Last Comment Bug 770883 - Disable functionality for clearing prefetch
: Disable functionality for clearing prefetch
Product: Core
Classification: Components
Component: Widget: Win32 (show other bugs)
: Trunk
: x86_64 Windows 7
-- normal (vote)
: mozilla16
Assigned To: Brian R. Bondy [:bbondy]
: Jason Smith [:jsmith]
: Jim Mathies [:jimm]
Depends on: 692255
Blocks: 770899 770911
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Reported: 2012-07-04 07:17 PDT by Brian R. Bondy [:bbondy]
Modified: 2012-07-14 18:31 PDT (History)
7 users (show)
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Crash Signature:
QA Whiteboard:
Iteration: ---
Points: ---
Has Regression Range: ---
Has STR: ---

Patch v1 (5.34 KB, patch)
2012-07-04 07:53 PDT, Brian R. Bondy [:bbondy]
taras.mozilla: review+
akeybl: approval‑mozilla‑aurora+
Details | Diff | Splinter Review

Description User image Brian R. Bondy [:bbondy] 2012-07-04 07:17:39 PDT
The STARTUP_USING_PRELOAD_TRIAL histogram in correlation to startup time analysis in Bug 765850 has shown us that other than the slowest 1% of startups, prefetch disabling hurts us.

We need to land a patch that disables the functionality of clearing prefetch, but keeps everything else in place.  

This task will ensure that clearing does not happens on beta (will be v15) and Release (will be v14) on the next migration.

We will request that this goes on Aurora (currently v15) after it lands on Nightly (currently v16).
Comment 1 User image Jason Smith [:jsmith] 2012-07-04 07:30:45 PDT
Hmm okay (makes sense after reading the analysis). For windows users that dogfood Aurora and Nightly, what should we do about the fact that they now have prefetch files that are 0 KB and read only? Are they permanently stuck with those prefetch files unless they explicitly go into C:\Windows\Prefetch and remove them? Or is there something we can do on our end?

Is this a permanent backout of this functionality or a pref off until a better approach is found?
Comment 2 User image Brian R. Bondy [:bbondy] 2012-07-04 07:33:11 PDT
I'll be posting a follow up email about how this will be reverted completely for all users including those of Aurora and Nightly a bit later today.  In short after the next migration I'll land a new patch on the new Nightly and Aurora that deletes prefetch files only if they are read only and 0 sized. Then that task itself will be reverted before the migration after that.   In the end, unfortunately this is probably a permanent backout.
Comment 3 User image Brian R. Bondy [:bbondy] 2012-07-04 07:53:30 PDT
Created attachment 639100 [details] [diff] [review]
Patch v1

The reason I'm just #if 0'ing it out is because there will be another patch in a bug I'm about to post that will re-add this functionality.  That new patch will not land until after the next migration.  It will re-add the functionality but change prefetch clearing so it deletes the prefetch only when it is 0 bytes and read-only.
Comment 4 User image (dormant account) 2012-07-05 11:15:59 PDT
Comment on attachment 639100 [details] [diff] [review]
Patch v1

Comment 5 User image Brian R. Bondy [:bbondy] 2012-07-08 18:47:33 PDT

Tested this patch on elm, also tested to make sure upgrades are fine and are unaffected since this touches the maintenance service.
Comment 6 User image Brian R. Bondy [:bbondy] 2012-07-08 18:48:41 PDT
Comment on attachment 639100 [details] [diff] [review]
Patch v1

[Approval Request Comment]
Bug caused by (feature/regressing bug #): bug 692255
User impact if declined: We don't want to clear people's prefetch on the Beta channel since we found that clearing is a net negative.
Testing completed (on m-c, etc.): Tested on elm already, pushed to m-i so should be on m-c soon too.
Risk to taking this patch (and alternatives if risky): Low
String or UUID changes made by this patch: None
Comment 7 User image Ed Morley [:emorley] 2012-07-09 04:49:34 PDT
Comment 8 User image Alex Keybl [:akeybl] 2012-07-12 15:23:06 PDT
Comment on attachment 639100 [details] [diff] [review]
Patch v1

[Triage Comment]
Low risk, prevents a new regression in FF15.
Comment 9 User image Jason Smith [:jsmith] 2012-07-12 17:31:31 PDT
Verified on Nightly.
Comment 10 User image Brian R. Bondy [:bbondy] 2012-07-13 06:49:26 PDT

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