CODEWITHSUNDEEP
meteor
user1411290
user1411290

Reputation: 63

DDP vs Straight MongoDB access for synching large amounts of data

We are building an app in Meteor that will be participating in an education ecosystem. There are a number of applications (e.g. a GradeBook, a Student Information System, a Reporting System...) that will all need to have their data stores kept in synch with Meteor. The datastore size will be in the hundreds of thousands of documents.

My understanding is that DDP is used to connect "clients" to a Meteor app (by subscribing to feeds when Meteor is pushing data changes and RPC to get the data in to Meteor). And a "client" is generally scoped to a user...so the size of the data set is relatively small compared to the universe of data (a teacher might have access to 100 of the 250K documents).

If I connected a Reporting System (as a "client") to Meteor with DDP, all data in the store would need to be synched...does that mean that every time the Reporting System lost the connection to Meteor, all data would be re-sent from Meteor to the DDP client? (because the Reporting System is interested in ALL the data)...and if that's the case, DDP wouldn't be the way to keep application in synch, right?...it's meant more for much smaller scoped data sets....and we should probably be interacting directly with Mongo to keep things synch.

Thanks! Mike

Upvotes: 2

Views: 1401

Answers (2)

Tarang
Tarang

Reputation: 75975

I think nate's answer goes perfect on what you should do especially considering the volume of data. And if you need to display a whole lot of data if you're using pages to use a paginated subscription so that you can enjoy the realtime functionality (if you decide to use it) without downloading it all at once. Keep in mind though that at the moment the data is sent down like this (for each session, so if the tab is closed and reopened it will be redone):

1 - Connect to DDP Server/Proxy (Long Polling now due to websocket issues with chrome)
2 - Establish a 'subscription'
3 - Fetch all data relevant to subscription (initial download)
4 - Subscription is complete, now the client will 'listen' for changes
5 - Any updates (remove/update/insert, etc) are sent down to the client

There really isn't a sync system at this point where old data is kept offline (in a localstorage or indexed db or anything) so that step no 3 can be avoided and only the syncs from that point would occur.

This is mind, if there is a connectivity interruption (e.g losing connectivitiy for a short peroid of time Meteor will lose connection to the DDP wire and when it reconnects it download everything again as if it were from scratch.

Upvotes: 2

nate-strauser
nate-strauser

Reputation: 2803

based on this http://meteor.com/blog/2012/03/21/introducing-ddp

Distributed Data Protocol. DDP is a standard way to solve the biggest problem facing client-side JavaScript developers: querying a server-side database, sending the results down to the client, and then pushing changes to the client whenever anything changes in the database.

it seems clear that any new DDP client, receives all data and then deltas as the data changes.

i would suggest that if your 'client' doesnt need reactivity / realtime updates / 2 way synching, you should pull the data directly from mongo and avoid the overhead of 'syncing'. for a 'reporting system' this should be perfectly acceptable, grab a bunch of data, generate reports. you shouldnt care about changing data in this context, just a snapshot and reports from that snapshot.

if you do need the more real time features, DDP is likely worth the overhead and initial setup difficulty.

Upvotes: 3

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