wallet: cut per-entry copies in listtransactions and gettransaction

- ListTransactions computes a tx's "size" once, lazily, through a const
  CTransaction reference instead of a slicing copy per entry.
- listtransactions copies the returned window once from the built array.
- OrderedTxItems can open the wallet DB read-only without a flush on close;
  listtransactions uses it, so a read-only RPC no longer forces a BDB
  checkpoint (ThreadFlushWalletDB still flushes about 2 s later).
- gettransaction hex-encodes the tx without copying it.

Output is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/wallet/rpcwallet.cpp

@@ -1788,6 +1788,11 @@ void ListTransactions(const CWalletTx& wtx, const string& strAccount, int nMinDe
     bool fAllAccounts = (strAccount == string("*"));
     bool involvesWatchonly = wtx.IsFromMe(ISMINE_WATCH_ONLY);
 
+    // "size" is a property of the transaction, not of an entry: compute it once, when the first
+    // entry is built, through a const reference instead of a by-value CTransaction copy.
+    bool fHaveTxSize = false;
+    uint64_t nTxSize = 0;
+
     // Sent
     if ((!listSent.empty() || nFee != 0) && (fAllAccounts || strAccount == strSentAccount))
     {
@@ -1804,7 +1809,11 @@ void ListTransactions(const CWalletTx& wtx, const string& strAccount, int nMinDe
             entry.push_back(Pair("fee", ValueFromAmount(-nFee)));
             if (fLong)
                 WalletTxToJSON(wtx, entry);
-            entry.push_back(Pair("size", static_cast<uint64_t>(GetSerializeSize(static_cast<CTransaction>(wtx), SER_NETWORK, PROTOCOL_VERSION))));
+            if (!fHaveTxSize) {
+                nTxSize = static_cast<uint64_t>(GetSerializeSize(static_cast<const CTransaction&>(wtx), SER_NETWORK, PROTOCOL_VERSION));
+                fHaveTxSize = true;
+            }
+            entry.push_back(Pair("size", nTxSize));
             ret.push_back(entry);
         }
     }
@@ -1849,7 +1858,11 @@ void ListTransactions(const CWalletTx& wtx, const string& strAccount, int nMinDe
                 entry.push_back(Pair("vout", r.vout));
                 if (fLong)
                     WalletTxToJSON(wtx, entry);
-                entry.push_back(Pair("size", static_cast<uint64_t>(GetSerializeSize(static_cast<CTransaction>(wtx), SER_NETWORK, PROTOCOL_VERSION))));
+                if (!fHaveTxSize) {
+                    nTxSize = static_cast<uint64_t>(GetSerializeSize(static_cast<const CTransaction&>(wtx), SER_NETWORK, PROTOCOL_VERSION));
+                    fHaveTxSize = true;
+                }
+                entry.push_back(Pair("size", nTxSize));
                 ret.push_back(entry);
             }
         }
@@ -1955,7 +1968,7 @@ UniValue listtransactions(const UniValue& params, bool fHelp, const CPubKey& myp
     UniValue ret(UniValue::VARR);
 
     std::list<CAccountingEntry> acentries;
-    CWallet::TxItems txOrdered = pwalletMain->OrderedTxItems(acentries, strAccount);
+    CWallet::TxItems txOrdered = pwalletMain->OrderedTxItems(acentries, strAccount, true);
 
     // iterate backwards until we have nCount items to return:
     for (CWallet::TxItems::reverse_iterator it = txOrdered.rbegin(); it != txOrdered.rend(); ++it)
@@ -1978,23 +1991,14 @@ UniValue listtransactions(const UniValue& params, bool fHelp, const CPubKey& myp
     if ((nFrom + nCount) > (int)ret.size())
         nCount = ret.size() - nFrom;
 
-    vector<UniValue> arrTmp = ret.getValues();
+    // ret is newest to oldest; the reply is its entries [nFrom, nFrom+nCount), oldest to newest.
+    // Copy them once, back to front, straight from ret's storage (no vector copy/erase/reverse).
+    UniValue result(UniValue::VARR);
+    const std::vector<UniValue>& vNewestFirst = ret.getValues();
+    for (int i = nFrom + nCount; i > nFrom; --i)
+        result.push_back(vNewestFirst[i - 1]);
 
-    vector<UniValue>::iterator first = arrTmp.begin();
-    std::advance(first, nFrom);
-    vector<UniValue>::iterator last = arrTmp.begin();
-    std::advance(last, nFrom+nCount);
-
-    if (last != arrTmp.end()) arrTmp.erase(last, arrTmp.end());
-    if (first != arrTmp.begin()) arrTmp.erase(arrTmp.begin(), first);
-
-    std::reverse(arrTmp.begin(), arrTmp.end()); // Return oldest to newest
-
-    ret.clear();
-    ret.setArray();
-    ret.push_backV(arrTmp);
-
-    return ret;
+    return result;
 }
 
 UniValue listaccounts(const UniValue& params, bool fHelp, const CPubKey& mypk)
@@ -2239,7 +2243,7 @@ UniValue gettransaction(const UniValue& params, bool fHelp, const CPubKey& mypk)
     ListTransactions(wtx, "*", 0, false, details, filter);
     entry.push_back(Pair("details", details));
 
-    string strHex = EncodeHexTx(static_cast<CTransaction>(wtx));
+    string strHex = EncodeHexTx(static_cast<const CTransaction&>(wtx));
     entry.push_back(Pair("hex", strHex));
 
     return entry;

src/wallet/wallet.cpp

@@ -1701,10 +1701,12 @@ int64_t CWallet::IncOrderPosNext(CWalletDB *pwalletdb)
     return nRet;
 }
 
-CWallet::TxItems CWallet::OrderedTxItems(std::list<CAccountingEntry>& acentries, std::string strAccount)
+CWallet::TxItems CWallet::OrderedTxItems(std::list<CAccountingEntry>& acentries, std::string strAccount, bool fReadOnlyDb)
 {
     AssertLockHeld(cs_wallet); // mapWallet
-    CWalletDB walletdb(strWalletFile);
+    // Only a read cursor over the accounting entries runs on this handle. Pure readers open it
+    // read-only and without flush-on-close, so the call does not end in a txn_checkpoint.
+    CWalletDB walletdb(strWalletFile, fReadOnlyDb ? "r" : "r+", !fReadOnlyDb);
 
     // First: get all CWalletTx and CAccountingEntry into a sorted-by-order multimap.
     TxItems txOrdered;

src/wallet/wallet.h

@@ -1210,10 +1210,12 @@ public:
 
     /**
      * Get the wallet's activity log
+     * @param fReadOnlyDb open wallet.dat read-only and without flush-on-close (pure readers such as
+     *                    listtransactions: no txn_checkpoint per call); false = read-write, flush-on-close
      * @return multimap of ordered transactions and accounting entries
      * @warning Returned pointers are *only* valid within the scope of passed acentries
      */
-    TxItems OrderedTxItems(std::list<CAccountingEntry>& acentries, std::string strAccount = "");
+    TxItems OrderedTxItems(std::list<CAccountingEntry>& acentries, std::string strAccount = "", bool fReadOnlyDb = false);
 
     void MarkDirty();
     bool UpdateNullifierNoteMap();