Problem with index TTL and differences between 	Logical Data Size and Storage Size

Adrien_Le_Clair · 2024-10-21T16:03:38.248Z

After using a TTL index on a collection, I noticed after several months that the Disk Usage never decreases. After a compact, I did recover my Disk Usage but only on the primary node, how to do it on the secondary one ? Did it did something wrong with TTL index to need compact operation ?

Ernesto_Lluesma_Bravo · 2024-10-22T10:38:20.589Z

Hello Adrien,

You need to run the compact in every secondary that you have in your replica set. The TTL index doesn’t trigger any compact so, it needs to be done manually.

Otherwise, I don’t know why you expect a decrease on disk usage.

If you could tell me more about it, it would be fine.

Adrien_Le_Clair · 2024-10-22T12:22:56.891Z

We have seen that we have been near our limit of 40go, after having deleting a lot of document from a collection, we expected to lower it to not reach it. After the compact operation it has been ok, lower to 6go.

I understand that we have to do it manually but I don’t understand how do it on secondary ones.

Ernesto_Lluesma_Bravo · 2024-10-22T13:50:05.754Z

Please, take a look at this explained answer:

Compacting a replica set Ops and Admin

Hi @Mark_De_May and welcome to the MongoDB Community forums. To connect to a secondary member you would use mongo (installed 5.0.x and earlier) or mongosh (installed with 6.0.x and later). Something like the following: mongosh mongodb://<URI or IP of secondary>:<port> -u <user> -p <other parameters as needed> Note that we are not passing in the password so it will prompt you for that. This is the safe way as your password is not exposed on the command line or in the command history. O…

Also it is given some great advices!

Adrien_Le_Clair · 2024-10-22T14:18:56.970Z

Many thanks, I will try this

Ernesto_Lluesma_Bravo · 2024-10-22T14:34:49.118Z

Please, when you try it, let me know if it is the solution.

Thank you!

Adrien_Le_Clair · 2024-10-23T12:45:42.996Z

It works, just needed directConnection param at true. Thanks again