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Proposed commit message (D7)
Issue #1081266 by stefan.r, jeroen.b, mikeytown2, tsphethean, mfb, joseph.olstad, marcelovani, Fabianx: Avoid re-scanning module directory when a filename or a module is missing
Drupal occurs a performance deficit when multiple filenames (ie. modules, themes) are missing or moved. The deficit occurs because we do a file scan perpetually to look for missing modules on certain pages, such as admin/config.
For D8: We remove the "missing file scan" that happens in
drupal_get_filename() altogether and do various workarounds to deal with this scan in places where we haven't cached file locations yet, such as in the installer and in some tests (see #351). Instead of a file scan, we now do a
trigger_error(), informing the developer/administrator about the missing file.
For D7: We cache any missing files in a static variable as well as in cache_bootstrap (for 24 hours, or until we visit the themes/modules overview page). We also do a trigger_error() as soon as we find a missing file in the drupal_get_filename() call.
In a followup issue we can check for this in hook_requirements() as well.
User interface changes
In D8, we remove the file scan from drupal_get_filename(), which also affects drupal_get_path(). The lack of this is only a "problem" in the installer, in tests and during module rebuild, which are not part of the API.
Original report by mfb
This patch provides a performance boost for sites that are missing modules (common on old sites which have been maintained for many years). In this case, drupal_system_listing() and file_scan_directory() will be called over and over looking for missing modules on certain pages, such as admin/config.
This patch adds an additional static variable to drupal_get_filename() to store an array of mask-directory combinations that have been scanned. Once one scan has been performed for a particular extension in a particular directory, there is no need to run the same scan later in the same request.
This information will be cached in 'drupal_get_filename:missing' in cache_bootstrap as well. Invalidation of this cache happens upon running cron, and upon visiting the themes/modules overview pages.
Beta phase evaluation
|Issue category||Bug because significant performance slowdown|
|Issue priority||Major because significant performance slowdown.|
|Prioritized changes||The main goal of this issue is performance|