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Redis concurrency control
const redis = require('redis');
const bluebird = require('bluebird');
const redisClient = redis.createClient({});
bluebird.promisifyAll(Object.getPrototypeOf(redisClient));
const luaScript = `
local newPayload = ARGV[1]
local newVersionStr, newData = ARGV[1]:match("^([0-9]+)|(.+)$")
local prevVal = redis.call("get", KEYS[1]) or nil
if prevVal == nil then
return redis.call("set", KEYS[1], "1|" .. newData)
end
local oldVersionStr, oldData = prevVal:match("^([0-9]+)|(.+)$")
local newVersion = tonumber(newVersionStr)
local oldVersion = tonumber(oldVersionStr)
-- check if version matches before writing
if oldVersion == (newVersion - 1) then
return redis.call('set', KEYS[1], newPayload)
else
return nil
end
`;
(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'));
})();
@arch1995

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@arch1995 arch1995 commented Apr 10, 2021

What should we do when we get null?

@Munawwar

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Owner Author

@Munawwar 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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