Limit blocks by BDB locks required.

This is a temporary measure to make the rebased client "compatible" with
the old BDB-based one.

Based on
bitcoin/bitcoin@8c222dc.

TODO

@@ -1,7 +1,8 @@
 * soft fork in namecoind:
+  + prevent "name_new stealing" in memory pool
+  + enforce nametx-version also for name *outputs*
   - limit DB locks / unique tx
   - disallow greedy names
-  - enforce nametx-version also for name *outputs*
   - disallow auxpow parent blocks with auxpow
   - update fee logic?
 

src/main.cpp

@@ -2485,6 +2485,43 @@ bool FindUndoPos(CValidationState &state, int nFile, CDiskBlockPos &pos, unsigne
     return true;
 }
 
+/* Temporary check that blocks are compatible with BDB's 10,000 lock limit.
+   This is based on Bitcoin's commit 8c222dca4f961ad13ec64d690134a40d09b20813.
+   Each "object" touched in the DB may cause two locks (one read and one
+   write lock).  Objects are transaction IDs and names.  Thus, count the
+   total number of transaction IDs (tx themselves plus all distinct inputs).
+   In addition, each Namecoin transaction could touch at most one name,
+   so add them as well.  */
+bool CheckDbLockLimit(const CBlock& block, const CTransaction* extraTx)
+{
+    std::vector<CTransaction> vtx = block.vtx;
+    if (extraTx)
+        vtx.push_back(*extraTx);
+
+    set<uint256> setTxIds;
+    unsigned nNames = 0;
+    BOOST_FOREACH(const CTransaction& tx, vtx)
+    {
+        setTxIds.insert(tx.GetHash());
+        if (tx.IsNamecoin())
+            ++nNames;
+
+        BOOST_FOREACH(const CTxIn& txIn, tx.vin)
+            setTxIds.insert(txIn.prevout.hash);
+    }
+
+    const unsigned nTotalIds = setTxIds.size() + nNames;
+
+    if (nTotalIds > 4500)
+        return error("%s : %u locks estimated, that is too much for BDB",
+                     __func__, nTotalIds);
+
+    if (fDebug)
+        LogPrintf ("%s : need %u locks\n", __func__, nTotalIds);
+
+    return true;
+}
+
 bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool fCheckPOW)
 {
     // Check proof of work matches claimed amount
@@ -2534,6 +2571,12 @@ bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW, bo
         return state.DoS(100, error("CheckBlock() : size limits failed"),
                          REJECT_INVALID, "bad-blk-length");
 
+    // Enforce the temporary DB lock limit.
+    // TODO: Remove with a hardfork in the future.
+    if (!CheckDbLockLimit(block))
+        return state.DoS(100, error("%s : DB lock limit failed", __func__),
+                         REJECT_INVALID, "bad-db-locks");
+
     // First transaction must be coinbase, the rest must not be
     if (block.vtx.empty() || !block.vtx[0].IsCoinBase())
         return state.DoS(100, error("CheckBlock() : first tx is not coinbase"),

src/main.h

@@ -388,6 +388,9 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
 /** Apply the effects of this block (with given index) on the UTXO set represented by coins */
 bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex, CCoinsViewCache& coins, std::set<valtype>& expiredNames, bool fJustCheck = false);
 
+// TODO: Remove when this check is no longer necessary.
+bool CheckDbLockLimit(const CBlock& block, const CTransaction* extraTx = NULL);
+
 /** Context-independent validity checks */
 bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool fCheckPOW = true);
 bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW = true, bool fCheckMerkleRoot = true);

src/miner.cpp

@@ -243,6 +243,10 @@ CBlockTemplate* CreateNewBlock(const CScript& scriptPubKeyIn)
             if (nBlockSize + nTxSize >= nBlockMaxSize)
                 continue;
 
+            // Check the DB lock limit won't be exceeded.
+            if (!CheckDbLockLimit(*pblock, &tx))
+                continue;
+
             // Legacy limits on sigOps:
             unsigned int nTxSigOps = GetLegacySigOpCount(tx);
             if (nBlockSigOps + nTxSigOps >= MAX_BLOCK_SIGOPS)

src/rpcmining.cpp

@@ -454,10 +454,10 @@ Value getblocktemplate(const Array& params, bool fHelp)
         throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid mode");
 
     if (vNodes.empty())
-        throw JSONRPCError(RPC_CLIENT_NOT_CONNECTED, "Bitcoin is not connected!");
+        throw JSONRPCError(RPC_CLIENT_NOT_CONNECTED, "Namecoin is not connected!");
 
     if (IsInitialBlockDownload())
-        throw JSONRPCError(RPC_CLIENT_IN_INITIAL_DOWNLOAD, "Bitcoin is downloading blocks...");
+        throw JSONRPCError(RPC_CLIENT_IN_INITIAL_DOWNLOAD, "Namecoin is downloading blocks...");
 
     static unsigned int nTransactionsUpdatedLast;