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 $clientInfo;
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
= 60;
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->clientInfo
= $client +
[ 'clientId' => '' ];
89 $this->logger
= new NullLogger();
92 public function setLogger( LoggerInterface
$logger ) {
93 $this->logger
= $logger;
97 * @return string Client ID hash
100 public function getClientId() {
101 return $this->clientId
;
105 * @param bool $enabled Whether to no-op all method calls
108 public function setEnabled( $enabled ) {
109 $this->enabled
= $enabled;
113 * @param bool $enabled Whether to check and wait on positions
116 public function setWaitEnabled( $enabled ) {
117 $this->wait
= $enabled;
121 * Initialise a ILoadBalancer to give it appropriate chronology protection.
123 * If the stash has a previous master position recorded, this will try to
124 * make sure that the next query to a replica DB of that master will see changes up
125 * to that position by delaying execution. The delay may timeout and allow stale
126 * data if no non-lagged replica DBs are available.
128 * @param ILoadBalancer $lb
131 public function initLB( ILoadBalancer
$lb ) {
132 if ( !$this->enabled ||
$lb->getServerCount() <= 1 ) {
133 return; // non-replicated setup or disabled
136 $this->initPositions();
138 $masterName = $lb->getServerName( $lb->getWriterIndex() );
140 isset( $this->startupPositions
[$masterName] ) &&
141 $this->startupPositions
[$masterName] instanceof DBMasterPos
143 $pos = $this->startupPositions
[$masterName];
144 $this->logger
->debug( __METHOD__
. ": LB for '$masterName' set to pos $pos\n" );
145 $lb->waitFor( $pos );
150 * Notify the ChronologyProtector that the ILoadBalancer is about to shut
151 * down. Saves replication positions.
153 * @param ILoadBalancer $lb
156 public function shutdownLB( ILoadBalancer
$lb ) {
157 if ( !$this->enabled
) {
158 return; // not enabled
159 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF
) ) {
160 // Only save the position if writes have been done on the connection
164 $masterName = $lb->getServerName( $lb->getWriterIndex() );
165 if ( $lb->getServerCount() > 1 ) {
166 $pos = $lb->getMasterPos();
168 $this->logger
->debug( __METHOD__
. ": LB for '$masterName' has pos $pos\n" );
169 $this->shutdownPositions
[$masterName] = $pos;
172 $this->logger
->debug( __METHOD__
. ": DB '$masterName' touched\n" );
174 $this->shutdownTouchDBs
[$masterName] = 1;
178 * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
179 * May commit chronology data to persistent storage.
181 * @param callable|null $workCallback Work to do instead of waiting on syncing positions
182 * @param string $mode One of (sync, async); whether to wait on remote datacenters
183 * @param int|null &$cpIndex DB position key write counter; incremented on update
184 * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
186 public function shutdown( callable
$workCallback = null, $mode = 'sync', &$cpIndex = null ) {
187 if ( !$this->enabled
) {
191 $store = $this->store
;
192 // Some callers might want to know if a user recently touched a DB.
193 // These writes do not need to block on all datacenters receiving them.
194 foreach ( $this->shutdownTouchDBs
as $dbName => $unused ) {
196 $this->getTouchedKey( $this->store
, $dbName ),
202 if ( !count( $this->shutdownPositions
) ) {
203 return []; // nothing to save
206 $this->logger
->debug( __METHOD__
. ": saving master pos for " .
207 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
210 // CP-protected writes should overwhelmingly go to the master datacenter, so use a
211 // DC-local lock to merge the values. Use a DC-local get() and a synchronous all-DC
212 // set(). This makes it possible for the BagOStuff class to write in parallel to all
213 // DCs with one RTT. The use of WRITE_SYNC avoids needing READ_LATEST for the get().
214 if ( $store->lock( $this->key
, 3 ) ) {
215 if ( $workCallback ) {
216 // Let the store run the work before blocking on a replication sync barrier.
217 // If replication caught up while the work finished, the barrier will be fast.
218 $store->addBusyCallback( $workCallback );
222 $this->mergePositions(
223 $store->get( $this->key
),
224 $this->shutdownPositions
,
228 ( $mode === 'sync' ) ?
$store::WRITE_SYNC
: 0
230 $store->unlock( $this->key
);
236 $cpIndex = null; // nothing saved
237 $bouncedPositions = $this->shutdownPositions
;
238 // Raced out too many times or stash is down
239 $this->logger
->warning( __METHOD__
. ": failed to save master pos for " .
240 implode( ', ', array_keys( $this->shutdownPositions
) ) . "\n"
242 } elseif ( $mode === 'sync' &&
243 $store->getQoS( $store::ATTR_SYNCWRITES
) < $store::QOS_SYNCWRITES_BE
245 // Positions may not be in all datacenters, force LBFactory to play it safe
246 $this->logger
->info( __METHOD__
. ": store may not support synchronous writes." );
247 $bouncedPositions = $this->shutdownPositions
;
249 $bouncedPositions = [];
252 return $bouncedPositions;
256 * @param string $dbName DB master name (e.g. "db1052")
257 * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
260 public function getTouched( $dbName ) {
261 return $this->store
->get( $this->getTouchedKey( $this->store
, $dbName ) );
265 * @param BagOStuff $store
266 * @param string $dbName
269 private function getTouchedKey( BagOStuff
$store, $dbName ) {
270 return $store->makeGlobalKey( __CLASS__
, 'mtime', $this->clientId
, $dbName );
274 * Load in previous master positions for the client
276 protected function initPositions() {
277 if ( $this->initialized
) {
281 $this->initialized
= true;
283 // If there is an expectation to see master positions from a certain write
284 // index or higher, then block until it appears, or until a timeout is reached.
285 // Since the write index restarts each time the key is created, it is possible that
286 // a lagged store has a matching key write index. However, in that case, it should
287 // already be expired and thus treated as non-existing, maintaining correctness.
288 if ( $this->waitForPosIndex
> 0 ) {
290 $indexReached = null; // highest index reached in the position store
291 $loop = new WaitConditionLoop(
292 function () use ( &$data, &$indexReached ) {
293 $data = $this->store
->get( $this->key
);
294 if ( !is_array( $data ) ) {
295 return WaitConditionLoop
::CONDITION_CONTINUE
; // not found yet
296 } elseif ( !isset( $data['writeIndex'] ) ) {
297 return WaitConditionLoop
::CONDITION_REACHED
; // b/c
299 $indexReached = max( $data['writeIndex'], $indexReached );
301 return ( $data['writeIndex'] >= $this->waitForPosIndex
)
302 ? WaitConditionLoop
::CONDITION_REACHED
303 : WaitConditionLoop
::CONDITION_CONTINUE
;
305 $this->waitForPosStoreTimeout
307 $result = $loop->invoke();
308 $waitedMs = $loop->getLastWaitTime() * 1e3
;
310 if ( $result == $loop::CONDITION_REACHED
) {
311 $this->logger
->debug(
312 __METHOD__
. ": expected and found position index.",
314 'cpPosIndex' => $this->waitForPosIndex
,
315 'waitTimeMs' => $waitedMs
316 ] +
$this->clientInfo
319 $this->logger
->warning(
320 __METHOD__
. ": expected but failed to find position index.",
322 'cpPosIndex' => $this->waitForPosIndex
,
323 'indexReached' => $indexReached,
324 'waitTimeMs' => $waitedMs
325 ] +
$this->clientInfo
329 $data = $this->store
->get( $this->key
);
332 $this->startupPositions
= $data ?
$data['positions'] : [];
333 $this->logger
->debug( __METHOD__
. ": key is {$this->key} (read)\n" );
335 $this->startupPositions
= [];
336 $this->logger
->debug( __METHOD__
. ": key is {$this->key} (unread)\n" );
341 * @param array|bool $curValue
342 * @param DBMasterPos[] $shutdownPositions
343 * @param int|null &$cpIndex
346 protected function mergePositions( $curValue, array $shutdownPositions, &$cpIndex = null ) {
347 /** @var DBMasterPos[] $curPositions */
348 $curPositions = $curValue['positions'] ??
[];
349 // Use the newest positions for each DB master
350 foreach ( $shutdownPositions as $db => $pos ) {
352 !isset( $curPositions[$db] ) ||
353 !( $curPositions[$db] instanceof DBMasterPos
) ||
354 $pos->asOfTime() > $curPositions[$db]->asOfTime()
356 $curPositions[$db] = $pos;
360 $cpIndex = $curValue['writeIndex'] ??
0;
363 'positions' => $curPositions,
364 'writeIndex' => ++
$cpIndex