coins: add Sync() method to allow flush without cacheCoins drop

In certain circumstances, we may want to flush to disk without
emptying `cacheCoins`, which affects performance. UTXO snapshot
activation is one such case.

This method is currently unused and this commit does not
change any behavior.

Incorporates feedback from John Newbery.

Co-authored-by: Suhas Daftuar <sdaftuar@gmail.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/src/txdb.cpp b/src/txdb.cpp
index f04a4e9800..c12b540b9b 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -111,7 +111,7 @@ std::vector<uint256> CCoinsViewDB::GetHeadBlocks() const {
     return vhashHeadBlocks;
 }
 
-bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
+bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, bool erase) {
     CDBBatch batch(*m_db);
     size_t count = 0;
     size_t changed = 0;
@@ -146,8 +146,7 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
             changed++;
         }
         count++;
-        CCoinsMap::iterator itOld = it++;
-        mapCoins.erase(itOld);
+        it = erase ? mapCoins.erase(it) : std::next(it);
         if (batch.SizeEstimate() > batch_size) {
             LogPrint(BCLog::COINDB, "Writing partial batch of %.2f MiB\n", batch.SizeEstimate() * (1.0 / 1048576.0));
             m_db->WriteBatch(batch);