delete_metadata should only delete metadata cache entries with the value specified in $meta_value arg

[rahal.aboulfeth]

In some cases ( huge database ) , wp_delete_attachment caused a Fatal error related to available memory.

The investigation led me to delete_metadata and more precisely to this line :

<?php
$object_ids = $wpdb->get_col( $wpdb->prepare( "SELECT $type_column FROM $table WHERE meta_key = %s", $meta_key ) );

Which as you see, tries to get all the post that have a meta_key.. ( in my case, it was the thumbnail ) , theses posts were extracted to allow flushing their meta cache.

[rahal.aboulfeth]

patch fix

[Clorith]

I'm not sure your patch applies here, as it fires on the conditional that you've supplied delete_metadata with the $delete_all as true, and you are then meant to delete all entries with that key regardless of the meta_value.

I suspect it would probably make more sense to look into the logic of wp_delete_attachment here

[rahal.aboulfeth]

The $meta_value comment says : Metadata value. Must be serializable if non-scalar. If specified, only delete metadata entries with this value. Otherwise, delete all entries with the specified meta_key. Pass null, false`, or an empty string to skip this check. (For backward compatibility,it is not possible to pass an empty string to delete those entries with an empty string for a value.)

The $delete_all comment says : Optional, default is false. If true, delete matching metadata entries for all objects, ignoring the specified object_id. Otherwise, only delete matching metadata entries for the specified object_id.

If I understand correctly , the matching metadata applies to entries where both key and value match , and not only the key. The fact is, if we try using this call with the _thumbnail_id for example, will will certainly get consume all the memory with wpbd:get_col .

But I think we can use an other conditional to add "AND meta_value = %s" if the $meta_value is specified. what do you think?

[boonebgorges]

@rahal.aboulfeth Thanks for the ticket and for the patch.

Replying to Clorith:

I'm not sure your patch applies here, as it fires on the conditional that you've supplied delete_metadata with the $delete_all as true, and you are then meant to delete all entries with that key regardless of the meta_value.

I suspect it would probably make more sense to look into the logic of wp_delete_attachment here

I believe this is incorrect. The "all" in $delete_all refers to "all objects" rather than "all meta for a given object".

[boonebgorges]

In 36511:

In delete_metadata(), only invalidate cache for affected objects.

The $delete_all flag in delete_metadata() triggers cache invalidation for
multiple objects. Previously, invalidation took place for all objects matching
the $meta_key parameter, regardless of whether $meta_value was also set.
This resulted in overly aggressive invalidation.

Props rahal.aboulfeth.
Fixes #35797.