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Last active July 12, 2021 16:22
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What would you like to do?
Redis concurrency control
const redis = require('redis');
const bluebird = require('bluebird');
const redisClient = redis.createClient({});
const luaScript = `
local newPayload = ARGV[1]
local newVersionStr, newData = ARGV[1]:match("^([0-9]+)|(.+)$")
local prevVal ="get", KEYS[1]) or nil
if prevVal == nil then
return"set", KEYS[1], "1|" .. newData)
local oldVersionStr, oldData = prevVal:match("^([0-9]+)|(.+)$")
local newVersion = tonumber(newVersionStr)
local oldVersion = tonumber(oldVersionStr)
-- check if version matches before writing
if oldVersion == (newVersion - 1) then
return'set', KEYS[1], newPayload)
return nil
(async () => {
const results = await Promise.all([
redisClient.evalAsync(luaScript, 1, 'cc', '1|{a: 1}'),
redisClient.evalAsync(luaScript, 1, 'cc', '1|{b: 2}'),
redisClient.evalAsync(luaScript, 1, 'cc', '2|{b: 2}'),
console.log(results); // potential output [ 'OK', null, 'OK' ]
console.log(await redisClient.getAsync('cc'));
console.log(await redisClient.delAsync('cc'));
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What should we do when we get null?

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Munawwar commented Apr 12, 2021

When you get back null, either show error to user

OR if automatic merge it's possible,
fetch data again, merge new data with old, increase the version number and try to write again.

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