Question: How to store the temporary data in Apache storm?

In storm topology, bolt needs to access the previously processed data.

```
Eg: if the bolt processes varaiable1 with result as 20 at 10:00 AM.

```

and again `varaiable1` is received as `50` at `10:15 AM` then the result should be `30 (50-20)` 

later if varaiable1 receives `70` then the result should be `20 (70-50)` at `10:30`.

How to achieve this functionality.

Answer: 
In short, you wanted to do micro-batching calculations with in storm’s running tuples.
First you need to define/find key in tuple set. 
Do field grouping(don't use shuffle grouping) between bolts using that key. This will guarantee related tuples will always send to same task of downstream bolt for same key.
Define class level collection List/Map to maintain old values and add new value in same for calculation, don’t worry they are thread safe between different executors instance of same bolt.
There are a couple of approaches to do that but it depends on your system requirements, your team skills and your infrastructure.

You could use Apache Cassandra for you events storing and you pass the row's key in the tuple so the next bolt could retrieve it.

If your data is time series in nature, then maybe you would like to have a look at [OpenTSDB](http://opentsdb.net/) or [InfluxDB](http://influxdb.com/).

You could of course fall back to something like Software Transaction Memory but I think that would needs good amount of crafting.