We currently use MongoDB 3.0 with MMAP storage, and would like to upgrade to 3.2 WiredTiger. What is the best order?

[Daniel Galinkin]

Hello guys,

As explained in the subject, we currently use MongoDB 3.0 with MMAP storage, and would like to upgrade to 3.2 WiredTiger.

What would be the best course of action?

- First upgrade the storage to wired tiger, and then upgrade the mongo version, or;

- upgrade the mongo version first, maintaining the storage engine, and then upgrade it to wired tiger?

Regards,

Daniel

[Allan Bazinet]

Personal experience, we updated to 3.2 first, then to WiredTiger.  The 3.0 to 3.2 upgrade was done in-place, i.e., on the same servers, then the WT conversion was done as a rolling upgrade to new servers.  It went fine.  The things I'd recommend looking at closely pre-flight are  (a) ensure you've got enough replication log window to support a rolling upgrade and (b) closely monitor the I/O after the first secondary is replicated -- in our case, we found the journal on WT to be much more write-intensive than MMAP.  If you're using the Mongo hosted backup, be sure to convert your format there to WT when done.  Overall, other than the time required, it was a non-event for us.

[Daniel Galinkin]

Nice, thanks for the feedback Allan!