title: Nifi: Merging all of necessary flowfile in one shot with MergeContent Processor
body: <p>This is the question about MergeContent processor in Nifi.
  Currently, I need to combine all flowfiles with one particular attribute in one shot manner.</p>
  
  <p>But what happens is since there are so many flowFile with the same attribute, 
  the processor produces a few different flowfiles merged with the attribute, and those few should be combined into one big flowfile together. </p>
  
  <p>Are they any ways to wait for all flowfile with same attribute to come into the MergeContent Processor and merge all of them at one time?</p>
  
  <p>If not, what could be an alternative?</p>