How to avoid data loss during server failure using MongoDB on the same machine?

Question

I read that mongoDB does not write data to disk immediately, it does this periodically.

Any thoughts on how to deal with this?

Answer 1

You can enable logging with --journal .

Check out http://www.adathedev.co.uk/2011/03/mongodb-journaling-performance-single.html and http://www.mongodb.org/display/DOCS/Durability+and+Repair

Answer 2

In addition to --journal , which is enabled by default, since MongoDB 2.0 ( only on 64-bit machines), there is a flag that you can set when saving data:

• safe => false : don't wait for db response
• safe => true : wait for db response
• safe => num : wait for many servers to have a record before returning
• fsync => true : write fsync to disk before returning. fsync => true implies safe=>true , but not vice versa.

If fsync=>false and safe=>true and the record can be successfully applied to the mmapped file, but not yet written to disk