Merge #10526: Force on-the-fly compaction during pertxout upgrade

efeb273 Force on-the-fly compaction during pertxout upgrade (Pieter Wuille)

Pull request description:

  It seems that LevelDB tends to leave the old "per txid" UTXO entries in the database lying around for a significant amount of time during and after the per-txout upgrade. This introduces a `CompactRange` function in the database wrapper, and invokes it after every batch of updates in `CCoinsViewDB::Upgrade()`. This lowers temporary disk usage during and after the upgrade.

Tree-SHA512: fbf964c0a33f4e73709c999c8a2bfdef974779c15820907398a2f8828f5fa3e4e153ddd9031d6fc5083be81e22b999b9bd826fd063ad8b88f55c5e8342503290

Author: laanwj

src/dbwrapper.h

@@ -321,6 +321,23 @@ class CDBWrapper
         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

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);
@@ -409,13 +410,16 @@ bool CCoinsViewDB::Upgrade() {
             if (batch.SizeEstimate() > batch_size) {
                 db.WriteBatch(batch);
                 batch.Clear();
+                db.CompactRange(prev_key, key);
+                prev_key = key;
             }
             pcursor->Next();
         } else {
             break;
         }
     }
     db.WriteBatch(batch);
+    db.CompactRange({DB_COINS, uint256()}, key);
     uiInterface.SetProgressBreakAction(std::function<void(void)>());
     LogPrintf("[%s].\n", ShutdownRequested() ? "CANCELLED" : "DONE");
     return true;