Merge #541: Blockindex compatibility fix, startup speedup

0baa135 Only check 1 in 1000 block header sigs on load (Gregory Sanders)
87c06d4 Save some space, maintain compatibility with elements-0.14 header index (Gregory Sanders)

Pull request description:

  We diverged from the 0.14 codebase, fix included here as well as performance speedup on initial load.

  In 0.14 we did no signature checking at all, but the signature checks were what alerted me to the incompatibility, so I opted to preserve some of that as sanity check.

Tree-SHA512: 565c9d771e8f7a1057f7dcd1107c9d3f23159d3cf9f9968fdc53f7732abdfbf8a65e3c0a42807fbb80c712cb65d6fa2a7c83c3bf3de5ac0a6b72b49e55f00e83

src/chain.h

@@ -210,7 +210,6 @@ class CBlockIndex
     int32_t nVersion;
     uint256 hashMerkleRoot;
     uint32_t nTime;
-    uint32_t block_height;
     uint32_t nBits;
     uint32_t nNonce;
     CProof proof;
@@ -240,7 +239,6 @@ class CBlockIndex
         nVersion       = 0;
         hashMerkleRoot = uint256();
         nTime          = 0;
-        block_height   = 0;
         nBits          = 0;
         nNonce         = 0;
         proof.SetNull();
@@ -258,7 +256,6 @@ class CBlockIndex
         nVersion       = block.nVersion;
         hashMerkleRoot = block.hashMerkleRoot;
         nTime          = block.nTime;
-        block_height   = block.block_height;
         nBits          = block.nBits;
         nNonce         = block.nNonce;
         proof          = block.proof;
@@ -290,7 +287,9 @@ class CBlockIndex
             block.hashPrevBlock = pprev->GetBlockHash();
         block.hashMerkleRoot = hashMerkleRoot;
         block.nTime          = nTime;
-        block.block_height   = block_height;
+        if (g_con_blockheightinheader) {
+            block.block_height = nHeight;
+        }
         block.nBits          = nBits;
         block.nNonce         = nNonce;
         block.proof          = proof;
@@ -411,7 +410,6 @@ class CDiskBlockIndex : public CBlockIndex
         READWRITE(hashPrev);
         READWRITE(hashMerkleRoot);
         READWRITE(nTime);
-        READWRITE(block_height);
         // For compatibility with elements 0.14 based chains
         if (g_signed_blocks) {
             READWRITE(proof);
@@ -428,7 +426,9 @@ class CDiskBlockIndex : public CBlockIndex
         block.hashPrevBlock   = hashPrev;
         block.hashMerkleRoot  = hashMerkleRoot;
         block.nTime           = nTime;
-        block.block_height    = block_height;
+        if (g_con_blockheightinheader) {
+            block.block_height = nHeight;
+        }
         block.nBits           = nBits;
         block.nNonce          = nNonce;
         block.proof           = proof;

src/txdb.cpp

@@ -307,7 +307,6 @@ bool CBlockTreeDB::LoadBlockIndexGuts(const Consensus::Params& consensusParams,
                 CBlockIndex* pindexNew = insertBlockIndex(diskindex.GetBlockHash());
                 pindexNew->pprev          = insertBlockIndex(diskindex.hashPrev);
                 pindexNew->nHeight        = diskindex.nHeight;
-                pindexNew->block_height   = diskindex.block_height;
                 pindexNew->nFile          = diskindex.nFile;
                 pindexNew->nDataPos       = diskindex.nDataPos;
                 pindexNew->nUndoPos       = diskindex.nUndoPos;
@@ -321,7 +320,9 @@ bool CBlockTreeDB::LoadBlockIndexGuts(const Consensus::Params& consensusParams,
                 pindexNew->nTx            = diskindex.nTx;
 
                 const uint256 block_hash = pindexNew->GetBlockHash();
-                if (!CheckProof(pindexNew->GetBlockHeader(), consensusParams) &&
+                // Only validate one of every 1000 block header for sanity check
+                if (pindexNew->nHeight % 1000 == 0 &&
+                        !CheckProof(pindexNew->GetBlockHeader(), consensusParams) &&
                     block_hash != consensusParams.hashGenesisBlock) {
                     return error("%s: CheckProof: %s, %s", __func__, block_hash.ToString(), pindexNew->ToString());
                 }