<p>I have to pass parameters between two rails apps. In one side (sender) I have an array of hashes. I have a code like the following to send the data:</p>

<pre><code>   http = Net::HTTP.new('localhost', '3030')
   result = http.post('/processar_lotes', my_array_of_hashes)
</code></pre>

<p>Some questions</p>

<ul>
<li>Is there any (kind of) serialize or something like this that I can pass to the other app?</li>
<li>At the other side, how can I de-serialize the information?</li>
<li>Is there a limit to the size of what I pass as a parameter?</li>
</ul>

Considering that these objects can vary per file size, and your computer's specs (bus speed, HD speed) affect this, the only way to be sure is to write your own benchmark.  Just create a simple for loop, count from 1 to 1000, and read the file inside the loop over and over (but do not create and destroy the objects inside the loop, just focus on the reading part).
Of course this whole exercise reeks of pre-optimization, which can lead to bad coding habit.  Just write your code in the most readable, simple fashion, and if there is a speed problem, refactor as needed.
But since it's a small amount of data, I would say it won't matter.