how to halt meteorjs collection subscription

Question

how to halt meteorjs collection subscription

I am facing an issue with stopping a subscription process.

Here is the current code I am using:

if (Meteor.isClient) {

    Meteor.autorun(function(){
        var query;
        query = Session.get('search.query');
        if (!query) return;
        if (Envi.temp.searchSubscribtion) {
            console.log('Subscription for search needs to be stopped ... ');
            Envi.temp.searchSubscribtion.stop();
        }

        Envi.temp.searchSubscribtion = Meteor.subscribe('search', query, {
            onReady : function () {
                console.log('Finished.');
            }
        });
    });

}

'Env' is a global function where subscriptions are temporarily stored in temp.searchSubscribtion.

The issue at hand: when I change the value of search.query to a query that retrieves all items, the "Finished" console log is displayed after about 1 minute.

However, when I change search.query to a query that retrieves only a few items, the "Finished" console log displays after approximately 5 seconds.

It seems there is a difference in processing time between long and short queries.

My goal now is to cancel the currently running subscription when a query is changed, and start a new one. However, when I switch from a long query to a short query immediately, the "Finished" console log still takes more than 1 minute to display.

Even though "

Envi.temp.searchSubscribtion.stop();

" is being executed (as seen in the console log), the subscription does not stop - it appears that the server finishes the first subscription before moving on to the second, as if they are queued.

Do you have any ideas on how to effectively cancel a running subscription?

javascript meteor

Answer 1

Answer №1

As the original query is taking a considerable amount of time to return, it causes the single Fiber responsible for running your subscriptions to be stalled. This means that you won't be able to send any other subscription commands (such as stop or new subscription) until the initial query completes.

To address this issue, there are several options available:

Optimize the query for faster execution (consider using indexes).
Publish all documents with limited fields and perform the search on the client side. You can then subscribe to the full set of fields by sending a list of _id's.
Avoid using a publication and instead send data via Meteor.methods (non-reactive/auto-publish).
Combine options 2 and 3; create a meteor method to execute the query and return a list of _id's, then subscribe to that list of _id's.
Implement option 4 but utilize a server-side route to prevent blocking meteor methods when making multiple calls.

When utilizing Meteor.methods, ensure to prevent fiber blocking by following these steps:

When calling from the client, use

Meteor.apply('myMethod',[parameter1, parameter2 /* etc */], {wait: false}, callback);

.

In the method on the server side, call this.unblock() within the method body.

An example implementation for option 4 is provided below:

if (Meteor.isServer) {
  Meteor.methods('search', function (query) {
    this.unblock();
    // implement query logic
    return _.pluck(collection.find(query, {_id: true}).fetch(), '_id');
  });

  Meteor.publish('searchResults', function (resultIds) {
    return collection.find({_id: {$in: resultIds}});
  });
}
if (Meteor.isClient) {

  Meteor.autorun(function () {
    var query;
    query = Session.get('search.query');
    if (!query) return;
    Meteor.apply('search', [query], {wait:false}, function (err, resultIds) {
      if (err) {
        console.log('error!', err);
        return;
      }
      var currentSearch = Session.get('search.query');
      if (!EJSON.equals(currentSearch, query)) {
        console.log('Results returned for', query, ' however current search is ', currentSearch);
        return;
      }

      if (Envi.temp.searchSubscribtion) {
        console.log('Subscription for search needs to be stopped... ');
        Envi.temp.searchSubscribtion.stop();

      }
      Envi.temp.searchSubscribtion = Meteor.subscribe('searchResults', resultIds, {
        onReady: function () {
          console.log('Query complete for:', query);
        }
      });
    });
  });

}

Answer 2

As the original query is taking a considerable amount of time to return, it causes the single Fiber responsible for running your subscriptions to be stalled. This means that you won't be able to send any other subscription commands (such as stop or new subscription) until the initial query completes.

To address this issue, there are several options available:

Optimize the query for faster execution (consider using indexes).
Publish all documents with limited fields and perform the search on the client side. You can then subscribe to the full set of fields by sending a list of _id's.
Avoid using a publication and instead send data via Meteor.methods (non-reactive/auto-publish).
Combine options 2 and 3; create a meteor method to execute the query and return a list of _id's, then subscribe to that list of _id's.
Implement option 4 but utilize a server-side route to prevent blocking meteor methods when making multiple calls.

When utilizing Meteor.methods, ensure to prevent fiber blocking by following these steps:

When calling from the client, use

Meteor.apply('myMethod',[parameter1, parameter2 /* etc */], {wait: false}, callback);

.

In the method on the server side, call this.unblock() within the method body.

An example implementation for option 4 is provided below:

if (Meteor.isServer) {
  Meteor.methods('search', function (query) {
    this.unblock();
    // implement query logic
    return _.pluck(collection.find(query, {_id: true}).fetch(), '_id');
  });

  Meteor.publish('searchResults', function (resultIds) {
    return collection.find({_id: {$in: resultIds}});
  });
}
if (Meteor.isClient) {

  Meteor.autorun(function () {
    var query;
    query = Session.get('search.query');
    if (!query) return;
    Meteor.apply('search', [query], {wait:false}, function (err, resultIds) {
      if (err) {
        console.log('error!', err);
        return;
      }
      var currentSearch = Session.get('search.query');
      if (!EJSON.equals(currentSearch, query)) {
        console.log('Results returned for', query, ' however current search is ', currentSearch);
        return;
      }

      if (Envi.temp.searchSubscribtion) {
        console.log('Subscription for search needs to be stopped... ');
        Envi.temp.searchSubscribtion.stop();

      }
      Envi.temp.searchSubscribtion = Meteor.subscribe('searchResults', resultIds, {
        onReady: function () {
          console.log('Query complete for:', query);
        }
      });
    });
  });

}

how to halt meteorjs collection subscription

Answer №1

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