[plasmashell] [Bug 521757] plasmashell 6.7.0 pegs one CPU core after update to 6.7.0; perf shows KActivities::Stats / SQLite; clearing kactivitymanagerd resources fixes it

https://bugs.kde.org/show_bug.cgi?id=521757

[email protected] changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugs.overpass613@passinbox.
                   |                            |com

--- Comment #1 from [email protected] ---
Maybe i've found the Root cause of the CPU/SQLite thrashing, found via
heaptrack while
investigating a related plasmashell freeze/leak: every call to
KActivities::Stats::ResultWatcher::resultRemoved() re-runs a full SQLite
query from scratch (ResultModelPrivate::fetch() -> new ResultSet ->
QSQLiteResult::prepare/reset) instead of updating incrementally. In a
14-minute heaptrack session this call chain alone accounted for
139051509 allocation calls.

Full call stack:
KActivities::Stats::ResultWatcher::resultRemoved(QString const&)
 -> KActivities::Stats::ResultModelPrivate::fetch(int, int)
 -> KActivities::Stats::ResultSet::ResultSet(KActivities::Stats::Query)
 -> QSQLiteResult::prepare()/reset() -> sqlite3 parse+exec -> malloc

On my system (3 panels, each with a Kicker "frequently used" widget wired
to KActivitiesStats) this also caused plasmashell's main thread to get
stuck for long periods inside glibc's allocator (systrim/sbrk) while
freeing the resulting QSqlQuery objects, eventually leading to
plasma-plasmashell.service being killed by the timeout watchdog. RSS grew
70-440MB/minute while this was happening.

Workaround that fixed it completely for me: System Settings -> Privacy ->
disable "Track application and file usage" (org.kde.ActivityManager.
Resources.Scoring). RSS went flat immediately after.

Versions: Plasma 6.7.4, KDE Frameworks 6.29.0, Qt 6.11.1, Fedora 44, Wayland.

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