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[mediawiki.git] / includes / externalstore / ExternalStoreDB.php
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1 <?php
2 /**
3 * External storage in SQL database.
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License along
16 * with this program; if not, write to the Free Software Foundation, Inc.,
17 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
18 * http://www.gnu.org/copyleft/gpl.html
20 * @file
23 /**
24 * DB accessable external objects.
26 * In this system, each store "location" maps to a database "cluster".
27 * The clusters must be defined in the normal LBFactory configuration.
29 * @ingroup ExternalStorage
31 class ExternalStoreDB extends ExternalStoreMedium {
32 /**
33 * The provided URL is in the form of DB://cluster/id
34 * or DB://cluster/id/itemid for concatened storage.
36 * @see ExternalStoreMedium::fetchFromURL()
38 public function fetchFromURL( $url ) {
39 list( $cluster, $id, $itemID ) = $this->parseURL( $url );
40 $ret = $this->fetchBlob( $cluster, $id, $itemID );
42 if ( $itemID !== false && $ret !== false ) {
43 return $ret->getItem( $itemID );
46 return $ret;
49 /**
50 * Fetch data from given external store URLs.
51 * The provided URLs are in the form of DB://cluster/id
52 * or DB://cluster/id/itemid for concatened storage.
54 * @param array $urls An array of external store URLs
55 * @return array A map from url to stored content. Failed results
56 * are not represented.
58 public function batchFetchFromURLs( array $urls ) {
59 $batched = $inverseUrlMap = array();
60 foreach ( $urls as $url ) {
61 list( $cluster, $id, $itemID ) = $this->parseURL( $url );
62 $batched[$cluster][$id][] = $itemID;
63 // false $itemID gets cast to int, but should be ok
64 // since we do === from the $itemID in $batched
65 $inverseUrlMap[$cluster][$id][$itemID] = $url;
67 $ret = array();
68 foreach ( $batched as $cluster => $batchByCluster ) {
69 $res = $this->batchFetchBlobs( $cluster, $batchByCluster );
70 /** @var HistoryBlob $blob */
71 foreach ( $res as $id => $blob ) {
72 foreach ( $batchByCluster[$id] as $itemID ) {
73 $url = $inverseUrlMap[$cluster][$id][$itemID];
74 if ( $itemID === false ) {
75 $ret[$url] = $blob;
76 } else {
77 $ret[$url] = $blob->getItem( $itemID );
83 return $ret;
86 /**
87 * @see ExternalStoreMedium::store()
89 public function store( $cluster, $data ) {
90 $dbw = $this->getMaster( $cluster );
91 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
92 $dbw->insert( $this->getTable( $dbw ),
93 array( 'blob_id' => $id, 'blob_text' => $data ),
94 __METHOD__ );
95 $id = $dbw->insertId();
96 if ( !$id ) {
97 throw new MWException( __METHOD__ . ': no insert ID' );
100 return "DB://$cluster/$id";
104 * Get a LoadBalancer for the specified cluster
106 * @param string $cluster Cluster name
107 * @return LoadBalancer
109 function getLoadBalancer( $cluster ) {
110 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
112 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
116 * Get a slave database connection for the specified cluster
118 * @param string $cluster Cluster name
119 * @return DatabaseBase
121 function getSlave( $cluster ) {
122 global $wgDefaultExternalStore;
124 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
125 $lb = $this->getLoadBalancer( $cluster );
127 if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
128 wfDebug( "read only external store\n" );
129 $lb->allowLagged( true );
130 } else {
131 wfDebug( "writable external store\n" );
134 $db = $lb->getConnection( DB_SLAVE, array(), $wiki );
135 $db->clearFlag( DBO_TRX ); // sanity
137 return $db;
141 * Get a master database connection for the specified cluster
143 * @param string $cluster Cluster name
144 * @return DatabaseBase
146 function getMaster( $cluster ) {
147 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
148 $lb = $this->getLoadBalancer( $cluster );
150 $db = $lb->getConnection( DB_MASTER, array(), $wiki );
151 $db->clearFlag( DBO_TRX ); // sanity
153 return $db;
157 * Get the 'blobs' table name for this database
159 * @param DatabaseBase $db
160 * @return string Table name ('blobs' by default)
162 function getTable( $db ) {
163 $table = $db->getLBInfo( 'blobs table' );
164 if ( is_null( $table ) ) {
165 $table = 'blobs';
168 return $table;
172 * Fetch a blob item out of the database; a cache of the last-loaded
173 * blob will be kept so that multiple loads out of a multi-item blob
174 * can avoid redundant database access and decompression.
175 * @param string $cluster
176 * @param string $id
177 * @param string $itemID
178 * @return mixed
179 * @private
181 function fetchBlob( $cluster, $id, $itemID ) {
183 * One-step cache variable to hold base blobs; operations that
184 * pull multiple revisions may often pull multiple times from
185 * the same blob. By keeping the last-used one open, we avoid
186 * redundant unserialization and decompression overhead.
188 static $externalBlobCache = array();
190 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
191 if ( isset( $externalBlobCache[$cacheID] ) ) {
192 wfDebugLog( 'ExternalStoreDB-cache',
193 "ExternalStoreDB::fetchBlob cache hit on $cacheID" );
195 return $externalBlobCache[$cacheID];
198 wfDebugLog( 'ExternalStoreDB-cache',
199 "ExternalStoreDB::fetchBlob cache miss on $cacheID" );
201 $dbr = $this->getSlave( $cluster );
202 $ret = $dbr->selectField( $this->getTable( $dbr ),
203 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
204 if ( $ret === false ) {
205 wfDebugLog( 'ExternalStoreDB',
206 "ExternalStoreDB::fetchBlob master fallback on $cacheID" );
207 // Try the master
208 $dbw = $this->getMaster( $cluster );
209 $ret = $dbw->selectField( $this->getTable( $dbw ),
210 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
211 if ( $ret === false ) {
212 wfDebugLog( 'ExternalStoreDB',
213 "ExternalStoreDB::fetchBlob master failed to find $cacheID" );
216 if ( $itemID !== false && $ret !== false ) {
217 // Unserialise object; caller extracts item
218 $ret = unserialize( $ret );
221 $externalBlobCache = array( $cacheID => $ret );
223 return $ret;
227 * Fetch multiple blob items out of the database
229 * @param string $cluster A cluster name valid for use with LBFactory
230 * @param array $ids A map from the blob_id's to look for to the requested itemIDs in the blobs
231 * @return array A map from the blob_id's requested to their content.
232 * Unlocated ids are not represented
234 function batchFetchBlobs( $cluster, array $ids ) {
235 $dbr = $this->getSlave( $cluster );
236 $res = $dbr->select( $this->getTable( $dbr ),
237 array( 'blob_id', 'blob_text' ), array( 'blob_id' => array_keys( $ids ) ), __METHOD__ );
238 $ret = array();
239 if ( $res !== false ) {
240 $this->mergeBatchResult( $ret, $ids, $res );
242 if ( $ids ) {
243 wfDebugLog( __CLASS__, __METHOD__ .
244 " master fallback on '$cluster' for: " .
245 implode( ',', array_keys( $ids ) ) );
246 // Try the master
247 $dbw = $this->getMaster( $cluster );
248 $res = $dbw->select( $this->getTable( $dbr ),
249 array( 'blob_id', 'blob_text' ),
250 array( 'blob_id' => array_keys( $ids ) ),
251 __METHOD__ );
252 if ( $res === false ) {
253 wfDebugLog( __CLASS__, __METHOD__ . " master failed on '$cluster'" );
254 } else {
255 $this->mergeBatchResult( $ret, $ids, $res );
258 if ( $ids ) {
259 wfDebugLog( __CLASS__, __METHOD__ .
260 " master on '$cluster' failed locating items: " .
261 implode( ',', array_keys( $ids ) ) );
264 return $ret;
268 * Helper function for self::batchFetchBlobs for merging master/slave results
269 * @param array &$ret Current self::batchFetchBlobs return value
270 * @param array &$ids Map from blob_id to requested itemIDs
271 * @param mixed $res DB result from DatabaseBase::select
273 private function mergeBatchResult( array &$ret, array &$ids, $res ) {
274 foreach ( $res as $row ) {
275 $id = $row->blob_id;
276 $itemIDs = $ids[$id];
277 unset( $ids[$id] ); // to track if everything is found
278 if ( count( $itemIDs ) === 1 && reset( $itemIDs ) === false ) {
279 // single result stored per blob
280 $ret[$id] = $row->blob_text;
281 } else {
282 // multi result stored per blob
283 $ret[$id] = unserialize( $row->blob_text );
289 * @param string $url
290 * @return array
292 protected function parseURL( $url ) {
293 $path = explode( '/', $url );
295 return array(
296 $path[2], // cluster
297 $path[3], // id
298 isset( $path[4] ) ? $path[4] : false // itemID