There might be room for performance improvements - currently for each $query, PhabricatorApplication::isClassInstalledForViewer is called again though some queries share the same application.

In D25501#14443, @aklapper wrote:

This also needs rework because I still get a Query overheated when not being logged in and going to http://phorge.localhost/feed/transactions/query/all/

Are there any feed transactions that are visible to logged out users? Maybe that feed page should just 404 when logged out?

In D25501#14458, @20after4 wrote:

Are there any feed transactions that are visible to logged out users?

Yes, basically all. See https://we.phorge.it/feed/transactions/query/advanced/ in a private browser window

In what case, a class can be installed "for the viewer", but generally uninstalled?

Edited: sorry I get this. I think that application "Visible to: (Registered) Users" triggers the "not installed".

Right. Sorry, my previous comment was very misleading!

It makes sense thanks. Minor note:

If the application is not visible (false), there is no need to also check for isClassInstalled() (that may return true). This can also lead to a situation where the app is not visible to that user, but the query is shown.

Maybe we can simplify things introducing a commodity "if viewer exists" method like:

// Remove TransactionQuery classes of uninstalled apps. Increases query
// performance and decreases likeliness of an "Query Overheated" error if
// an app got uninstalled so data in it cannot be accessed anymore anyway.
// See https://secure.phabricator.com/T13133, https://we.phorge.it/T15642
foreach ($queries as $key => $query) {
  $app = $query->getQueryApplicationClass();
  if ($app !== null && PhabricatorApplication::isClassInstalledForViewerIfAny($app, $viewer)) {
    unset($queries[$key]);
  }
}

final public static isClassInstalledForViewerIfAny(
  $class,
  PhabricatorUser $viewer) {

  return $viewer
    ? self::isClassInstalledForViewer( $class, $viewer )
    : self::isClassInstalled( $class );
}

In D25501#15033, @valerio.bozzolan wrote:

Maybe we can simplify things introducing a commodity "if viewer exists" method like:

I like that idea.