title: Postgres filled missing primary key
body: <p>I have a postgres table, and it's primary key is auto-increment unsigned int. As far as my knowledge of postgres takes me, postgres keeps these auto incrementing values as sequences. So if an entry is deleted from the table, and the specific primary key is dropped, the next inserted row, won't reuse the previously dropped primary key.</p>
  
  <p>Now, the table I mentioned, had the first 6 rows dropped a long time ago, (primary keys : 1,2,3,4,5,6 ), and meanwhile new entries have been inserted, but the strange thing is, that at some point in time,not exactly after the rows were dropped, those first few rows have been filled, and now the primary keys 1 to 6 are in use, even though postgres should have continued on.</p>
  
  <p>At some point in time, we had to deal with some bloating, and we dealt with it by vacuuming, but I do not think that to be the main cause of this issue.</p>
  
  <p>I know this type of question is missing some of the context and is difficult to debug something without actually seeing the problem, but the main issue again is why was the primary key reused?</p>
  
  <p>Hoping someone with more background and understanding on how postgres works might tell me about some hidden mechanics that I am not aware of.</p>
  
  <p>Thanks!</p>