[gmaxwell@argonaut src]$ ./bitcoin-cli getblockstats 101
{
  "avgfee": 0,
  "avgfeerate": 0,
  "avgtxsize": 0,
  "blockhash": "00000000b69bd8e4dc60580117617a466d5c76ada85fb7b87e9baea01f9d9984",
  "feerate_percentiles": [
    0,
    0,
    0,
    0,
    0
  ],
  "height": 101,
  "ins": 0,
  "maxfee": 0,
  "maxfeerate": 0,
  "maxtxsize": 0,
  "medianfee": 0,
  "mediantime": 1231657185,
  "mediantxsize": 0,
  "minfee": 0,
  "minfeerate": 0,
  "mintxsize": 0,
  "outs": 1,
  "subsidy": 5000000000,
  "swtotal_size": 0,
  "swtotal_weight": 0,
  "swtxs": 0,
  "time": 1231661741,
  "total_out": 0,
  "total_size": 0,
  "total_weight": 0,
  "totalfee": 0,
  "txs": 1,
  "utxo_increase": 1,
  "utxo_size_inc": 117
}
[gmaxwell@argonaut src]$ ./bitcoin-cli getblockstats 100000
error code: -8
error message:
One or more of the selected stats requires -txindex enabled

Stats that require txindex should always fail if txindex isn't enabled and the stat is requested, and those stats should not be offered by default.

Also, although the help says it will accept a '1. "hash_or_height"     (string or numeric, required) The block hash or height of the target block', that doesn't seem to work regardless of how I quote it.

[gmaxwell@argonaut src]$ ./bitcoin-cli getblockstats "0000000000000000001b98c07fca289e1ca3358aeabdcca9b7f7ba704d83a3d4"
error: Error parsing JSON:0000000000000000001b98c07fca289e1ca3358aeabdcca9b7f7ba704d83a3d4



{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            "gettxoutsetinfo\n"
            "\nReturns statistics about the unspent transaction output set.\n"
            "Note this call may take some time.\n"
            "\nResult:\n"
            "{\n"
            "  \"height\":n,     (numeric) The current block height (index)\n"
            "  \"bestblock\": \"hex\",   (string) The hash of the block at the tip of the chain\n"
            "  \"transactions\": n,      (numeric) The number of transactions with unspent outputs\n"
            "  \"txouts\": n,            (numeric) The number of unspent transaction outputs\n"
            "  \"bogosize\": n,          (numeric) A meaningless metric for UTXO set size\n"
            "  \"hash_serialized_2\": \"hash\", (string) The serialized hash\n"
            "  \"disk_size\": n,         (numeric) The estimated size of the chainstate on disk\n"
            "  \"total_amount\": x.xxx          (numeric) The total amount\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("gettxoutsetinfo", "")