summaryrefslogtreecommitdiff
path: root/includes/BacklinkCache.php
blob: d17104f8730d973a796ec392cd51d582e4463617 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
<?php
/**
 * File for BacklinkCache class
 * @file
 */

/**
 * Class for fetching backlink lists, approximate backlink counts and
 * partitions. This is a shared cache.
 *
 * Instances of this class should typically be fetched with the method
 * $title->getBacklinkCache().
 *
 * Ideally you should only get your backlinks from here when you think
 * there is some advantage in caching them. Otherwise it's just a waste
 * of memory.
 *
 * Introduced by r47317
 *
 * @internal documentation reviewed on 18 Mar 2011 by hashar
 *
 * @author Tim Starling
 * @copyright © 2009, Tim Starling, Domas Mituzas
 * @copyright © 2010, Max Sem
 * @copyright © 2011, Antoine Musso
 */
class BacklinkCache {

	/**
	 * Multi dimensions array representing batches. Keys are:
	 *  > (string) links table name
	 *    > 'numRows' : Number of rows for this link table
	 *    > 'batches' : array( $start, $end )
	 *
	 * @see BacklinkCache::partitionResult()
	 *
	 * Cleared with BacklinkCache::clear()
	 */
	protected $partitionCache = array();

	/**
	 * Contains the whole links from a database result.
	 * This is raw data that will be partitioned in $partitionCache
	 *
	 * Initialized with BacklinkCache::getLinks()
	 * Cleared with BacklinkCache::clear()
	 */
	protected $fullResultCache = array();

	/**
	 * Local copy of a database object.
	 *
	 * Accessor: BacklinkCache::getDB()
	 * Mutator : BacklinkCache::setDB()
	 * Cleared with BacklinkCache::clear()
	 */
	protected $db;

	/**
	 * Local copy of a Title object
	 */
	protected $title;

	const CACHE_EXPIRY = 3600;

	/**
	 * Create a new BacklinkCache
	 * @param Title $title : Title object to create a backlink cache for.
	 */
	function __construct( $title ) {
		$this->title = $title;
	}

	/**
	 * Serialization handler, diasallows to serialize the database to prevent
	 * failures after this class is deserialized from cache with dead DB
	 * connection.
	 *
	 * @return array
	 */
	function __sleep() {
		return array( 'partitionCache', 'fullResultCache', 'title' );
	}

	/**
	 * Clear locally stored data and database object.
	 */
	public function clear() {
		$this->partitionCache = array();
		$this->fullResultCache = array();
		unset( $this->db );
	}

	/**
	 * Set the Database object to use
	 *
	 * @param $db DatabaseBase
	 */
	public function setDB( $db ) {
		$this->db = $db;
	}

	/**
	 * Get the slave connection to the database
	 * When non existing, will initialize the connection.
	 * @return Database object
	 */
	protected function getDB() {
		if ( !isset( $this->db ) ) {
			$this->db = wfGetDB( DB_SLAVE );
		}

		return $this->db;
	}

	/**
	 * Get the backlinks for a given table. Cached in process memory only.
	 * @param $table String
	 * @param $startId Integer or false
	 * @param $endId Integer or false
	 * @return TitleArrayFromResult
	 */
	public function getLinks( $table, $startId = false, $endId = false ) {
		wfProfileIn( __METHOD__ );

		$fromField = $this->getPrefix( $table ) . '_from';

		if ( $startId || $endId ) {
			// Partial range, not cached
			wfDebug( __METHOD__ . ": from DB (uncacheable range)\n" );
			$conds = $this->getConditions( $table );

			// Use the from field in the condition rather than the joined page_id,
			// because databases are stupid and don't necessarily propagate indexes.
			if ( $startId ) {
				$conds[] = "$fromField >= " . intval( $startId );
			}

			if ( $endId ) {
				$conds[] = "$fromField <= " . intval( $endId );
			}

			$res = $this->getDB()->select(
				array( $table, 'page' ),
				array( 'page_namespace', 'page_title', 'page_id' ),
				$conds,
				__METHOD__,
				array(
					'STRAIGHT_JOIN',
					'ORDER BY' => $fromField
				) );
			$ta = TitleArray::newFromResult( $res );

			wfProfileOut( __METHOD__ );
			return $ta;
		}

		// @todo FIXME: Make this a function?
		if ( !isset( $this->fullResultCache[$table] ) ) {
			wfDebug( __METHOD__ . ": from DB\n" );
			$res = $this->getDB()->select(
				array( $table, 'page' ),
				array( 'page_namespace', 'page_title', 'page_id' ),
				$this->getConditions( $table ),
				__METHOD__,
				array(
					'STRAIGHT_JOIN',
					'ORDER BY' => $fromField,
				) );
			$this->fullResultCache[$table] = $res;
		}

		$ta = TitleArray::newFromResult( $this->fullResultCache[$table] );

		wfProfileOut( __METHOD__ );
		return $ta;
	}

	/**
	 * Get the field name prefix for a given table
	 * @param $table String
	 */
	protected function getPrefix( $table ) {
		static $prefixes = array(
			'pagelinks'     => 'pl',
			'imagelinks'    => 'il',
			'categorylinks' => 'cl',
			'templatelinks' => 'tl',
			'redirect'      => 'rd',
		);

		if ( isset( $prefixes[$table] ) ) {
			return $prefixes[$table];
		} else {
			$prefix = null;
			wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$prefix ) );
			if( $prefix ) {
				return $prefix;
			} else {
				throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
			}
		}
	}

	/**
	 * Get the SQL condition array for selecting backlinks, with a join
	 * on the page table.
	 * @param $table String
	 */
	protected function getConditions( $table ) {
		$prefix = $this->getPrefix( $table );

		// @todo FIXME: imagelinks and categorylinks do not rely on getNamespace,
		// they could be moved up for nicer case statements
		switch ( $table ) {
			case 'pagelinks':
			case 'templatelinks':
				$conds = array(
					"{$prefix}_namespace" => $this->title->getNamespace(),
					"{$prefix}_title"     => $this->title->getDBkey(),
					"page_id={$prefix}_from"
				);
				break;
			case 'redirect':
				$conds = array(
					"{$prefix}_namespace" => $this->title->getNamespace(),
					"{$prefix}_title"     => $this->title->getDBkey(),
					$this->getDb()->makeList( array(
						"{$prefix}_interwiki = ''",
						"{$prefix}_interwiki is null",
					), LIST_OR ),
					"page_id={$prefix}_from"
				);
				break;
			case 'imagelinks':
				$conds = array(
					'il_to' => $this->title->getDBkey(),
					'page_id=il_from'
				);
				break;
			case 'categorylinks':
				$conds = array(
					'cl_to' => $this->title->getDBkey(),
					'page_id=cl_from',
				);
				break;
			default:
				$conds = null;
				wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
				if( !$conds )
					throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
		}

		return $conds;
	}

	/**
	 * Get the approximate number of backlinks
	 * @param $table String
	 * @return integer
	 */
	public function getNumLinks( $table ) {
		if ( isset( $this->fullResultCache[$table] ) ) {
			return $this->fullResultCache[$table]->numRows();
		}

		if ( isset( $this->partitionCache[$table] ) ) {
			$entry = reset( $this->partitionCache[$table] );
			return $entry['numRows'];
		}

		$titleArray = $this->getLinks( $table );

		return $titleArray->count();
	}

	/**
	 * Partition the backlinks into batches.
	 * Returns an array giving the start and end of each range. The first
	 * batch has a start of false, and the last batch has an end of false.
	 *
	 * @param $table String: the links table name
	 * @param $batchSize Integer
	 * @return Array
	 */
	public function partition( $table, $batchSize ) {

		// 1) try partition cache ... 

		if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
			wfDebug( __METHOD__ . ": got from partition cache\n" );
			return $this->partitionCache[$table][$batchSize]['batches'];
		}

		$this->partitionCache[$table][$batchSize] = false;
		$cacheEntry =& $this->partitionCache[$table][$batchSize];

		// 2) ... then try full result cache ...

		if ( isset( $this->fullResultCache[$table] ) ) {
			$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
			wfDebug( __METHOD__ . ": got from full result cache\n" );

			return $cacheEntry['batches'];
		}

		// 3) ... fallback to memcached ...

		global $wgMemc;

		$memcKey = wfMemcKey(
			'backlinks',
			md5( $this->title->getPrefixedDBkey() ),
			$table,
			$batchSize
		);

		$memcValue = $wgMemc->get( $memcKey );

		if ( is_array( $memcValue ) ) {
			$cacheEntry = $memcValue;
			wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );

			return $cacheEntry['batches'];
		}


		// 4) ... finally fetch from the slow database :(

		$this->getLinks( $table );
		$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
		// Save to memcached
		$wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );

		wfDebug( __METHOD__ . ": got from database\n" );
		return $cacheEntry['batches'];
	}

	/**
	 * Partition a DB result with backlinks in it into batches
	 * @param $res ResultWrapper database result
	 * @param $batchSize integer
	 * @return array @see 
	 */
	protected function partitionResult( $res, $batchSize ) {
		$batches = array();
		$numRows = $res->numRows();
		$numBatches = ceil( $numRows / $batchSize );

		for ( $i = 0; $i < $numBatches; $i++ ) {
			if ( $i == 0  ) {
				$start = false;
			} else {
				$rowNum = intval( $numRows * $i / $numBatches );
				$res->seek( $rowNum );
				$row = $res->fetchObject();
				$start = $row->page_id;
			}

			if ( $i == $numBatches - 1 ) {
				$end = false;
			} else {
				$rowNum = intval( $numRows * ( $i + 1 ) / $numBatches );
				$res->seek( $rowNum );
				$row = $res->fetchObject();
				$end = $row->page_id - 1;
			}

			# Sanity check order
			if ( $start && $end && $start > $end ) {
				throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
			}

			$batches[] = array( $start, $end );
		}

		return array( 'numRows' => $numRows, 'batches' => $batches );
	}
}