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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 [43775] from the 5.0 branch to trunk.

Fixes #35667.


Built from https://develop.svn.wordpress.org/trunk@44129


git-svn-id: http://core.svn.wordpress.org/trunk@43959 1a063a9b-81f0-0310-95a4-ce76da25c4cd
This commit is contained in:
Gary Pendergast 2018-12-14 01:04:36 +00:00
parent b91caddc1d
commit 786eb29de1
2 changed files with 42 additions and 14 deletions
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52
wp-includes/class-wp-text-diff-renderer-table.php
View File

@ -55,6 +55,22 @@ class WP_Text_Diff_Renderer_Table extends Text_Diff_Renderer {
protected $compat_fields = array( '_show_split_view', 'inline_diff_renderer', '_diff_threshold' );
/**
* 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();
/**
* Constructor - Call parent constructor with params array.
*
@ -396,15 +412,11 @@ class WP_Text_Diff_Renderer_Table extends Text_Diff_Renderer {
if ( false === $final_pos ) { // This orig is paired with a blank final.
array_splice( $final_rows, $orig_pos, 0, -1 );
} elseif ( $final_pos < $orig_pos ) { // This orig's match is up a ways. Pad final with blank rows.
$diff_pos = $final_pos - $orig_pos;
while ( $diff_pos < 0 ) {
array_splice( $final_rows, $orig_pos, 0, $diff_pos++ );
}
$diff_array = range( -1, $final_pos - $orig_pos );
array_splice( $final_rows, $orig_pos, 0, $diff_array );
} elseif ( $final_pos > $orig_pos ) { // This orig's match is down a ways. Pad orig with blank rows.
$diff_pos = $orig_pos - $final_pos;
while ( $diff_pos < 0 ) {
array_splice( $orig_rows, $orig_pos, 0, $diff_pos++ );
}
$diff_array = range( -1, $orig_pos - $final_pos );
array_splice( $orig_rows, $orig_pos, 0, $diff_array );
}
}
@ -434,12 +446,28 @@ class WP_Text_Diff_Renderer_Table extends Text_Diff_Renderer {
* @return int
*/
public function compute_string_distance( $string1, $string2 ) {
// Vectors containing character frequency for all chars in each string
$chars1 = count_chars( $string1 );
$chars2 = count_chars( $string2 );
// 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 );
// 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 );
}
$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.
$difference = array_sum( array_map( array( $this, 'difference' ), $chars1, $chars2 ) );
$this->difference_cache[ $difference_key ] = array_sum( array_map( array( $this, 'difference' ), $chars1, $chars2 ) );
}
$difference = $this->difference_cache[ $difference_key ];
// $string1 has zero length? Odd. Give huge penalty by not dividing.
if ( ! $string1 ) {

2
wp-includes/version.php
View File

@ -13,7 +13,7 @@
*
* @global string $wp_version
*/
$wp_version = '5.1-alpha-44128';
$wp_version = '5.1-alpha-44129';
/**
* Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.