399572 - move sessionstore.js to CSIDL_LOCAL_APPDATA

Status: RESOLVED WONTFIX

(Firefox :: Session Restore, defect)

Description

[Jo Hermans]

see bug 398807 comment 3

Since session restore across multiple hosts isn't very useful (if you crash, you're probably going to retry on the same host), maybe we can save sessionstore.js in CSIDL_LOCAL_APPDATA (Local Settings). People who are running on Windows roaming accounts (used in many companies, like mine) will benefit greatly, because it will avoid several network accesses per page that is displayed.

I don't agree though with bug 398807 comment 4, that wants to save in CSIDL_LOCAL_APPDATA while surfing, and in the profile on exit.

Comment 1

[Simon Bünzli]

(In reply to comment #0)
> Since session restore across multiple hosts isn't very useful (if you crash,
> you're probably going to retry on the same host)

Note that session restore isn't just for the case of a crash: Tools -> Options -> Main -> Startup -> When Firefox starts: "Show my windows and tabs from last time" does the same after quitting regularly and without the Restore Session prompt. 

> because it will avoid several network accesses per page that is displayed.

We don't save sessionstore.js for every accessed page but at most every browser.sessionstore.interval milliseconds (defaults to 10000, i.e. at most every 10 seconds). Nonetheless, saving in-session sessionstore.js locally might result in a minimal perf gain.

> I don't agree though with bug 398807 comment 4, that wants to save in
> CSIDL_LOCAL_APPDATA while surfing, and in the profile on exit.

If sessionstore.js isn't saved in the profile on exit, regular session resuming will be break when you log in at a different machine with the same roaming profile. That's not acceptable and there's really no reason to do this (since on exit we save much more data to the profile anyway).

Comment 2

[Wayne Mery (:wsmwk)]

does this really affect talos, bug 398807?

Comment 3

[Wayne Mery (:wsmwk)]

Mike does this make any sense to you?

Comment 4

[Mike de Boer [:mikedeboer]]

Sorry for the late reply here! Per https://bugzilla.mozilla.org/show_bug.cgi?id=398807#c78 I think we can reasonably say that perf has much improved since the filing of this bug.
Regardless of that, I think that the trade-off between perf gain and added complexity is not something that can be won using this strategy.
We're doing file saves for sessionstore off the main thread now, so it won't block the browsers' main thread anymore. Having another - temporary - file save location is opening a surface for bugs in service reliability, which is even more important than perf.