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<title>[44129] Revisions: Improve performance of `WP_Text_Diff_Renderer_Table`.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/44129">44129</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/44129","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>pento</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2018-12-14 01:03:51 +0000 (Fri, 14 Dec 2018)</dd>
</dl>
<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Revisions: Improve performance of `WP_Text_Diff_Renderer_Table`.
`WP_Text_Diff_Renderer_Table` is used to generate the diff view in revisions, but there were some cases that could cause it to take excessive amounts of time to run.
Some noteable cases include:
- When a large number of new lines were inserted in the middle of the post from one revision to the next.
- When both revisions contain >100 lines.
- When either revision contains a lot of long lines.
In one extreme test case, the diff view took over a minute to generate. With this change, it now takes less than a second.
Merges <a href="https://core.trac.wordpress.org/changeset/43775">[43775]</a> from the 5.0 branch to trunk.
Fixes <a href="https://core.trac.wordpress.org/ticket/35667">#35667</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesclasswptextdiffrenderertablephp">trunk/src/wp-includes/class-wp-text-diff-renderer-table.php</a></li>
</ul>
<h3>Property Changed</h3>
<ul>
<li><a href="#trunk">trunk/</a></li>
</ul>
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<h3>Diff</h3>
<span class="cx" style="display: block; padding: 0 10px">Index: trunk
</span><span class="cx" style="display: block; padding: 0 10px">===================================================================
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">--- trunk 2018-12-14 00:57:50 UTC (rev 44128)
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+++ trunk 2018-12-14 01:03:51 UTC (rev 44129)
</ins><a id="trunk"></a>
<div class="propset"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Property changes: trunk</h4>
<pre class="diff"><span>
</span></pre></div>
<a id="svnmergeinfo"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: svn:mergeinfo</h4></div>
<span class="cx" style="display: block; padding: 0 10px"> /branches/3.3:20543
</span><span class="cx" style="display: block; padding: 0 10px"> /branches/3.4:21757
</span><span class="cx" style="display: block; padding: 0 10px"> /branches/4.9:43557,43622
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-/branches/5.0:43681-43682,43684-43688,43719-43720,43723,43726-43727,43729-43731,43734-43744,43751-43754,43758,43761-43765,43767-43770,43772,43774
</del><span class="cx" style="display: block; padding: 0 10px">\ No newline at end of property
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+/branches/5.0:43681-43682,43684-43688,43719-43720,43723,43726-43727,43729-43731,43734-43744,43751-43754,43758,43761-43765,43767-43770,43772,43774-43775
</ins><span class="cx" style="display: block; padding: 0 10px">\ No newline at end of property
</span><a id="trunksrcwpincludesclasswptextdiffrenderertablephp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/class-wp-text-diff-renderer-table.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/class-wp-text-diff-renderer-table.php 2018-12-14 00:57:50 UTC (rev 44128)
+++ trunk/src/wp-includes/class-wp-text-diff-renderer-table.php 2018-12-14 01:03:51 UTC (rev 44129)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -56,6 +56,22 @@
</span><span class="cx" style="display: block; padding: 0 10px"> protected $compat_fields = array( '_show_split_view', 'inline_diff_renderer', '_diff_threshold' );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Caches the output of count_chars() in compute_string_distance()
+ *
+ * @var array
+ * @since 5.0.0
+ */
+ protected $count_cache = array();
+
+ /**
+ * Caches the difference calculation in compute_string_distance()
+ *
+ * @var array
+ * @since 5.0.0
+ */
+ protected $difference_cache = array();
+
+ /**
</ins><span class="cx" style="display: block; padding: 0 10px"> * Constructor - Call parent constructor with params array.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * This will set class properties based on the key value pairs in the array.
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -396,15 +412,11 @@
</span><span class="cx" style="display: block; padding: 0 10px"> if ( false === $final_pos ) { // This orig is paired with a blank final.
</span><span class="cx" style="display: block; padding: 0 10px"> array_splice( $final_rows, $orig_pos, 0, -1 );
</span><span class="cx" style="display: block; padding: 0 10px"> } elseif ( $final_pos < $orig_pos ) { // This orig's match is up a ways. Pad final with blank rows.
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $diff_pos = $final_pos - $orig_pos;
- while ( $diff_pos < 0 ) {
- array_splice( $final_rows, $orig_pos, 0, $diff_pos++ );
- }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $diff_array = range( -1, $final_pos - $orig_pos );
+ array_splice( $final_rows, $orig_pos, 0, $diff_array );
</ins><span class="cx" style="display: block; padding: 0 10px"> } elseif ( $final_pos > $orig_pos ) { // This orig's match is down a ways. Pad orig with blank rows.
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $diff_pos = $orig_pos - $final_pos;
- while ( $diff_pos < 0 ) {
- array_splice( $orig_rows, $orig_pos, 0, $diff_pos++ );
- }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $diff_array = range( -1, $orig_pos - $final_pos );
+ array_splice( $orig_rows, $orig_pos, 0, $diff_array );
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -434,13 +446,29 @@
</span><span class="cx" style="display: block; padding: 0 10px"> * @return int
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><span class="cx" style="display: block; padding: 0 10px"> public function compute_string_distance( $string1, $string2 ) {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- // Vectors containing character frequency for all chars in each string
- $chars1 = count_chars( $string1 );
- $chars2 = count_chars( $string2 );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // Use an md5 hash of the strings for a count cache, as it's fast to generate, and collisions aren't a concern.
+ $count_key1 = md5( $string1 );
+ $count_key2 = md5( $string2 );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- // L1-norm of difference vector.
- $difference = array_sum( array_map( array( $this, 'difference' ), $chars1, $chars2 ) );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // Cache vectors containing character frequency for all chars in each string.
+ if ( ! isset( $this->count_cache[ $count_key1 ] ) ) {
+ $this->count_cache[ $count_key1 ] = count_chars( $string1 );
+ }
+ if ( ! isset( $this->count_cache[ $count_key2 ] ) ) {
+ $this->count_cache[ $count_key2 ] = count_chars( $string2 );
+ }
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $chars1 = $this->count_cache[ $count_key1 ];
+ $chars2 = $this->count_cache[ $count_key2 ];
+
+ $difference_key = md5( implode( ',', $chars1 ) . ':' . implode( ',', $chars2 ) );
+ if ( ! isset( $this->difference_cache[ $difference_key ] ) ) {
+ // L1-norm of difference vector.
+ $this->difference_cache[ $difference_key ] = array_sum( array_map( array( $this, 'difference' ), $chars1, $chars2 ) );
+ }
+
+ $difference = $this->difference_cache[ $difference_key ];
+
</ins><span class="cx" style="display: block; padding: 0 10px"> // $string1 has zero length? Odd. Give huge penalty by not dividing.
</span><span class="cx" style="display: block; padding: 0 10px"> if ( ! $string1 ) {
</span><span class="cx" style="display: block; padding: 0 10px"> return $difference;
</span></span></pre>
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