735927 - NS_ERROR_FAILURE accessing nsITelemetrySessionData.snapshots in TelemetryPing.js :: getSessionPayloadAndSlug

Status: RESOLVED DUPLICATE of bug 735768

(Toolkit :: Telemetry, defect)

Description

[Matthew N. [:MattN]]

Mentioned in bug 707320 comment 50 and then I ran into it when testing telemetry through scratchpad.  In my case this may be expected since I may not have everything initialized properly when I try test pings but filing just in case it's the cause of the decreased telemetry rates[1].

I only seem to get this exception when a sessionHistrograms.dat* file exists in my profile.  If I delete it before starting the browser then the telemetry test ping is sent fine.

This is what I'm running in the scratchpad in the chrome environment:

let SERVER = "https://data.mozilla.com";
let TelemetryPing = Cc["@mozilla.org/base/telemetry-ping;1"].getService(Ci.nsIObserver);
TelemetryPing.observe(null, "test-gather-startup", null);
TelemetryPing.observe(null, "test-ping", SERVER);

When I was digging into the call stack earlier the error was from |this._prevSession.snapshots| on https://mxr.mozilla.org/mozilla-central/source/toolkit/components/telemetry/TelemetryPing.js?rev=60ebef177e6d#450

IIRC it had to do with a mismatch in count when reading sessionHistograms.dat* but I can't find my notes now so I'll dig in again and post what's happening.

[1] https://blog.mozilla.com/nfroyd/2012/03/13/data-gathering-the-old-fashioned-way/

Comment 1

[Matthew N. [:MattN]]

Bug 735768 seems to fix this.  With those patches applied, I don't get an exception and two test pings are sent to the server when I have a savedHistograms.dat* file.

Build identifier: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:14.0) Gecko/20120314 Firefox/14.0a1