I'm guessing this affects both activity stream and discovery stream:

Warning: attempting to write 5837 bytes to preference browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions. This is bad for general performance and memory usage. Such an amount of data should rather be written to an external file. This preference will not be sent to any content processes.

I can reproduce this.

1. Set Discovery Stream pref "browser.newtabpage.activity-stream.discoverystream.config" to "{"enabled":true,"show_spocs":true,"layout_endpoint":"https://getpocket.com/v3/newtab/layout?version=1&consumer_key=40249-e88c401e1b1f2242d9e441c4&layout_variant=basic" }"
2. Load a new tab.
3. Refresh that new tab.
4. Check and note browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions
5. Refresh that tab again.
6. Check and note browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions again.
7. repeat steps 5-6.

Expected: browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions should cap out and stop growing at 3 impressions.
Actual: browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions keeps growing bigger and bigger the more you refresh.

[Tracking Requested - why for this release]:

Is there anything you need me to do? I can track this for 66 and make sure to follow up to see that it lands. At this point, you will need to request uplift to beta.

@lizzard, I'm not sure, but I think we're good? I just pushed up an update to the patch, so once that lands in github/nightly, I can start the uplift process.

https://hg.mozilla.org/mozilla-central/rev/a4a56d03930a

I'm trying to reproduce issue but can't figure out how and where exactly should I check step 4 "Check and note browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions".

Could you please clarify this to me?
Thanks.

It's fixed on nightly, and I don't think the issue is present on release.

It might be there on beta, so I bet beta is the best place to start trying to reproduce the original issue.

I get that it's fixed on the Nightly now, but I tried to reproduce it on a Nightly build from January 28 and also on Firefox 66.0b6.

What I wanted to know is where should I look for/where should it be displayed "browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions"?

I'm not sure if this helps, but I'll try to just break down that step a bit more, hopefully helps :)

4.a. Open about:config in a new tab.
4.b. Search for the pref browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions
4.c. Take note of the value in that pref, specifically the length, it should be something along the lines of: {"786":[1549640147446,1549640147635,1549640149830,1549640149969],"1256":[1549637509386,1549637529656,1549637529798,1549637530066,1549637530231]} but your numbers may vary.

6.a Check the pref value in step 4.c again, it should be larger now.

Does that help a bit?

Thanks for the details.

But the thing is that I'm not able to see this pref "browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions" in about:config and I don't know why, even after I set Discovery Stream pref "browser.newtabpage.activity-stream.discoverystream.config" to "{"enabled":true,"show_spocs":true,"layout_endpoint":"https://getpocket.com/v3/newtab/layout?version=1&consumer_key=40249-e88c401e1b1f2242d9e441c4&layout_variant=basic" }"

I tried on Nightly 66.0a1 (2019-01-27) and on Firefox 66.0b6.

The only three pref's that could be related to the one mentioned are these:
"browser.newtabpage.activity-stream.feeds.section.topstories"
"browser.newtabpage.activity-stream.feeds.section.topstories.options"
"services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.section.topstories"

Is there any thing extra I should do to be able to see this pref "browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions"?

Thanks.

Maybe you somehow have spocs disabled? If it's a new profile though, I don't see how that would be possible.

To double check, look for the pref "showSponsored"

I can verify this if it's easier.

"browser.newtabpage.activity-stream.showSponsored" pref is set to "true" so my guess is that it's not disabled.

Could you please verify this bug?
Thanks.

Ohhhh, I wonder if it's a locale thing, as I think we only ship spocs to en-US!

I also tried to connect to US VPN and to change "browser.search.region" pref to "US", but that didn't help.
I'm not able to see this pref "browser.newtabpage.activity-stream.feeds.section.topstories.spoc.impressions" in about:config.

Do you have any other suggestions how to do that?

Actually I finally managed to reproduce it on Nightly 67.0a1 (2019-01-28).

Verified as fixed on Firefox Nightly 67.0a1 (2019-02-13) on Windows 10 x 64, Mac OS X 10.14 and on Ubuntu 16.04 x64.

Can you request uplift? Thanks.

I wonder if we're fine on this now and no longer require an uplift. Previously we needed this because both discovery and activity stream were using the TELEMETRY_IMPRESSION_STATS event, now discovery stream is using DISCOVERY_STREAM_IMPRESSION_STATS in another uplift https://github.com/mozilla/activity-stream/commit/9a91d03b05f99a46016bcd4134b876b6a4f9c5ca, which should also stop the leaking event.

The commit you link to in comment 19 seems to be connected with bug 1522832 which landed on m-c (for nightly 67) but isn't on 66 be ta yet. Should it be? If so can you request uplift there?

Yeah sounds like bug 1522832 is now going through the uplift process.

This one was initially a quicker fix and fixing the core problem, bug 1522832 changed the code path this one was fixing for, so the issue is not currently being hit. bug 1522832 wasn't initially intended for uplift when this one was tagged, but it ended up being needed, and tagged before this one.

I'm pretty sure I can mark this as 66 wont fix, but let me know if I did something wrong in this process.

Although, I'm going to add some verification steps for this bug to bug 1522832 to ensure it does get fixed in beta.