Do not keep fully spent but unwritten CCoins entries cached.

Instead of storing CCoins entries directly in CCoinsMap, store a CCoinsCacheEntry
which additionally keeps track of whether a particular entry is:
* dirty: potentially different from its parent view.
* fresh: the parent view is known to not have a non-pruned version.

This allows us to skip non-dirty cache entries when pushing batches of changes up,
and to remove CCoins entries about transactions that are fully spent before the
parent cache learns about them.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/txdb.cpp b/src/txdb.cpp
index 3b353ab624..89830ced73 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -45,17 +45,22 @@ uint256 CCoinsViewDB::GetBestBlock() const {
 }
 
 bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
-    LogPrint("coindb", "Committing %u changed transactions to coin database...\n", (unsigned int)mapCoins.size());
-
     CLevelDBBatch batch;
+    size_t count = 0;
+    size_t changed = 0;
     for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
-        BatchWriteCoins(batch, it->first, it->second);
+        if (it->second.flags & CCoinsCacheEntry::DIRTY) {
+            BatchWriteCoins(batch, it->first, it->second.coins);
+            changed++;
+        }
+        count++;
         CCoinsMap::iterator itOld = it++;
         mapCoins.erase(itOld);
     }
     if (hashBlock != uint256(0))
         BatchWriteHashBestChain(batch, hashBlock);
 
+    LogPrint("coindb", "Committing %u changed transactions (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
     return db.WriteBatch(batch);
 }