As discovered in bug 1187864 comment 4, Telemetry is reporting repeated annotations for thread hangs [1]. In a particular sample ping, I found repeated annotations which summed up to a 2.2Mb blob. We should probably address this issue by collapsing identical annotations entries. [1] - https://pastebin.mozilla.org/8847691

This patch stacks on the one from bug 1213780.

Using nsAutoString instead of nsString.

Backout: https://hg.mozilla.org/integration/fx-team/rev/e9cae6188ca4

This patch works around the rooting issue detected by the hazard analysis. After a discussion with sfink (thanks!), the issue turned out to be a false positive. It was addressed by returning the JS array using a MutableObjectHandle parameter rather then returning the JSObject pointer. Function '_ZN12_GLOBAL__N_1L23CreateJSHangAnnotationsEP9JSContextRKN7mozilla6VectorINS2_9UniquePtrINS2_11HangMonitor15HangAnnotationsENS2_13DefaultDeleteIS6_EEEELm0ENS2_17MallocAllocPolicyEEE|Telemetry.cpp:JSObject* {anonymous}::CreateJSHangAnnotations(JSContext*, const class mozilla::Vector<mozilla::UniquePtr<mozilla::HangMonitor::HangAnnotations> >*)' has unrooted '<returnvalue>' of type 'JSObject*' live across GC call '_ZN12nsTHashtableI15nsStringHashKeyED1Ev|nsTHashtable<EntryType>::~nsTHashtable() [with EntryType = nsStringHashKey]' at toolkit/components/telemetry/Telemetry.cpp:2956 toolkit/components/telemetry/Telemetry.cpp:2956: Assign(57,58, return := __temp_23**) toolkit/components/telemetry/Telemetry.cpp:2956: Call(58,59, reportedAnnotations.~nsTHashtable()) [[GC call]] toolkit/components/telemetry/Telemetry.cpp:2956: Call(59,60, annotationsArray.~Rooted()) toolkit/components/telemetry/Telemetry.cpp:2957: [[end of function]]

https://hg.mozilla.org/integration/fx-team/rev/56707eeec6e53453878731864eaac19ef1a0c5ab Bug 1215540 - Fix Telemetry reporting repeated hang annotations for Thread hangs. r=aklotz

Can we uplift this to Beta 43? See https://bugzilla.mozilla.org/show_bug.cgi?id=1211411#c11 Btw, was there a bug to limit the # of threadHang stacks reported to telemetry? (not just their depth)

Comment on attachment 8679403 [details] [diff] [review] bug1215540.patch Approval Request Comment [Feature/regressing bug #]: Remove duplicated annotations for thread hangs, consistently reducing the size of the pings sent to Telemetry servers. [User impact if declined]: This isn't a user-facing feature. However, without this patches bug 1222894 could potentially cause sending a lot of oversized pings, wasting both storage and processing time server side, thus increasing costs. [Describe test coverage new/current, TreeHerder]: This has been on m-c for 2 weeks without any reported issue. Thread hangs are xpcshell-test covered (test_ThreadHangStats.js) [Risks and why]: Low risk. This only touches Telemetry & Thread Hang stacks, no front facing features or other systems. [String/UUID change made/needed]: None. Please note that this is part of an uplift stack required for bug 1222894. This is the stack (the patches correctly apply in order to mozilla-beta): 1213780, 1211411, 1215540, 1219751.

Marking affected for 43 since we intend to uplift this

Comment on attachment 8679403 [details] [diff] [review] bug1215540.patch Reducing size of telemetry ping info, please uplift to beta.

Oops.

(In reply to Vladan Djeric (:vladan) -- please needinfo! PTO Nov 16/19/20 from comment #11) > Btw, was there a bug to limit the # of threadHang stacks reported to > telemetry? (not just their depth) Ouch, sorry, I forgot to answer that one. No, we didn't put any hard limit in place, as the other measures fixed all the big ping samples that I had.