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 float|null Minimum UNIX timestamp of 1+ expected startup positions */
47 protected $waitForPosTime;
48 /** @var int Max seconds to wait on positions to appear */
49 protected $waitForPosTimeout = self
::POS_WAIT_TIMEOUT
;
50 /** @var bool Whether to no-op all method calls */
51 protected $enabled = true;
52 /** @var bool Whether to check and wait on positions */
53 protected $wait = true;
55 /** @var bool Whether the client data was loaded */
56 protected $initialized = false;
57 /** @var DBMasterPos[] Map of (DB master name => position) */
58 protected $startupPositions = [];
59 /** @var DBMasterPos[] Map of (DB master name => position) */
60 protected $shutdownPositions = [];
61 /** @var float[] Map of (DB master name => 1) */
62 protected $shutdownTouchDBs = [];
64 /** @var integer Seconds to store positions */
65 const POSITION_TTL
= 60;
66 /** @var integer Max time to wait for positions to appear */
67 const POS_WAIT_TIMEOUT
= 5;
70 * @param BagOStuff $store
71 * @param array $client Map of (ip: <IP>, agent: <user-agent>)
72 * @param float $posTime UNIX timestamp
75 public function __construct( BagOStuff
$store, array $client, $posTime = null ) {
76 $this->store
= $store;
77 $this->clientId
= md5( $client['ip'] . "\n" . $client['agent'] );
78 $this->key
= $store->makeGlobalKey( __CLASS__
, $this->clientId
);
79 $this->waitForPosTime
= $posTime;
80 $this->logger
= new NullLogger();
83 public function setLogger( LoggerInterface
$logger ) {
84 $this->logger
= $logger;
88 * @param bool $enabled Whether to no-op all method calls
91 public function setEnabled( $enabled ) {
92 $this->enabled
= $enabled;
96 * @param bool $enabled Whether to check and wait on positions
99 public function setWaitEnabled( $enabled ) {
100 $this->wait
= $enabled;
104 * Initialise a ILoadBalancer to give it appropriate chronology protection.
106 * If the stash has a previous master position recorded, this will try to
107 * make sure that the next query to a replica DB of that master will see changes up
108 * to that position by delaying execution. The delay may timeout and allow stale
109 * data if no non-lagged replica DBs are available.
111 * @param ILoadBalancer $lb
114 public function initLB( ILoadBalancer
$lb ) {
115 if ( !$this->enabled ||
$lb->getServerCount() <= 1 ) {
116 return; // non-replicated setup or disabled
119 $this->initPositions();
121 $masterName = $lb->getServerName( $lb->getWriterIndex() );
122 if ( !empty( $this->startupPositions
[$masterName] ) ) {
123 $pos = $this->startupPositions
[$masterName];
124 $this->logger
->info( __METHOD__
. ": LB for '$masterName' set to pos $pos\n" );
125 $lb->waitFor( $pos );
130 * Notify the ChronologyProtector that the ILoadBalancer is about to shut
131 * down. Saves replication positions.
133 * @param ILoadBalancer $lb
136 public function shutdownLB( ILoadBalancer
$lb ) {
137 if ( !$this->enabled
) {
138 return; // not enabled
139 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF
) ) {
140 // Only save the position if writes have been done on the connection
144 $masterName = $lb->getServerName( $lb->getWriterIndex() );
145 if ( $lb->getServerCount() > 1 ) {
146 $pos = $lb->getMasterPos();
147 $this->logger
->info( __METHOD__
. ": LB for '$masterName' has pos $pos\n" );
148 $this->shutdownPositions
[$masterName] = $pos;
150 $this->logger
->info( __METHOD__
. ": DB '$masterName' touched\n" );
152 $this->shutdownTouchDBs
[$masterName] = 1;
156 * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
157 * May commit chronology data to persistent storage.
159 * @param callable|null $workCallback Work to do instead of waiting on syncing positions
160 * @param string $mode One of (sync, async); whether to wait on remote datacenters
161 * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
163 public function shutdown( callable
$workCallback = null, $mode = 'sync' ) {
164 if ( !$this->enabled
) {
168 $store = $this->store
;
169 // Some callers might want to know if a user recently touched a DB.
170 // These writes do not need to block on all datacenters receiving them.
171 foreach ( $this->shutdownTouchDBs
as $dbName => $unused ) {
173 $this->getTouchedKey( $this->store
, $dbName ),
179 if ( !count( $this->shutdownPositions
) ) {
180 return []; // nothing to save
183 $this->logger
->info( __METHOD__
. ": saving master pos for " .
184 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
187 // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
188 // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
189 // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
190 if ( $store->lock( $this->key
, 3 ) ) {
191 if ( $workCallback ) {
192 // Let the store run the work before blocking on a replication sync barrier. By the
193 // time it's done with the work, the barrier should be fast if replication caught up.
194 $store->addBusyCallback( $workCallback );
198 self
::mergePositions( $store->get( $this->key
), $this->shutdownPositions
),
200 ( $mode === 'sync' ) ?
$store::WRITE_SYNC
: 0
202 $store->unlock( $this->key
);
208 $bouncedPositions = $this->shutdownPositions
;
209 // Raced out too many times or stash is down
210 $this->logger
->warning( __METHOD__
. ": failed to save master pos for " .
211 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
213 } elseif ( $mode === 'sync' &&
214 $store->getQoS( $store::ATTR_SYNCWRITES
) < $store::QOS_SYNCWRITES_BE
216 // Positions may not be in all datacenters, force LBFactory to play it safe
217 $this->logger
->info( __METHOD__
. ": store may not support synchronous writes." );
218 $bouncedPositions = $this->shutdownPositions
;
220 $bouncedPositions = [];
223 return $bouncedPositions;
227 * @param string $dbName DB master name (e.g. "db1052")
228 * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
231 public function getTouched( $dbName ) {
232 return $this->store
->get( $this->getTouchedKey( $this->store
, $dbName ) );
236 * @param BagOStuff $store
237 * @param string $dbName
240 private function getTouchedKey( BagOStuff
$store, $dbName ) {
241 return $store->makeGlobalKey( __CLASS__
, 'mtime', $this->clientId
, $dbName );
245 * Load in previous master positions for the client
247 protected function initPositions() {
248 if ( $this->initialized
) {
252 $this->initialized
= true;
254 // If there is an expectation to see master positions with a certain min
255 // timestamp, then block until they appear, or until a timeout is reached.
256 if ( $this->waitForPosTime
> 0.0 ) {
258 $loop = new WaitConditionLoop(
259 function () use ( &$data ) {
260 $data = $this->store
->get( $this->key
);
262 return ( self
::minPosTime( $data ) >= $this->waitForPosTime
)
263 ? WaitConditionLoop
::CONDITION_REACHED
264 : WaitConditionLoop
::CONDITION_CONTINUE
;
266 $this->waitForPosTimeout
268 $result = $loop->invoke();
269 $waitedMs = $loop->getLastWaitTime() * 1e3
;
271 if ( $result == $loop::CONDITION_REACHED
) {
272 $msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
273 $this->logger
->debug( $msg );
275 $msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
276 $this->logger
->info( $msg );
279 $data = $this->store
->get( $this->key
);
282 $this->startupPositions
= $data ?
$data['positions'] : [];
283 $this->logger
->info( __METHOD__
. ": key is {$this->key} (read)\n" );
285 $this->startupPositions
= [];
286 $this->logger
->info( __METHOD__
. ": key is {$this->key} (unread)\n" );
291 * @param array|bool $data
294 private static function minPosTime( $data ) {
295 if ( !isset( $data['positions'] ) ) {
300 foreach ( $data['positions'] as $pos ) {
301 /** @var DBMasterPos $pos */
302 $min = $min ?
min( $pos->asOfTime(), $min ) : $pos->asOfTime();
309 * @param array|bool $curValue
310 * @param DBMasterPos[] $shutdownPositions
313 private static function mergePositions( $curValue, array $shutdownPositions ) {
314 /** @var $curPositions DBMasterPos[] */
315 if ( $curValue === false ) {
316 $curPositions = $shutdownPositions;
318 $curPositions = $curValue['positions'];
319 // Use the newest positions for each DB master
320 foreach ( $shutdownPositions as $db => $pos ) {
321 if ( !isset( $curPositions[$db] )
322 ||
$pos->asOfTime() > $curPositions[$db]->asOfTime()
324 $curPositions[$db] = $pos;
329 return [ 'positions' => $curPositions ];