wallet: skip block scan if block was created before wallet birthday

To avoid wasting processing power, we can skip blocks that occurred
before the wallet's creation time,  since these blocks are guaranteed
not to contain any relevant wallet data.

This has direct implications (an speed improvement) on the underlying
blockchain synchronization process as well.

The reason is that the validation interface queue is limited to
10 tasks per time. This means that no more than 10 blocks can be
waiting for the wallet(s) to be processed while we are synchronizing
the chain (activating the best chain to be more precise).
Which can be a bottleneck if blocks arrive and are processed faster
from the network than what they are  processed by the wallet(s).

4 files changed, 42 insertions, 6 deletions

diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 953fdb63b6..1c8d65c583 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -710,6 +710,8 @@ void LegacyScriptPubKeyMan::UpdateTimeFirstKey(int64_t nCreateTime)
     } else if (!nTimeFirstKey || nCreateTime < nTimeFirstKey) {
         nTimeFirstKey = nCreateTime;
     }
+
+    NotifyFirstKeyTimeChanged(this, nTimeFirstKey);
 }
 
 bool LegacyScriptPubKeyMan::LoadKey(const CKey& key, const CPubKey &pubkey)
@@ -2736,6 +2738,8 @@ void DescriptorScriptPubKeyMan::UpdateWalletDescriptor(WalletDescriptor& descrip
     m_map_script_pub_keys.clear();
     m_max_cached_index = -1;
     m_wallet_descriptor = descriptor;
+
+    NotifyFirstKeyTimeChanged(this, m_wallet_descriptor.creation_time);
 }
 
 bool DescriptorScriptPubKeyMan::CanUpdateToWalletDescriptor(const WalletDescriptor& descriptor, std::string& error)
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index 22b67c88e9..5c7240823f 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -256,6 +256,9 @@ public:
 
     /** Keypool has new keys */
     boost::signals2::signal<void ()> NotifyCanGetAddressesChanged;
+
+    /** Birth time changed */
+    boost::signals2::signal<void (const ScriptPubKeyMan* spkm, int64_t new_birth_time)> NotifyFirstKeyTimeChanged;
 };
 
 /** OutputTypes supported by the LegacyScriptPubKeyMan */
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index dc8112c081..d5268afbf6 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1436,6 +1436,12 @@ void CWallet::blockConnected(const interfaces::BlockInfo& block)
 
     m_last_block_processed_height = block.height;
     m_last_block_processed = block.hash;
+
+    // No need to scan block if it was created before the wallet birthday.
+    // Uses chain max time and twice the grace period to adjust time for block time variability.
+    if (block.chain_time_max < m_birth_time.load() - (TIMESTAMP_WINDOW * 2)) return;
+
+    // Scan block
     for (size_t index = 0; index < block.data->vtx.size(); index++) {
         SyncTransaction(block.data->vtx[index], TxStateConfirmed{block.hash, block.height, static_cast<int>(index)});
         transactionRemovedFromMempool(block.data->vtx[index], MemPoolRemovalReason::BLOCK);
@@ -1779,6 +1785,14 @@ bool CWallet::ImportScriptPubKeys(const std::string& label, const std::set<CScri
     return true;
 }
 
+void CWallet::FirstKeyTimeChanged(const ScriptPubKeyMan* spkm, int64_t new_birth_time)
+{
+    int64_t birthtime = m_birth_time.load();
+    if (new_birth_time < birthtime) {
+        m_birth_time = new_birth_time;
+    }
+}
+
 /**
  * Scan active chain for relevant transactions after importing keys. This should
  * be called whenever new keys are added to the wallet, with the oldest key
@@ -3107,6 +3121,14 @@ std::shared_ptr<CWallet> CWallet::Create(WalletContext& context, const std::stri
     // Try to top up keypool. No-op if the wallet is locked.
     walletInstance->TopUpKeyPool();
 
+    // Cache the first key time
+    std::optional<int64_t> time_first_key;
+    for (auto spk_man : walletInstance->GetAllScriptPubKeyMans()) {
+        int64_t time = spk_man->GetTimeFirstKey();
+        if (!time_first_key || time < *time_first_key) time_first_key = time;
+    }
+    if (time_first_key) walletInstance->m_birth_time = *time_first_key;
+
     if (chain && !AttachChain(walletInstance, *chain, rescan_required, error, warnings)) {
         return nullptr;
     }
@@ -3182,11 +3204,7 @@ bool CWallet::AttachChain(const std::shared_ptr<CWallet>& walletInstance, interf
     {
         // No need to read and scan block if block was created before
         // our wallet birthday (as adjusted for block time variability)
-        std::optional<int64_t> time_first_key;
-        for (auto spk_man : walletInstance->GetAllScriptPubKeyMans()) {
-            int64_t time = spk_man->GetTimeFirstKey();
-            if (!time_first_key || time < *time_first_key) time_first_key = time;
-        }
+        std::optional<int64_t> time_first_key = walletInstance->m_birth_time.load();
         if (time_first_key) {
             FoundBlock found = FoundBlock().height(rescan_height);
             chain.findFirstBlockWithTimeAndHeight(*time_first_key - TIMESTAMP_WINDOW, rescan_height, found);
@@ -3500,7 +3518,10 @@ LegacyScriptPubKeyMan* CWallet::GetOrCreateLegacyScriptPubKeyMan()
 
 void CWallet::AddScriptPubKeyMan(const uint256& id, std::unique_ptr<ScriptPubKeyMan> spkm_man)
 {
-    m_spk_managers[id] = std::move(spkm_man);
+    const auto& spkm = m_spk_managers[id] = std::move(spkm_man);
+
+    // Update birth time if needed
+    FirstKeyTimeChanged(spkm.get(), spkm->GetTimeFirstKey());
 }
 
 void CWallet::SetupLegacyScriptPubKeyMan()
@@ -3533,6 +3554,7 @@ void CWallet::ConnectScriptPubKeyManNotifiers()
     for (const auto& spk_man : GetActiveScriptPubKeyMans()) {
         spk_man->NotifyWatchonlyChanged.connect(NotifyWatchonlyChanged);
         spk_man->NotifyCanGetAddressesChanged.connect(NotifyCanGetAddressesChanged);
+        spk_man->NotifyFirstKeyTimeChanged.connect(std::bind(&CWallet::FirstKeyTimeChanged, this, std::placeholders::_1, std::placeholders::_2));
     }
 }
 
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 6aa67737e8..e74eeb0a99 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -299,6 +299,10 @@ private:
     // Local time that the tip block was received. Used to schedule wallet rebroadcasts.
     std::atomic<int64_t> m_best_block_time {0};
 
+    // First created key time. Used to skip blocks prior to this time.
+    // 'std::numeric_limits<int64_t>::max()' if wallet is blank.
+    std::atomic<int64_t> m_birth_time{std::numeric_limits<int64_t>::max()};
+
     /**
      * Used to keep track of spent outpoints, and
      * detect and report conflicts (double-spends or
@@ -645,6 +649,9 @@ public:
     bool ImportPubKeys(const std::vector<CKeyID>& ordered_pubkeys, const std::map<CKeyID, CPubKey>& pubkey_map, const std::map<CKeyID, std::pair<CPubKey, KeyOriginInfo>>& key_origins, const bool add_keypool, const bool internal, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
     bool ImportScriptPubKeys(const std::string& label, const std::set<CScript>& script_pub_keys, const bool have_solving_data, const bool apply_label, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+    /** Updates wallet birth time if 'new_birth_time' is below it */
+    void FirstKeyTimeChanged(const ScriptPubKeyMan* spkm, int64_t new_birth_time);
+
     CFeeRate m_pay_tx_fee{DEFAULT_PAY_TX_FEE};
     unsigned int m_confirm_target{DEFAULT_TX_CONFIRM_TARGET};
     /** Allow Coin Selection to pick unconfirmed UTXOs that were sent from our own wallet if it