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: 
I'm afraid there is no such built-in functionality as of today.
But you can use any kind of distributed cache, like memcached or Redis. Those caching solutions are really easy to use.
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.