Q:

Active Record with postgres sometimes skip index

Working with Active Record in postgres in a  rails application, hosted in heroku I start to notice that sometimes the index of my database are been skipped. For example:

product id 
1000
1001
1003  <---- Missing the 1002

This is not happen all the time, and I am trying to figure out what is the issue. 
I check database logs, the server logs and also I call my clients and they said that they have no issue. But I need to know why this skipping scenarios is happening.
rails', '3.2.17'
activerecord (3.2.17)
pg (0.14.1)
pg_search (0.7.0)
I have my guess: this can be heroku issue, with Async Excect, but I have no idea. 

A:

Your transaction rolled back due to some invalid data.  Could be google spiders, or less savory robots trying to penetrate the site.  
Here's a stack overflow answer: How to reset Autoincremented Id when rollback occurs in sql
Autoincrement IDs should not be contiguous in a production environment.

