Whenever -blocksonly is specified, there is implicitly a zero size mempool. However, there is still a non-zero value for -maxmempool which will be shared with dbcache, leading to 300 MB extra usage. Fix this.
.check_ratio = chainparams.DefaultConsistencyChecks() ? 1 : 0,
    };
    if (const auto err{ApplyArgsManOptions(args, chainparams, mempool_opts)}) {
        return InitError(*err);
    }
    mempool_opts.check_ratio = std::clamp<int>(mempool_opts.check_ratio, 0, 1'000'000);
    int64_t descendant_limit_bytes = mempool_opts.limits.descendant_size_vbytes * 40;
    if (mempool_opts.max_size_bytes < 0 || mempool_opts.max_size_bytes < descendant_limit_bytes) {
        return InitError(strprintf(_("-maxmempool must be at least %d MB"), std::ceil(descendant_limit_bytes  1'000'000.0)));
    }
    LogPrintf("* Using %.1f MiB for in-memory UTXO set (plus up to %.1f MiB of unused mempool space)\n", cache_sizes.coins * (1.0  1024  1024), mempool_opts.max_size_bytes * (1.0  1024  1024));
    for (bool fLoaded = false; !fLoaded && !ShutdownRequested();) {
        node.mempool = std::make_unique<CTxMemPool>(mempool_opts);
        node.chainman = std::make_unique<ChainstateManager>(chainman_opts);
        ChainstateManager& chainman = *node.chainman;
        node::ChainstateLoadOptions options;
        options.mempool = Assert(node.mempool.get());
        options.reindex = node::fReindex;
        options.reindex_chainstate = fReindexChainState;
        options.prune = node::fPruneMode;
        options.check_blocks = args.GetIntArg("-checkblocks", DEFAULT_CHECKBLOCKS);
        options.check_level = args.GetIntArg("-checklevel", DEFAULT_CHECKLEVEL);
        options.check_interrupt = ShutdownRequested;
        options.coins_error_cb = [] {
            uiInterface.ThreadSafeMessageBox(
                _("Error reading from database, shutting down."),
                "", CClientUIInterface::MSG_ERROR);
        };
        uiInterface.InitMessage(_("Loading block index…").translated);
        const auto load_block_index_start_time{SteadyClock::now()};