# MongoDB traffic investigation. system.profile resizing

**URL:** <https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864>\
**Category:** Percona Operator for MongoDB\
**Created:** [December 8, 2025, 5:12pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864 "2025-12-08T17:12:25Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Stateros](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/stateros/32/2490_2.png) [@Stateros](https://forums.percona.com/u/Stateros)\
**Post date:** [December 8, 2025, 5:12pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864/1 "2025-12-08T17:12:25Z")

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Hello folks, I need help with MongoDB traffic investigation and resizing `system.profile` in Percona Operator

## Description:

I need to increase the size of the capped `system.profile` collection to capture more query history. Our cluster has **intensive traffic** , and most **read load goes to secondaries** , so the default 1 MB capped size is too small (we only see ~30 docs before rollover).

**Environment:**

- Sharded cluster (2 shards)

- Operator: **1.20.1**

- MongoDB: **7.0.18**

- PMM: **2.43.1**

**What I know:**  
MongoDB docs say:

> To change the size of the `system.profile` collection on a secondary, you must stop the secondary, run it as a standalone, and then perform the steps above. When done, restart the standalone as a member of the replica set.

**Questions:**

1. How can I perform this migration using the Percona Operator?

2. Are there **alternatives for traffic investigation** that work well with Percona Operator and MongoDB 7? (QAN is super, but it can’t tell me the user/appName and where it came from primary or replica)

## Expected Result:

1. Resize `system.profile` on all shards (including secondaries) to something like **100 -200MB**.
2. Get a better picture of executed queries for troubleshooting index usage and query patterns.

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**Author:** ![Ivan\_Groenewold](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/ivan_groenewold/32/6299_2.png) [@Ivan\_Groenewold](https://forums.percona.com/u/Ivan_Groenewold)\
**Post date:** [December 9, 2025, 1:39pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864/2 "2025-12-09T13:39:36Z")

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Hi, you can follow a rolling update process similar to what is described for index builds on this post:

> **[How to Perform Rolling Index Builds with Percona Operator for MongoDB](https://www.percona.com/blog/how-to-perform-rolling-index-builds-with-percona-operator-for-mongodb/)**
>
> Rolling Index Builds take advantage of the replica set architecture by building the index on a single non-primary member at a time.

Regarding your question 2, PMM should be able to tell you the user/appName and where it came from primary or replica… did you run into any problem with the filters?

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<div class="post-metadata">

**Author:** ![Stateros](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/stateros/32/2490_2.png) [@Stateros](https://forums.percona.com/u/Stateros)\
**Post date:** [December 9, 2025, 1:51pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864/3 "2025-12-09T13:51:01Z")

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@Ivan_Groenewold thanks for the clear instruction.

For PMM - yes, I have problem with filters. There are no user name detected for the mongodb deployments:

 ![image](https://us1.discourse-cdn.com/flex019/uploads/percona1/original/3X/c/2/c2e6737cfb38ad09202e3baf2112be1b4ed359a8.png)

also, i have an idea to add appName to the query metadata tab.

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<div class="post-metadata">

**Author:** ![Ivan\_Groenewold](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/ivan_groenewold/32/6299_2.png) [@Ivan\_Groenewold](https://forums.percona.com/u/Ivan_Groenewold)\
**Post date:** [December 11, 2025, 12:27pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864/4 "2025-12-11T12:27:19Z")

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did you try selecting the cluster name first? that should update the User Name filter. If still running into a problem I suggest you open a ticket in our jira so dev team can have a look at your logs

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<div class="post-metadata">

**Author:** ![Stateros](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/stateros/32/2490_2.png) [@Stateros](https://forums.percona.com/u/Stateros)\
**Post date:** [December 11, 2025, 12:38pm UTC](https://forums.percona.com/t/mongodb-traffic-investigation-system-profile-resizing/39864/5 "2025-12-11T12:38:28Z")

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that’s exactly what I did for screenshot. I have one PMM server for MySQL and MongoDB.

It doesn’t matter what filter I use for MongoDB it just doesn’t show users. For MySQL it works perfectly fine.