【进阶实战】榜单读写分离：查询走只读实例封装

local function writeScore(actorName, delta)
    execTransaction("UPDATE arena SET score=score+" .. delta ..
        " WHERE name='" .. actorName .. "'")
    setsysvarex("ReplicaLag", os.time(), 1)
end
local function readRank(page)
    local ok, rows = pcall(queryReplica,
        "SELECT name,score FROM arena ORDER BY score DESC LIMIT 20 OFFSET " .. (page - 1) * 20)
    if ok and rows then
        return rows, false
    end
    return queryMaster("SELECT name,score FROM arena ORDER BY score DESC LIMIT 20"), true
end
local function showRank(actorName, page)
    local actor = getplayerbyname(actorName)
    local rows, degraded = readRank(page)
    if degraded then
        sendmsg(actor, 1, "榜单查询切换主库，响应稍慢。")
    end
    for i, r in ipairs(rows) do
        sendmsg(actor, 1, (page - 1) * 20 + i .. ". " .. r.name .. " " .. r.score)
    end
end

local function confirmPaid(orderId)
    return queryMaster("SELECT state FROM orders WHERE id=" .. orderId)
end