title: Mongodb collections are dropped automatically
body: <p>I have MongoDB database setup in a Linux server along with a tomcat and everything works great. But i noticed that every 2 or 4 days the whole database collections are dropped. I saw the log of the MongoDB:</p>
  
  <pre><code>Mon Jan 16 08:01:14.375 [PeriodicTask::Runner] task: DBConnectionPool-cleaner took: 11ms
  Mon Jan 16 08:01:14.404 [PeriodicTask::Runner] task: WriteBackManager::cleaner took: 12ms
  Mon Jan 16 08:01:18.402 [TTLMonitor] query PLEASE_READ.system.indexes query: { expireAfterSeconds: { $exists: true } } ntoreturn:0 ntoskip:0 nscanned:1 keyUpdates:0 locks(micros) r:104348 nreturned:0 reslen:20 104ms
  Mon Jan 16 08:25:03.640 [initandlisten] connection accepted from 95.211.153.138:58622 #135 (7 connections now open)
  Mon Jan 16 08:25:04.286 [conn135] dropDatabase PLEASE_READ starting
  Mon Jan 16 08:25:04.287 [conn135] removeJournalFiles
  Mon Jan 16 08:25:04.490 [conn135] dropDatabase PLEASE_READ finished
  Mon Jan 16 08:25:04.508 [conn135] command PLEASE_READ.$cmd command: { dropDatabase: 1.0 } ntoreturn:1 keyUpdates:0 locks(micros) W:246737 reslen:62 246ms
  Mon Jan 16 08:25:04.579 [conn135] dropDatabase server_db starting
  Mon Jan 16 08:25:04.579 [conn135] removeJournalFiles
  Mon Jan 16 08:25:04.686 [conn135] dropDatabase server_db finished
  Mon Jan 16 08:25:04.686 [conn135] command server_db.$cmd command: { dropDatabase: 1.0 } ntoreturn:1 keyUpdates:0 locks(micros) W:107150 reslen:60 107ms
  Mon Jan 16 08:25:04.756 [conn135] dropDatabase local starting
  Mon Jan 16 08:25:04.756 [conn135] removeJournalFiles
  Mon Jan 16 08:25:04.780 [conn135] dropDatabase local finished
  Mon Jan 16 08:25:04.850 [conn135] dropDatabase admin starting
  Mon Jan 16 08:25:04.850 [conn135] removeJournalFiles
  Mon Jan 16 08:25:04.852 [conn135] dropDatabase admin finished
  Mon Jan 16 08:25:04.922 [conn135] dropDatabase test starting
  Mon Jan 16 08:25:04.922 [conn135] removeJournalFiles
  Mon Jan 16 08:25:04.926 [conn135] dropDatabase test finished
  Mon Jan 16 08:25:05.139 [conn135] allocating new ns file /var/lib/mongodb/WARNING.ns, filling with zeroes...
  Mon Jan 16 08:25:05.502 [FileAllocator] allocating new datafile /var/lib/mongodb/WARNING.0, filling with zeroes...
  Mon Jan 16 08:25:05.537 [FileAllocator] done allocating datafile /var/lib/mongodb/WARNING.0, size: 64MB,  took 0.009 secs
  Mon Jan 16 08:25:05.547 [FileAllocator] allocating new datafile /var/lib/mongodb/WARNING.1, filling with zeroes...
  Mon Jan 16 08:25:05.567 [conn135] build index WARNING.WARNING { _id: 1 }
  Mon Jan 16 08:25:05.569 [FileAllocator] done allocating datafile /var/lib/mongodb/WARNING.1, size: 128MB,  took 0.021 secs
  Mon Jan 16 08:25:05.592 [conn135] build index done.  scanned 0 total records. 0.023 secs
  Mon Jan 16 08:25:05.653 [conn135] insert WARNING.WARNING ninserted:1 keyUpdates:0 locks(micros) w:492848 513ms
  </code></pre>
  
  <p>I don't use a <a href="https://docs.mongodb.com/manual/tutorial/expire-data/" rel="nofollow noreferrer">TTL index</a> to any of the collections and i don't run any script in Linux to drop the database. </p>
  
  <p>My question is why the collections are dropped? Is it cause of the TTL?</p>
  
  <p>Thank you.</p>