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In wp_insert_term(), clean up accidental duplicate terms after insert.

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In [30056], the UNIQUE index was removed from the 'slug' column of `wp_terms`.
While we have numerous checks in place to avoid the creation of unwanted
duplicate term+term_taxonomy pairs, it's possible that in certain edge cases -
such as during the lag caused by database replication, or a race condition
involving near-simultaneous creation of more than one term - we'll end up
unwittingly inserting two identical rows.

The current changeset minimizes this risk by introducing a failsafe mechanism
into `wp_insert_term()`. After a term and term_taxonomy are INSERTed, we check
to see whether the term just created is a duplicate of an existing term; if so,
we delete the new one and keep the old one. This prevents problems caused by
replication lag, because SELECT queries that take place after an INSERT will
hit the master database; it mitigates race conditions by enforcing that the
term that was created first (ie, the one with the lowest `term_id`) is
always the "canonical" one.

Props nacin, markjaquith.
See #22023, #5809.

git-svn-id: https://develop.svn.wordpress.org/trunk@30238 602fd350-edb4-49c9-b593-d223f7449a82
This commit is contained in:
Boone Gorges 2014-11-05 00:59:51 +00:00
parent 367b8e340e
commit 3f7051bf81
1 changed files with 18 additions and 0 deletions
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18
src/wp-includes/taxonomy.php
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@ -2902,6 +2902,24 @@ function wp_insert_term( $term, $taxonomy, $args = array() ) {
$wpdb->insert( $wpdb->term_taxonomy, compact( 'term_id', 'taxonomy', 'description', 'parent') + array( 'count' => 0 ) );
$tt_id = (int) $wpdb->insert_id;
/*
* Sanity check: if we just created a term with the same parent + taxonomy + slug but a higher term_id than
* an existing term, then we have unwittingly created a duplicate term. Delete the dupe, and use the term_id
* and term_taxonomy_id of the older term instead. Then return out of the function so that the "create" hooks
* are not fired.
*/
$duplicate_term = $wpdb->get_row( $wpdb->prepare( "SELECT t.term_id, tt.term_taxonomy_id FROM $wpdb->terms t INNER JOIN $wpdb->term_taxonomy tt ON ( tt.term_id = t.term_id ) WHERE t.slug = %s AND tt.parent = %d AND tt.taxonomy = %s AND t.term_id < %d AND tt.term_taxonomy_id != %d", $slug, $parent, $taxonomy, $term_id, $tt_id ) );
if ( $duplicate_term ) {
$wpdb->delete( $wpdb->terms, array( 'term_id' => $term_id ) );
$wpdb->delete( $wpdb->term_taxonomy, array( 'term_taxonomy_id' => $tt_id ) );
$term_id = (int) $duplicate_term->term_id;
$tt_id = (int) $duplicate_term->term_taxonomy_id;
clean_term_cache( $term_id, $taxonomy );
return array( 'term_id' => $term_id, 'term_taxonomy_id' => $tt_id );
}
/**
* Fires immediately after a new term is created, before the term cache is cleaned.
*