Firebase functions - database cache?

Question

How does one cache database data in firebase function?

Based on this SO answer, firebase caches data for as long as there is an active listener.

Considering the following example:

exports.myTrigger = functions.database.ref("some/data/path").onWrite((data, context) => {
    var dbRootRef = data.after.ref.root;
    dbRootRef.child("another/data/path").on("value", function(){});
    return dbRootRef.child("another/data/path").once("value").then(function(snap){/*process data*/})
}

This will cache the data but the question is - is this valid approach for server side? Should I call .off() at some point in time so it doesn't produce any issues since this call can scale quickly producing tons of '.on()' listeners? Or is it ok to keep 'on()' indefinitely?

This sounds like a XY problem. What are you trying to accomplish by keeping the data in memory? — Frank van Puffelen
– Frank van Puffelen, Commented Jul 28, 2018 at 14:13
Thanks @FrankvanPuffelen - seems like you are right about XY problem. My intention is to reduce database downloads that are happening on server side, ie firebase functions. So the function only downloads the required data if it's changed - client can perform multiple writes at "some/data/path" but I want to minimize a number of reads at "another/data/path" — vir us
– vir us, Commented Jul 28, 2018 at 18:17

Frank van Puffelen · Accepted Answer · 2018-07-28 14:16:06Z

0

Since active data is kept in memory, your code will keep a snapshot of the latest data at another/data/path in memory as long as the listener is active. Since you never call off in your code, that will be as long as the container that runs the function is active, not just for the duration that this function is active.

Even if you have other Cloud Functions in that container, and those other functions don't need this data, it'll still be using memory.

If that is the behavior you want, then it's a valid approach. I'd just recommend doing a cost/benefit analysis, because I expect this may lead to hard-to-understand behavior at some point.

answered Jul 28, 2018 at 14:16

Frank van Puffelen

603k85 gold badges895 silver badges869 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

vir us Over a year ago

Thanks Frank - yes I want the data to persist across multiple calls of the same function to reduce number of reads at "another/data/path". How can I calculate the cost of memory for that? Also wondering what are the potential problem with this that can lead to "hard-to-understand behavior"? My understanding is that there will always be actual data in cache which I'll request as needed - just wondering what I'm missing here.

vir us Over a year ago

One more quick question - is it ok to call "on" multiple times on the same data path or there are any inefficiencies connected with attaching multiple listeners?

Frank van Puffelen Over a year ago

If there is an active listener on a path, the data won't be redownloaded.

Collectives™ on Stack Overflow

Firebase functions - database cache?

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related