Merge bitcoin/bitcoin#25957: wallet: fast rescan with BIP157 block filters for descriptor wallets

0582932260e7de4e8aba01d63e7c8a9ddb9c3685 test: add test for fast rescan using block filters (top-up detection) (Sebastian Falbesoner)
ca48a4694f73e5be8f971ae482ebc2cce4caef44 rpc: doc: mention rescan speedup using `blockfilterindex=1` in affected wallet RPCs (Sebastian Falbesoner)
3449880b499d54bfbcf6caeed52851ce55259ed7 wallet: fast rescan: show log message for every non-skipped block (Sebastian Falbesoner)
935c6c4b234bbb0565cda6f58ee298048856acae wallet: take use of `FastWalletRescanFilter` (Sebastian Falbesoner)
70b35139040a2351c845a1cec1dafd2fbcd16e93 wallet: add `FastWalletRescanFilter` class for speeding up rescans (Sebastian Falbesoner)
c051026586fb269584bcba41de8a4a90280f5a7e wallet: add method for retrieving the end range for a ScriptPubKeyMan (Sebastian Falbesoner)
845279132b494f03b84d689c666fdcfad37f5a42 wallet: support fetching scriptPubKeys with minimum descriptor range index (Sebastian Falbesoner)
088e38d3bbea9694b319bc34e0d2e70d210c38b4 add chain interface methods for using BIP 157 block filters (Sebastian Falbesoner)

Pull request description:

  ## Description

  This PR is another take of using BIP 157 block filters (enabled by `-blockfilterindex=1`) for faster wallet rescans and is a modern revival of #15845. For reviewers new to this topic I can highly recommend to read the corresponding PR review club (https://bitcoincore.reviews/15845).

  The basic idea is to skip blocks for deeper inspection (i.e. looking at every single tx for matches) if our block filter doesn't match any of the block's spent or created UTXOs are relevant for our wallet. Note that there can be false-positives (see https://bitcoincore.reviews/15845#l-199 for a PR review club discussion about false-positive rates), but no false-negatives, i.e. it is safe to skip blocks if the filter doesn't match; if the filter *does* match even though there are no wallet-relevant txs in the block, no harm is done, only a little more time is spent extra.

  In contrast to #15845, this solution only supports descriptor wallets, which are way more widespread now than back in the time >3 years ago. With that approach, we don't have to ever derive the relevant scriptPubKeys ourselves from keys before populating the filter, and can instead shift the full responsibility to that to the `DescriptorScriptPubKeyMan` which already takes care of that automatically. Compared to legacy wallets, the `IsMine` logic for descriptor wallets is as trivial as checking if a scriptPubKey is included in the ScriptPubKeyMan's set of scriptPubKeys (`m_map_script_pub_keys`): https://github.com/bitcoin/bitcoin/blob/e191fac4f3c37820f0618f72f0a8e8b524531ab8/src/wallet/scriptpubkeyman.cpp#L1703-L1710

  One of the unaddressed issues of #15845 was that [the filter was only created once outside the loop](https://github.com/bitcoin/bitcoin/pull/15845#discussion_r343265997) and as such didn't take into account possible top-ups that have happened. This is solved here by keeping a state of ranged `DescriptorScriptPubKeyMan`'s descriptor end ranges and check at each iteration whether that range has increased since last time. If yes, we update the filter with all scriptPubKeys that have been added since the last filter update with a range index equal or higher than the last end range. Note that finding new scriptPubKeys could be made more efficient than linearly iterating through the whole `m_script_pub_keys` map (e.g. by introducing a bidirectional map), but this would mean introducing additional complexity and state and it's probably not worth it at this time, considering that the performance gain is already significant.

  Output scripts from non-ranged `DescriptorScriptPubKeyMan`s (i.e. ones with a fixed set of output scripts that is never extended) are added only once when the filter is created first.

  ## Benchmark results

  Obviously, the speed-up indirectly correlates with the wallet tx frequency in the scanned range: the more blocks contain wallet-related transactions, the less blocks can be skipped due to block filter detection.

  In a [simple benchmark](https://github.com/theStack/bitcoin/blob/fast_rescan_functional_test_benchmark/test/functional/pr25957_benchmark.py), a regtest chain with 1008 blocks (corresponding to 1 week) is mined with 20000 scriptPubKeys contained (25 txs * 800 outputs) each. The blocks each have a weight of ~2500000 WUs and hence are about 62.5% full. A global constant `WALLET_TX_BLOCK_FREQUENCY` defines how often wallet-related txs are included in a block. The created descriptor wallet (default setting of `keypool=1000`, we have 8*1000 = 8000 scriptPubKeys at the start) is backuped via the `backupwallet` RPC before the mining starts and imported via `restorewallet` RPC after. The measured time for taking this import process (which involves a rescan) once with block filters (`-blockfilterindex=1`) and once without block filters (`-blockfilterindex=0`) yield the relevant result numbers for the benchmark.

  The following table lists the results, sorted from worst-case (all blocks contain wallte-relevant txs, 0% can be skipped) to best-case (no blocks contain walltet-relevant txs, 100% can be skipped) where the frequencies have been picked arbitrarily:

  wallet-related tx frequency; 1 tx per...    | ratio of irrelevant blocks  | w/o filters | with filters | speed gain
  --------------------------------------------|-----------------------------|-------------|--------------|-------------
  ~ 10 minutes (every block)                  |              0%             |   56.806s   |   63.554s    |  ~0.9x
  ~ 20 minutes (every 2nd block)              |           50% (1/2)         |   58.896s   |   36.076s    |  ~1.6x
  ~ 30 minutes (every 3rd block)              |          66.67% (2/3)       |   56.781s   |   25.430s    |  ~2.2x
  ~ 1 hour (every 6th block)                  |          83.33% (5/6)       |   58.193s   |   15.786s    |  ~3.7x
  ~ 6 hours (every 36th block)                |          97.22% (35/36)     |   57.500s   |    6.935s    |  ~8.3x
  ~ 1 day (every 144th block)                 |         99.31% (143/144)    |   68.881s   |    6.107s    | ~11.3x
    (no txs)                                  |              100%           |   58.529s   |    5.630s    | ~10.4x

  Since even the (rather unrealistic) worst-case scenario of having wallet-related txs in _every_ block of the rescan range obviously doesn't take significantly longer, I'd argue it's reasonable to always take advantage of block filters if they are available and there's no need to provide an option for the user.

  Feedback about the general approach (but also about details like naming, where I struggled a lot) would be greatly appreciated. Thanks fly out to furszy for discussing this subject and patiently answering basic question about descriptor wallets!

ACKs for top commit:
  achow101:
    ACK 0582932260e7de4e8aba01d63e7c8a9ddb9c3685
  Sjors:
    re-utACK 0582932260e7de4e8aba01d63e7c8a9ddb9c3685
  aureleoules:
    ACK 0582932260e7de4e8aba01d63e7c8a9ddb9c3685 - minor changes, documentation and updated test since last review
  w0xlt:
    re-ACK https://github.com/bitcoin/bitcoin/pull/25957/commits/0582932260e7de4e8aba01d63e7c8a9ddb9c3685

Tree-SHA512: 3289ba6e4572726e915d19f3e8b251d12a4cec8c96d041589956c484b5575e3708b14f6e1e121b05fe98aff1c8724de4564a5a9123f876967d33343cbef242e1

9 files changed, 161 insertions, 34 deletions

diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
index 5fc0e540a9..7a3d88b18f 100644
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_INTERFACES_CHAIN_H
 #define BITCOIN_INTERFACES_CHAIN_H
 
+#include <blockfilter.h>
 #include <primitives/transaction.h> // For CTransactionRef
 #include <util/settings.h>          // For util::SettingsValue
 
@@ -143,6 +144,13 @@ public:
     //! or one of its ancestors.
     virtual std::optional<int> findLocatorFork(const CBlockLocator& locator) = 0;
 
+    //! Returns whether a block filter index is available.
+    virtual bool hasBlockFilterIndex(BlockFilterType filter_type) = 0;
+
+    //! Returns whether any of the elements match the block via a BIP 157 block filter
+    //! or std::nullopt if the block filter for this block couldn't be found.
+    virtual std::optional<bool> blockFilterMatchesAny(BlockFilterType filter_type, const uint256& block_hash, const GCSFilter::ElementSet& filter_set) = 0;
+
     //! Return whether node has the block and optionally return block metadata
     //! or contents.
     virtual bool findBlock(const uint256& hash, const FoundBlock& block={}) = 0;
diff --git a/src/logging.cpp b/src/logging.cpp
index c95c0b7e37..ed0c2a56a5 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -181,6 +181,7 @@ const CLogCategoryDesc LogCategories[] =
     {BCLog::UTIL, "util"},
     {BCLog::BLOCKSTORE, "blockstorage"},
     {BCLog::TXRECONCILIATION, "txreconciliation"},
+    {BCLog::SCAN, "scan"},
     {BCLog::ALL, "1"},
     {BCLog::ALL, "all"},
 };
@@ -283,6 +284,8 @@ std::string LogCategoryToStr(BCLog::LogFlags category)
         return "blockstorage";
     case BCLog::LogFlags::TXRECONCILIATION:
         return "txreconciliation";
+    case BCLog::LogFlags::SCAN:
+        return "scan";
     case BCLog::LogFlags::ALL:
         return "all";
     }
diff --git a/src/logging.h b/src/logging.h
index 5ee6665c76..14a0f08f8d 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -67,6 +67,7 @@ namespace BCLog {
         UTIL        = (1 << 25),
         BLOCKSTORE  = (1 << 26),
         TXRECONCILIATION = (1 << 27),
+        SCAN        = (1 << 28),
         ALL         = ~(uint32_t)0,
     };
     enum class Level {
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 8a0011a629..979c625463 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -4,10 +4,12 @@
 
 #include <addrdb.h>
 #include <banman.h>
+#include <blockfilter.h>
 #include <chain.h>
 #include <chainparams.h>
 #include <deploymentstatus.h>
 #include <external_signer.h>
+#include <index/blockfilterindex.h>
 #include <init.h>
 #include <interfaces/chain.h>
 #include <interfaces/handler.h>
@@ -536,6 +538,20 @@ public:
         }
         return std::nullopt;
     }
+    bool hasBlockFilterIndex(BlockFilterType filter_type) override
+    {
+        return GetBlockFilterIndex(filter_type) != nullptr;
+    }
+    std::optional<bool> blockFilterMatchesAny(BlockFilterType filter_type, const uint256& block_hash, const GCSFilter::ElementSet& filter_set) override
+    {
+        const BlockFilterIndex* block_filter_index{GetBlockFilterIndex(filter_type)};
+        if (!block_filter_index) return std::nullopt;
+
+        BlockFilter filter;
+        const CBlockIndex* index{WITH_LOCK(::cs_main, return chainman().m_blockman.LookupBlockIndex(block_hash))};
+        if (index == nullptr || !block_filter_index->LookupFilter(index, filter)) return std::nullopt;
+        return filter.GetFilter().MatchAny(filter_set);
+    }
     bool findBlock(const uint256& hash, const FoundBlock& block) override
     {
         WAIT_LOCK(cs_main, lock);
diff --git a/src/wallet/rpc/backup.cpp b/src/wallet/rpc/backup.cpp
index 1206a428fc..1d2d7d2a10 100644
--- a/src/wallet/rpc/backup.cpp
+++ b/src/wallet/rpc/backup.cpp
@@ -1589,7 +1589,8 @@ RPCHelpMan importdescriptors()
     return RPCHelpMan{"importdescriptors",
                 "\nImport descriptors. This will trigger a rescan of the blockchain based on the earliest timestamp of all descriptors being imported. Requires a new wallet backup.\n"
             "\nNote: This call can take over an hour to complete if using an early timestamp; during that time, other rpc calls\n"
-            "may report that the imported keys, addresses or scripts exist but related transactions are still missing.\n",
+            "may report that the imported keys, addresses or scripts exist but related transactions are still missing.\n"
+            "The rescan is significantly faster if block filters are available (using startup option \"-blockfilterindex=1\").\n",
                 {
                     {"requests", RPCArg::Type::ARR, RPCArg::Optional::NO, "Data to be imported",
                         {
@@ -1887,7 +1888,9 @@ RPCHelpMan restorewallet()
 {
     return RPCHelpMan{
         "restorewallet",
-        "\nRestore and loads a wallet from backup.\n",
+        "\nRestore and loads a wallet from backup.\n"
+        "\nThe rescan is significantly faster if a descriptor wallet is restored"
+        "\nand block filters are available (using startup option \"-blockfilterindex=1\").\n",
         {
             {"wallet_name", RPCArg::Type::STR, RPCArg::Optional::NO, "The name that will be applied to the restored wallet"},
             {"backup_file", RPCArg::Type::STR, RPCArg::Optional::NO, "The backup file that will be used to restore the wallet."},
diff --git a/src/wallet/rpc/transactions.cpp b/src/wallet/rpc/transactions.cpp
index 0e13e4756b..0fe4ed703d 100644
--- a/src/wallet/rpc/transactions.cpp
+++ b/src/wallet/rpc/transactions.cpp
@@ -839,7 +839,9 @@ RPCHelpMan rescanblockchain()
 {
     return RPCHelpMan{"rescanblockchain",
                 "\nRescan the local blockchain for wallet related transactions.\n"
-                "Note: Use \"getwalletinfo\" to query the scanning progress.\n",
+                "Note: Use \"getwalletinfo\" to query the scanning progress.\n"
+                "The rescan is significantly faster when used on a descriptor wallet\n"
+                "and block filters are available (using startup option \"-blockfilterindex=1\").\n",
                 {
                     {"start_height", RPCArg::Type::NUM, RPCArg::Default{0}, "block height where the rescan should start"},
                     {"stop_height", RPCArg::Type::NUM, RPCArg::Optional::OMITTED_NAMED_ARG, "the last block height that should be scanned. If none is provided it will rescan up to the tip at return time of this call."},
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 39afb79600..4c534d64ec 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -2645,16 +2645,26 @@ const WalletDescriptor DescriptorScriptPubKeyMan::GetWalletDescriptor() const
 
 const std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys() const
 {
+    return GetScriptPubKeys(0);
+}
+
+const std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys(int32_t minimum_index) const
+{
     LOCK(cs_desc_man);
     std::unordered_set<CScript, SaltedSipHasher> script_pub_keys;
     script_pub_keys.reserve(m_map_script_pub_keys.size());
 
-    for (auto const& script_pub_key: m_map_script_pub_keys) {
-        script_pub_keys.insert(script_pub_key.first);
+    for (auto const& [script_pub_key, index] : m_map_script_pub_keys) {
+        if (index >= minimum_index) script_pub_keys.insert(script_pub_key);
     }
     return script_pub_keys;
 }
 
+int32_t DescriptorScriptPubKeyMan::GetEndRange() const
+{
+    return m_max_cached_index + 1;
+}
+
 bool DescriptorScriptPubKeyMan::GetDescriptorString(std::string& out, const bool priv) const
 {
     LOCK(cs_desc_man);
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index 3ab489c374..eb77015956 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -643,6 +643,8 @@ public:
 
     const WalletDescriptor GetWalletDescriptor() const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
     const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const override;
+    const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys(int32_t minimum_index) const;
+    int32_t GetEndRange() const;
 
     bool GetDescriptorString(std::string& out, const bool priv) const;
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index e2c8f6eda3..431e970edc 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -5,6 +5,7 @@
 
 #include <wallet/wallet.h>
 
+#include <blockfilter.h>
 #include <chain.h>
 #include <consensus/amount.h>
 #include <consensus/consensus.h>
@@ -261,6 +262,64 @@ std::shared_ptr<CWallet> LoadWalletInternal(WalletContext& context, const std::s
         return nullptr;
     }
 }
+
+class FastWalletRescanFilter
+{
+public:
+    FastWalletRescanFilter(const CWallet& wallet) : m_wallet(wallet)
+    {
+        // fast rescanning via block filters is only supported by descriptor wallets right now
+        assert(!m_wallet.IsLegacy());
+
+        // create initial filter with scripts from all ScriptPubKeyMans
+        for (auto spkm : m_wallet.GetAllScriptPubKeyMans()) {
+            auto desc_spkm{dynamic_cast<DescriptorScriptPubKeyMan*>(spkm)};
+            assert(desc_spkm != nullptr);
+            AddScriptPubKeys(desc_spkm);
+            // save each range descriptor's end for possible future filter updates
+            if (desc_spkm->IsHDEnabled()) {
+                m_last_range_ends.emplace(desc_spkm->GetID(), desc_spkm->GetEndRange());
+            }
+        }
+    }
+
+    void UpdateIfNeeded()
+    {
+        // repopulate filter with new scripts if top-up has happened since last iteration
+        for (const auto& [desc_spkm_id, last_range_end] : m_last_range_ends) {
+            auto desc_spkm{dynamic_cast<DescriptorScriptPubKeyMan*>(m_wallet.GetScriptPubKeyMan(desc_spkm_id))};
+            assert(desc_spkm != nullptr);
+            int32_t current_range_end{desc_spkm->GetEndRange()};
+            if (current_range_end > last_range_end) {
+                AddScriptPubKeys(desc_spkm, last_range_end);
+                m_last_range_ends.at(desc_spkm->GetID()) = current_range_end;
+            }
+        }
+    }
+
+    std::optional<bool> MatchesBlock(const uint256& block_hash) const
+    {
+        return m_wallet.chain().blockFilterMatchesAny(BlockFilterType::BASIC, block_hash, m_filter_set);
+    }
+
+private:
+    const CWallet& m_wallet;
+    /** Map for keeping track of each range descriptor's last seen end range.
+      * This information is used to detect whether new addresses were derived
+      * (that is, if the current end range is larger than the saved end range)
+      * after processing a block and hence a filter set update is needed to
+      * take possible keypool top-ups into account.
+      */
+    std::map<uint256, int32_t> m_last_range_ends;
+    GCSFilter::ElementSet m_filter_set;
+
+    void AddScriptPubKeys(const DescriptorScriptPubKeyMan* desc_spkm, int32_t last_range_end = 0)
+    {
+        for (const auto& script_pub_key : desc_spkm->GetScriptPubKeys(last_range_end)) {
+            m_filter_set.emplace(script_pub_key.begin(), script_pub_key.end());
+        }
+    }
+};
 } // namespace
 
 std::shared_ptr<CWallet> LoadWallet(WalletContext& context, const std::string& name, std::optional<bool> load_on_start, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error, std::vector<bilingual_str>& warnings)
@@ -1755,7 +1814,11 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
     uint256 block_hash = start_block;
     ScanResult result;
 
-    WalletLogPrintf("Rescan started from block %s...\n", start_block.ToString());
+    std::unique_ptr<FastWalletRescanFilter> fast_rescan_filter;
+    if (!IsLegacy() && chain().hasBlockFilterIndex(BlockFilterType::BASIC)) fast_rescan_filter = std::make_unique<FastWalletRescanFilter>(*this);
+
+    WalletLogPrintf("Rescan started from block %s... (%s)\n", start_block.ToString(),
+                    fast_rescan_filter ? "fast variant using block filters" : "slow variant inspecting all blocks");
 
     fAbortRescan = false;
     ShowProgress(strprintf("%s " + _("Rescanning…").translated, GetDisplayName()), 0); // show rescan progress in GUI as dialog or on splashscreen, if rescan required on startup (e.g. due to corruption)
@@ -1782,9 +1845,22 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
             WalletLogPrintf("Still rescanning. At block %d. Progress=%f\n", block_height, progress_current);
         }
 
-        // Read block data
-        CBlock block;
-        chain().findBlock(block_hash, FoundBlock().data(block));
+        bool fetch_block{true};
+        if (fast_rescan_filter) {
+            fast_rescan_filter->UpdateIfNeeded();
+            auto matches_block{fast_rescan_filter->MatchesBlock(block_hash)};
+            if (matches_block.has_value()) {
+                if (*matches_block) {
+                    LogPrint(BCLog::SCAN, "Fast rescan: inspect block %d [%s] (filter matched)\n", block_height, block_hash.ToString());
+                } else {
+                    result.last_scanned_block = block_hash;
+                    result.last_scanned_height = block_height;
+                    fetch_block = false;
+                }
+            } else {
+                LogPrint(BCLog::SCAN, "Fast rescan: inspect block %d [%s] (WARNING: block filter not found!)\n", block_height, block_hash.ToString());
+            }
+        }
 
         // Find next block separately from reading data above, because reading
         // is slow and there might be a reorg while it is read.
@@ -1793,35 +1869,41 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
         uint256 next_block_hash;
         chain().findBlock(block_hash, FoundBlock().inActiveChain(block_still_active).nextBlock(FoundBlock().inActiveChain(next_block).hash(next_block_hash)));
 
-        if (!block.IsNull()) {
-            LOCK(cs_wallet);
-            if (!block_still_active) {
-                // Abort scan if current block is no longer active, to prevent
-                // marking transactions as coming from the wrong block.
-                result.last_failed_block = block_hash;
-                result.status = ScanResult::FAILURE;
-                break;
-            }
-            for (size_t posInBlock = 0; posInBlock < block.vtx.size(); ++posInBlock) {
-                SyncTransaction(block.vtx[posInBlock], TxStateConfirmed{block_hash, block_height, static_cast<int>(posInBlock)}, fUpdate, /*rescanning_old_block=*/true);
-            }
-            // scan succeeded, record block as most recent successfully scanned
-            result.last_scanned_block = block_hash;
-            result.last_scanned_height = block_height;
+        if (fetch_block) {
+            // Read block data
+            CBlock block;
+            chain().findBlock(block_hash, FoundBlock().data(block));
+
+            if (!block.IsNull()) {
+                LOCK(cs_wallet);
+                if (!block_still_active) {
+                    // Abort scan if current block is no longer active, to prevent
+                    // marking transactions as coming from the wrong block.
+                    result.last_failed_block = block_hash;
+                    result.status = ScanResult::FAILURE;
+                    break;
+                }
+                for (size_t posInBlock = 0; posInBlock < block.vtx.size(); ++posInBlock) {
+                    SyncTransaction(block.vtx[posInBlock], TxStateConfirmed{block_hash, block_height, static_cast<int>(posInBlock)}, fUpdate, /*rescanning_old_block=*/true);
+                }
+                // scan succeeded, record block as most recent successfully scanned
+                result.last_scanned_block = block_hash;
+                result.last_scanned_height = block_height;
 
-            if (save_progress && next_interval) {
-                CBlockLocator loc = m_chain->getActiveChainLocator(block_hash);
+                if (save_progress && next_interval) {
+                    CBlockLocator loc = m_chain->getActiveChainLocator(block_hash);
 
-                if (!loc.IsNull()) {
-                    WalletLogPrintf("Saving scan progress %d.\n", block_height);
-                    WalletBatch batch(GetDatabase());
-                    batch.WriteBestBlock(loc);
+                    if (!loc.IsNull()) {
+                        WalletLogPrintf("Saving scan progress %d.\n", block_height);
+                        WalletBatch batch(GetDatabase());
+                        batch.WriteBestBlock(loc);
+                    }
                 }
+            } else {
+                // could not scan block, keep scanning but record this block as the most recent failure
+                result.last_failed_block = block_hash;
+                result.status = ScanResult::FAILURE;
             }
-        } else {
-            // could not scan block, keep scanning but record this block as the most recent failure
-            result.last_failed_block = block_hash;
-            result.status = ScanResult::FAILURE;
         }
         if (max_height && block_height >= *max_height) {
             break;