`getblock` is slow on verbosity, it's happened because `LOCK(cs_main)` applied for whole function including JSON generation
https://github.com/bitcoin/bitcoin/blob/ef70f9b52b851c7997a9f1a0834714e3eebc1fd8/src/rpc/blockchain.cpp#L810

I added few lines which print spent time:
```cpp
    LOCK(cs_main);
    auto t1 = std::chrono::high_resolution_clock::now();
...
    auto t2 = std::chrono::high_resolution_clock::now();
    auto ret = blockToJSON(block, pblockindex, verbosity >= 2);
    auto t3 = std::chrono::high_resolution_clock::now();
    std::cout << "blockToJSON " << pblockindex->nHeight << ": " << std::chrono::duration_cast<std::chrono::microseconds>(t2 - t1).count() << " " << std::chrono::duration_cast<std::chrono::microseconds>(t3 - t1).count() << std::endl;
    return ret;
```

and numbers looks like:
```
blockToJSON 570019: 14727 201870
blockToJSON 570022: 16049 225224
blockToJSON 570021: 33776 217398
blockToJSON 570020: 21754 191669
blockToJSON 570023: 30949 236941
blockToJSON 570025: 23346 223673
blockToJSON 570024: 18732 203002
blockToJSON 570026: 17467 216213
blockToJSON 570027: 16658 217395
blockToJSON 570028: 19015 219183
```

i.e. everything before JSON generation takes 15-30ms, while JSON takes minimum 190ms and lock `cs_main` for all this time. As result it's possible extract only ~5 blocks per second.

Looking on the code I think it's possible copy data from `CBlockIndex` to extra structure, so in this case `cs_main` can be unlocked right after `GetBlockChecked`.
https://github.com/bitcoin/bitcoin/blob/ef70f9b52b851c7997a9f1a0834714e3eebc1fd8/src/rpc/blockchain.cpp#L828
As result `getblock` in verbosity mode should be much faster (in case if `-rpcthreads` will be adjusted too).

Does this make sense?
}
        }
        
        UniValue unspents(UniValue::VARR);
        std::vector<CTxOut> input_txos;
        std::map<COutPoint, Coin> coins;
        g_should_abort_scan = false;
        g_scan_progress = 0;
        int64_t count = 0;
        std::unique_ptr<CCoinsViewCursor> pcursor;
        {
            LOCK(cs_main);
            FlushStateToDisk();
            pcursor = std::unique_ptr<CCoinsViewCursor>(pcoinsdbview->Cursor());
            assert(pcursor);
        }
        bool res = FindScriptPubKey(g_scan_progress, g_should_abort_scan, count, pcursor.get(), needles, coins);
        result.pushKV("success", res);
        result.pushKV("searched_items", count);
        for (const auto& it : coins) {
            const COutPoint& outpoint = it.first;
            const Coin& coin = it.second;
            const CTxOut& txo = coin.out;
            input_txos.push_back(txo);
            total_in += txo.nValue;
            UniValue unspent(UniValue::VOBJ);
            unspent.pushKV("txid", outpoint.hash.GetHex());
            unspent.pushKV("vout", (int32_t)outpoint.n);
            unspent.pushKV("scriptPubKey", HexStr(txo.scriptPubKey.begin(), txo.scriptPubKey.end()));
            unspent.pushKV("desc", descriptors[txo.scriptPubKey]);