From efeb273305e3e4d2c42e1e153de83c1cb6f0a28c Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Fri, 2 Jun 2017 17:52:37 -0700
Subject: [PATCH] Force on-the-fly compaction during pertxout upgrade

---
 src/dbwrapper.h | 17 +++++++++++++++++
 src/txdb.cpp    |  6 +++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/dbwrapper.h b/src/dbwrapper.h
index 24ef71bfbf..d36188652a 100644
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -321,6 +321,23 @@ public:
         pdb->GetApproximateSizes(&range, 1, &size);
         return size;
     }
+
+    /**
+     * Compact a certain range of keys in the database.
+     */
+    template<typename K>
+    void CompactRange(const K& key_begin, const K& key_end) const
+    {
+        CDataStream ssKey1(SER_DISK, CLIENT_VERSION), ssKey2(SER_DISK, CLIENT_VERSION);
+        ssKey1.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
+        ssKey2.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
+        ssKey1 << key_begin;
+        ssKey2 << key_end;
+        leveldb::Slice slKey1(ssKey1.data(), ssKey1.size());
+        leveldb::Slice slKey2(ssKey2.data(), ssKey2.size());
+        pdb->CompactRange(&slKey1, &slKey2);
+    }
+
 };
 
 #endif // BITCOIN_DBWRAPPER_H
diff --git a/src/txdb.cpp b/src/txdb.cpp
index aa0b73a417..fd730c368a 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -375,12 +375,13 @@ bool CCoinsViewDB::Upgrade() {
     CDBBatch batch(db);
     uiInterface.SetProgressBreakAction(StartShutdown);
     int reportDone = 0;
+    std::pair<unsigned char, uint256> key;
+    std::pair<unsigned char, uint256> prev_key = {DB_COINS, uint256()};
     while (pcursor->Valid()) {
         boost::this_thread::interruption_point();
         if (ShutdownRequested()) {
             break;
         }
-        std::pair<unsigned char, uint256> key;
         if (pcursor->GetKey(key) && key.first == DB_COINS) {
             if (count++ % 256 == 0) {
                 uint32_t high = 0x100 * *key.second.begin() + *(key.second.begin() + 1);
@@ -409,6 +410,8 @@ bool CCoinsViewDB::Upgrade() {
             if (batch.SizeEstimate() > batch_size) {
                 db.WriteBatch(batch);
                 batch.Clear();
+                db.CompactRange(prev_key, key);
+                prev_key = key;
             }
             pcursor->Next();
         } else {
@@ -416,6 +419,7 @@ bool CCoinsViewDB::Upgrade() {
         }
     }
     db.WriteBatch(batch);
+    db.CompactRange({DB_COINS, uint256()}, key);
     uiInterface.SetProgressBreakAction(std::function<void(void)>());
     LogPrintf("[%s].\n", ShutdownRequested() ? "CANCELLED" : "DONE");
     return true;