMR_FILE_METADATA_PREFIX: u8 = 'p' as u8;
 /// store.
 pub struct ChainKVStore {
 	db: grin_store::Store,
+	header_cache: Arc<RwLock<LruCache<Hash, BlockHeader>>>,
 }
 
 impl ChainKVStore {
 	/// Create new chain store
 	pub fn new(root_path: String) -> Result<ChainKVStore, Error> {
 		let db = grin_store::Store::open(format!("{}/{}", root_path, STORE_SUBPATH).as_str())?;
-		Ok(ChainKVStore { db: db })
+		Ok(ChainKVStore {
+			db,
+			header_cache: Arc::new(RwLock::new(LruCache::new(100))),
+		})
 	}
 }
 
@@ -113,10 +120,30 @@ impl ChainStore for ChainKVStore {
 	}
 
 	fn get_block_header(&self, h: &Hash) -> Result<BlockHeader, Error> {
-		option_to_not_found(
+		{
+			let mut header_cache = self.header_cache.write().unwrap();
+
+			// cache hit - return the value from the cache
+			if let Some(header) = header_cache.get_mut(h) {
+				return Ok(header.clone());
+			}
+		}
+
+		let header: Result<BlockHeader, Error> = option_to_not_found(
 			self.db
 				.get_ser(&to_key(BLOCK_HEADER_PREFIX, &mut h.to_vec())),
-		)
+		);
+
+		// cache miss - so adding to the cache for next time
+		if let Ok(header) = header {
+			{
+				let mut header_cache = self.header_cache.write().unwrap();
+				header_cache.insert(*h, header.clone());
+			}
+			Ok(header)
+		} else {
+			header
+		}
 	}
 
 	/// Save the block and its header