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MongoDB - How to reduce storage size after deleting documents on replica set?


MongoDB does not free the disk space for OS use after deleting bunch of documents from the collection. We can reclaim that space using following cases.

  • By using compact command - Can be run on collections, but block all orations on database, need small downtime
  • By using repaireDatabase - Run on database need extra space and serious downtime
  • By dumping database and than drop and restore it - Time consuming and need downtime
  • By copy database using temporary name drop original and then re copy with original name - Time consuming and need downtime

Following is the best method of achieve same without downtime on replica set
  1. Step down secondary server
  2. Delete database files
  3. Start server, It will start Replica Set Initial Sync.
  4. After sync over do the same with other secondary servers one by one
  5. For primary server step it down.
  6. Make sure one of the secondary become primary
  7. Delete database file on primary
  8. Start primary server It will start Replica Set Initial Sync.
  9. After Replica Set Initial Sync complete it will become primary as per your replica set configuration
  10. Done, that's it..
Check used disk space on each server..

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