3 * Generator of database load balancing objects.
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
24 namespace Wikimedia\Rdbms
;
26 use Psr\Log\LoggerAwareInterface
;
27 use Psr\Log\LoggerInterface
;
28 use Psr\Log\NullLogger
;
29 use Wikimedia\WaitConditionLoop
;
33 * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
34 * Kind of like Hawking's [[Chronology Protection Agency]].
36 class ChronologyProtector
implements LoggerAwareInterface
{
39 /** @var LoggerInterface */
42 /** @var string Storage key name */
44 /** @var string Hash of client parameters */
46 /** @var string[] Map of client information fields for logging */
47 protected $clientLogInfo;
48 /** @var int|null Expected minimum index of the last write to the position store */
49 protected $waitForPosIndex;
50 /** @var int Max seconds to wait on positions to appear */
51 protected $waitForPosStoreTimeout = self
::POS_STORE_WAIT_TIMEOUT
;
52 /** @var bool Whether to no-op all method calls */
53 protected $enabled = true;
54 /** @var bool Whether to check and wait on positions */
55 protected $wait = true;
57 /** @var bool Whether the client data was loaded */
58 protected $initialized = false;
59 /** @var DBMasterPos[] Map of (DB master name => position) */
60 protected $startupPositions = [];
61 /** @var DBMasterPos[] Map of (DB master name => position) */
62 protected $shutdownPositions = [];
63 /** @var float[] Map of (DB master name => 1) */
64 protected $shutdownTouchDBs = [];
66 /** @var int Seconds to store positions */
67 const POSITION_TTL
= 60;
68 /** @var int Seconds to store position write index cookies (safely less than POSITION_TTL) */
69 const POSITION_COOKIE_TTL
= 10;
70 /** @var int Max time to wait for positions to appear */
71 const POS_STORE_WAIT_TIMEOUT
= 5;
74 * @param BagOStuff $store
75 * @param array[] $client Map of (ip: <IP>, agent: <user-agent> [, clientId: <hash>] )
76 * @param int|null $posIndex Write counter index [optional]
79 public function __construct( BagOStuff
$store, array $client, $posIndex = null ) {
80 $this->store
= $store;
81 $this->clientId
= isset( $client['clientId'] )
83 : md5( $client['ip'] . "\n" . $client['agent'] );
84 $this->key
= $store->makeGlobalKey( __CLASS__
, $this->clientId
, 'v2' );
85 $this->waitForPosIndex
= $posIndex;
87 $this->clientLogInfo
= [
88 'clientIP' => $client['ip'],
89 'clientAgent' => $client['agent'],
90 'clientId' => $client['clientId'] ??
null
93 $this->logger
= new NullLogger();
96 public function setLogger( LoggerInterface
$logger ) {
97 $this->logger
= $logger;
101 * @return string Client ID hash
104 public function getClientId() {
105 return $this->clientId
;
109 * @param bool $enabled Whether to no-op all method calls
112 public function setEnabled( $enabled ) {
113 $this->enabled
= $enabled;
117 * @param bool $enabled Whether to check and wait on positions
120 public function setWaitEnabled( $enabled ) {
121 $this->wait
= $enabled;
125 * Initialise a ILoadBalancer to give it appropriate chronology protection.
127 * If the stash has a previous master position recorded, this will try to
128 * make sure that the next query to a replica DB of that master will see changes up
129 * to that position by delaying execution. The delay may timeout and allow stale
130 * data if no non-lagged replica DBs are available.
132 * @param ILoadBalancer $lb
135 public function initLB( ILoadBalancer
$lb ) {
136 if ( !$this->enabled ||
$lb->getServerCount() <= 1 ) {
137 return; // non-replicated setup or disabled
140 $this->initPositions();
142 $masterName = $lb->getServerName( $lb->getWriterIndex() );
144 isset( $this->startupPositions
[$masterName] ) &&
145 $this->startupPositions
[$masterName] instanceof DBMasterPos
147 $pos = $this->startupPositions
[$masterName];
148 $this->logger
->debug( __METHOD__
. ": LB for '$masterName' set to pos $pos\n" );
149 $lb->waitFor( $pos );
154 * Notify the ChronologyProtector that the ILoadBalancer is about to shut
155 * down. Saves replication positions.
157 * @param ILoadBalancer $lb
160 public function shutdownLB( ILoadBalancer
$lb ) {
161 if ( !$this->enabled
) {
162 return; // not enabled
163 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF
) ) {
164 // Only save the position if writes have been done on the connection
168 $masterName = $lb->getServerName( $lb->getWriterIndex() );
169 if ( $lb->getServerCount() > 1 ) {
170 $pos = $lb->getMasterPos();
172 $this->logger
->debug( __METHOD__
. ": LB for '$masterName' has pos $pos\n" );
173 $this->shutdownPositions
[$masterName] = $pos;
176 $this->logger
->debug( __METHOD__
. ": DB '$masterName' touched\n" );
178 $this->shutdownTouchDBs
[$masterName] = 1;
182 * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
183 * May commit chronology data to persistent storage.
185 * @param callable|null $workCallback Work to do instead of waiting on syncing positions
186 * @param string $mode One of (sync, async); whether to wait on remote datacenters
187 * @param int|null &$cpIndex DB position key write counter; incremented on update
188 * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
190 public function shutdown( callable
$workCallback = null, $mode = 'sync', &$cpIndex = null ) {
191 if ( !$this->enabled
) {
195 $store = $this->store
;
196 // Some callers might want to know if a user recently touched a DB.
197 // These writes do not need to block on all datacenters receiving them.
198 foreach ( $this->shutdownTouchDBs
as $dbName => $unused ) {
200 $this->getTouchedKey( $this->store
, $dbName ),
206 if ( !count( $this->shutdownPositions
) ) {
207 return []; // nothing to save
210 $this->logger
->debug( __METHOD__
. ": saving master pos for " .
211 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
214 // CP-protected writes should overwhelmingly go to the master datacenter, so use a
215 // DC-local lock to merge the values. Use a DC-local get() and a synchronous all-DC
216 // set(). This makes it possible for the BagOStuff class to write in parallel to all
217 // DCs with one RTT. The use of WRITE_SYNC avoids needing READ_LATEST for the get().
218 if ( $store->lock( $this->key
, 3 ) ) {
219 if ( $workCallback ) {
220 // Let the store run the work before blocking on a replication sync barrier.
221 // If replication caught up while the work finished, the barrier will be fast.
222 $store->addBusyCallback( $workCallback );
226 $this->mergePositions(
227 $store->get( $this->key
),
228 $this->shutdownPositions
,
232 ( $mode === 'sync' ) ?
$store::WRITE_SYNC
: 0
234 $store->unlock( $this->key
);
240 $cpIndex = null; // nothing saved
241 $bouncedPositions = $this->shutdownPositions
;
242 // Raced out too many times or stash is down
243 $this->logger
->warning( __METHOD__
. ": failed to save master pos for " .
244 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
246 } elseif ( $mode === 'sync' &&
247 $store->getQoS( $store::ATTR_SYNCWRITES
) < $store::QOS_SYNCWRITES_BE
249 // Positions may not be in all datacenters, force LBFactory to play it safe
250 $this->logger
->info( __METHOD__
. ": store may not support synchronous writes." );
251 $bouncedPositions = $this->shutdownPositions
;
253 $bouncedPositions = [];
256 return $bouncedPositions;
260 * @param string $dbName DB master name (e.g. "db1052")
261 * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
264 public function getTouched( $dbName ) {
265 return $this->store
->get( $this->getTouchedKey( $this->store
, $dbName ) );
269 * @param BagOStuff $store
270 * @param string $dbName
273 private function getTouchedKey( BagOStuff
$store, $dbName ) {
274 return $store->makeGlobalKey( __CLASS__
, 'mtime', $this->clientId
, $dbName );
278 * Load in previous master positions for the client
280 protected function initPositions() {
281 if ( $this->initialized
) {
285 $this->initialized
= true;
287 // If there is an expectation to see master positions from a certain write
288 // index or higher, then block until it appears, or until a timeout is reached.
289 // Since the write index restarts each time the key is created, it is possible that
290 // a lagged store has a matching key write index. However, in that case, it should
291 // already be expired and thus treated as non-existing, maintaining correctness.
292 if ( $this->waitForPosIndex
> 0 ) {
294 $indexReached = null; // highest index reached in the position store
295 $loop = new WaitConditionLoop(
296 function () use ( &$data, &$indexReached ) {
297 $data = $this->store
->get( $this->key
);
298 if ( !is_array( $data ) ) {
299 return WaitConditionLoop
::CONDITION_CONTINUE
; // not found yet
300 } elseif ( !isset( $data['writeIndex'] ) ) {
301 return WaitConditionLoop
::CONDITION_REACHED
; // b/c
303 $indexReached = max( $data['writeIndex'], $indexReached );
305 return ( $data['writeIndex'] >= $this->waitForPosIndex
)
306 ? WaitConditionLoop
::CONDITION_REACHED
307 : WaitConditionLoop
::CONDITION_CONTINUE
;
309 $this->waitForPosStoreTimeout
311 $result = $loop->invoke();
312 $waitedMs = $loop->getLastWaitTime() * 1e3
;
314 if ( $result == $loop::CONDITION_REACHED
) {
315 $this->logger
->debug(
316 __METHOD__
. ": expected and found position index.",
318 'cpPosIndex' => $this->waitForPosIndex
,
319 'waitTimeMs' => $waitedMs
320 ] +
$this->clientLogInfo
323 $this->logger
->warning(
324 __METHOD__
. ": expected but failed to find position index.",
326 'cpPosIndex' => $this->waitForPosIndex
,
327 'indexReached' => $indexReached,
328 'waitTimeMs' => $waitedMs
329 ] +
$this->clientLogInfo
333 $data = $this->store
->get( $this->key
);
336 $this->startupPositions
= $data ?
$data['positions'] : [];
337 $this->logger
->debug( __METHOD__
. ": key is {$this->key} (read)\n" );
339 $this->startupPositions
= [];
340 $this->logger
->debug( __METHOD__
. ": key is {$this->key} (unread)\n" );
345 * @param array|bool $curValue
346 * @param DBMasterPos[] $shutdownPositions
347 * @param int|null &$cpIndex
350 protected function mergePositions( $curValue, array $shutdownPositions, &$cpIndex = null ) {
351 /** @var DBMasterPos[] $curPositions */
352 $curPositions = $curValue['positions'] ??
[];
353 // Use the newest positions for each DB master
354 foreach ( $shutdownPositions as $db => $pos ) {
356 !isset( $curPositions[$db] ) ||
357 !( $curPositions[$db] instanceof DBMasterPos
) ||
358 $pos->asOfTime() > $curPositions[$db]->asOfTime()
360 $curPositions[$db] = $pos;
364 $cpIndex = $curValue['writeIndex'] ??
0;
367 'positions' => $curPositions,
368 'writeIndex' => ++
$cpIndex