Memory leak in the entity schema converter

This could be a duplicate of #3056540: taxonomy_post_update_make_taxonomy_term_revisionable() timeouts with large numbers of terms or one of the issues related to #3052464: Cannot update to 8.7.0 because of taxonomy_post_update_make_taxonomy_term_revisionable.

@doidd, very nice find!

Manually tested this with ~13K terms by checking memory usage with and without the patch, and the results speak for themselves :)

HEAD: 600.7 MiB
Patch: 81.4 MiB

+++ b/core/lib/Drupal/Core/Entity/Sql/SqlFieldableEntityTypeListenerTrait.php
@@ -220,6 +220,9 @@ protected function copyData(EntityTypeInterface $entity_type, EntityTypeInterfac
+    $temporary_storage->resetCache($entity_identifiers);

$entity_identifiers could be a list of ID or revision IDs, so we can't pass it directly to resetCache(). Instead, we should call resetCache() without any argument in order to clear everything.

Fixed in the patch attached.

Oops, forgot to attach the patch.

I think the patch as it stands will result in clearing the entire persistent entity cache each time, see #2635440: Document what cache clearing from ContentEntityStorageBase::resetCache() actually clears. However it should now be possible to empty entity.memory_cache directly - see https://www.drupal.org/node/2973262

Another issue that would help with this is #1199866: Add an in-memory LRU cache.

@catch, I was thinking that a generic resetCache() call would also take care of the revision cache (when we'll have it), but that will probably use the same entity.memory_cache service so we should be fine with a more targeted approach. I tested this new patch in the same scenario as #8 and got the same results, the memory leak is fixed.

Committed/pushed to 8.8.x, and cherry-picked to 8.7.x, thanks!

double post

I just realised that #3055443: Switch to a null backend for all caches for running the database updates (which I just committed), renders this issue a bit moot. However I think we should probably leave it as is, since the code could potentially be used outside an update (like a drush command or similar), and because I didn't backport the other patch to 8.7

Didn't mean to change the status, leaving fixed.