@neoxr/promise-coalesce
v1.1.1
Published
Coalesces multiple promises for the same identifier into a single request
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promise-coalesce
Coalesces multiple promises for the same identifier into a single request.
Reduces load on downstream systems when requests occur at the same time, without dropping requests or needing exclusion locks or wait-and-retry attempts.
Install
With npm:
npm install promise-coalesce
With yarn:
yarn add promise-coalesce
Usage
import { coalesceAsync } from 'promise-coalesce';
await coalesceAsync('some-group-key', async () => {
/* your logic */
});
Example
Cache Miss Relief Buffer
import { coalesceAsync } from 'promise-coalesce';
// Imagine you want to retrieve a value, and you have a cache to speed things up.
// If the value isn't in the cache, you'll need to get it from the source system,
// which can be a time-consuming process like a database query or an API request.
async function getValue(cacheKey: string): Promise<YourData> {
// When multiple requests try to fetch the same value from the cache at the same time,
// because of the way async operations work, yielding the event loop at each `await`,
// then they will all try to get it from the cache.
let cachedValue = await cache.get(cacheKey);
// They will take turns checking the condition and all see that the value is missing.
if (!cachedValue) {
// Here's where `coalesceAsync` comes to the rescue!
// Instead of making multiple expensive calls to the source system,
// we use `coalesceAsync`` to ensure it's called only once, and other requests
// wanting the same cache key wait for the result.
cachedValue = await coalesceAsync<YourData>(cacheKey, async () => {
// Now, we fetch the value from the source system.
const sourceValue = await getSourceValue();
// We also cache it for future use.
await cache.set(cacheKey, sourceValue, ttl);
// Now, the value is in the cache, and future requests will avoid calling the source system
// until the cached data expires (based on TTL).
return sourceValue;
});
}
return cachedValue;
}
Credits
This solution is inspired by node-cache-manager's
CallbackFiller from the v4.x
line.
It was removed
in the v5.x
line, and promise-coalesce
is an attempt to recover that feature
while also being generic enough for other applications.