objectcache: add object segmentation support to BagOStuff

Use it for ApiStashEdit so that large PaserOutput can be stored.

Add flag to allow for value segmentation on set() in BagOStuff.
Also add a flag for immediate deletion of segments on delete().

BagOStuff now has base serialize()/unserialize() methods.

Bug: T204742
Change-Id: I0667a02612526d8ddfd91d5de48b6faa78bd1ab5

autoload.php

@@ -1320,6 +1320,7 @@ $wgAutoloadLocalClasses = [
 	'SearchUpdate' => __DIR__ . '/includes/deferred/SearchUpdate.php',
 	'SectionProfileCallback' => __DIR__ . '/includes/profiler/SectionProfileCallback.php',
 	'SectionProfiler' => __DIR__ . '/includes/profiler/SectionProfiler.php',
+	'SerializedValueContainer' => __DIR__ . '/includes/libs/objectcache/serialized/SerializedValueContainer.php',
 	'SevenZipStream' => __DIR__ . '/maintenance/includes/SevenZipStream.php',
 	'ShiConverter' => __DIR__ . '/languages/classes/LanguageShi.php',
 	'ShortPagesPage' => __DIR__ . '/includes/specials/SpecialShortpages.php',

includes/Storage/PageEditStash.php

@@ -338,7 +338,12 @@ class PageEditStash {
 	public function stashInputText( $text, $textHash ) {
 		$textKey = $this->cache->makeKey( 'stashedit', 'text', $textHash );
 
-		return $this->cache->set( $textKey, $text, self::MAX_CACHE_TTL );
+		return $this->cache->set(
+			$textKey,
+			$text,
+			self::MAX_CACHE_TTL,
+			BagOStuff::WRITE_ALLOW_SEGMENTS
+		);
 	}
 
 	/**
@@ -388,7 +393,7 @@ class PageEditStash {
 	 */
 	private function getStashKey( Title $title, $contentHash, User $user ) {
 		return $this->cache->makeKey(
-			'stashed-edit-info',
+			'stashedit-info-v1',
 			md5( $title->getPrefixedDBkey() ),
 			// Account for the edit model/text
 			$contentHash,
@@ -397,29 +402,13 @@ class PageEditStash {
 		);
 	}
 
-	/**
-	 * @param string $hash
-	 * @return string
-	 */
-	private function getStashParserOutputKey( $hash ) {
-		return $this->cache->makeKey( 'stashed-edit-output', $hash );
-	}
-
 	/**
 	 * @param string $key
 	 * @return stdClass|bool Object map (pstContent,output,outputID,timestamp,edits) or false
 	 */
 	private function getStashValue( $key ) {
 		$stashInfo = $this->cache->get( $key );
-		if ( !is_object( $stashInfo ) ) {
+		if ( is_object( $stashInfo ) && $stashInfo->output instanceof ParserOutput ) {
-			return false;
-		}
-
-		$parserOutputKey = $this->getStashParserOutputKey( $stashInfo->outputID );
-		$parserOutput = $this->cache->get( $parserOutputKey );
-		if ( $parserOutput instanceof ParserOutput ) {
-			$stashInfo->output = $parserOutput;
-
 			return $stashInfo;
 		}
 
@@ -459,23 +448,14 @@ class PageEditStash {
 		}
 
 		// Store what is actually needed and split the output into another key (T204742)
-		$parserOutputID = md5( $key );
 		$stashInfo = (object)[
 			'pstContent' => $pstContent,
-			'outputID'   => $parserOutputID,
+			'output'     => $parserOutput,
 			'timestamp'  => $timestamp,
 			'edits'      => $user->getEditCount()
 		];
 
-		$ok = $this->cache->set( $key, $stashInfo, $ttl );
+		$ok = $this->cache->set( $key, $stashInfo, $ttl, BagOStuff::WRITE_ALLOW_SEGMENTS );
-		if ( $ok ) {
-			$ok = $this->cache->set(
-				$this->getStashParserOutputKey( $parserOutputID ),
-				$parserOutput,
-				$ttl
-			);
-		}
-
 		if ( $ok ) {
 			// These blobs can waste slots in low cardinality memcached slabs
 			$this->pruneExcessStashedEntries( $user, $key );
@@ -494,7 +474,7 @@ class PageEditStash {
 		$keyList = $this->cache->get( $key ) ?: [];
 		if ( count( $keyList ) >= self::MAX_CACHE_RECENT ) {
 			$oldestKey = array_shift( $keyList );
-			$this->cache->delete( $oldestKey );
+			$this->cache->delete( $oldestKey, BagOStuff::WRITE_PRUNE_SEGMENTS );
 		}
 
 		$keyList[] = $newKey;

includes/libs/objectcache/APCBagOStuff.php

@@ -45,6 +45,7 @@ class APCBagOStuff extends BagOStuff {
 	const KEY_SUFFIX = ':4';
 
 	public function __construct( array $params = [] ) {
+		$params['segmentationSize'] = $params['segmentationSize'] ?? INF;
 		parent::__construct( $params );
 		// The extension serializer is still buggy, unlike "php" and "igbinary"
 		$this->nativeSerialize = ( ini_get( 'apc.serializer' ) !== 'default' );
@@ -62,7 +63,7 @@ class APCBagOStuff extends BagOStuff {
 		return $value;
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 		apc_store(
 			$key . self::KEY_SUFFIX,
 			$this->nativeSerialize ? $value : $this->serialize( $value ),
@@ -80,7 +81,7 @@ class APCBagOStuff extends BagOStuff {
 		);
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		apc_delete( $key . self::KEY_SUFFIX );
 
 		return true;
@@ -93,12 +94,4 @@ class APCBagOStuff extends BagOStuff {
 	public function decr( $key, $value = 1 ) {
 		return apc_dec( $key . self::KEY_SUFFIX, $value );
 	}
-
-	protected function serialize( $value ) {
-		return $this->isInteger( $value ) ? (int)$value : serialize( $value );
-	}
-
-	protected function unserialize( $value ) {
-		return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
-	}
 }

includes/libs/objectcache/APCUBagOStuff.php

@@ -45,6 +45,7 @@ class APCUBagOStuff extends BagOStuff {
 	const KEY_SUFFIX = ':4';
 
 	public function __construct( array $params = [] ) {
+		$params['segmentationSize'] = $params['segmentationSize'] ?? INF;
 		parent::__construct( $params );
 		// The extension serializer is still buggy, unlike "php" and "igbinary"
 		$this->nativeSerialize = ( ini_get( 'apc.serializer' ) !== 'default' );
@@ -54,7 +55,7 @@ class APCUBagOStuff extends BagOStuff {
 		$casToken = null;
 
 		$blob = apcu_fetch( $key . self::KEY_SUFFIX );
-		$value = $this->unserialize( $blob );
+		$value = $this->nativeSerialize ? $blob : $this->unserialize( $blob );
 		if ( $value !== false ) {
 			$casToken = $blob; // don't bother hashing this
 		}
@@ -62,10 +63,10 @@ class APCUBagOStuff extends BagOStuff {
 		return $value;
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 		return apcu_store(
 			$key . self::KEY_SUFFIX,
-			$this->serialize( $value ),
+			$this->nativeSerialize ? $value : $this->serialize( $value ),
 			$exptime
 		);
 	}
@@ -73,12 +74,12 @@ class APCUBagOStuff extends BagOStuff {
 	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 		return apcu_add(
 			$key . self::KEY_SUFFIX,
-			$this->serialize( $value ),
+			$this->nativeSerialize ? $value : $this->serialize( $value ),
 			$exptime
 		);
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		apcu_delete( $key . self::KEY_SUFFIX );
 
 		return true;
@@ -101,20 +102,4 @@ class APCUBagOStuff extends BagOStuff {
 			return false;
 		}
 	}
-
-	protected function serialize( $value ) {
-		if ( $this->nativeSerialize ) {
-			return $value;
-		}
-
-		return $this->isInteger( $value ) ? (int)$value : serialize( $value );
-	}
-
-	protected function unserialize( $value ) {
-		if ( $this->nativeSerialize ) {
-			return $value;
-		}
-
-		return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
-	}
 }

includes/libs/objectcache/BagOStuff.php

@@ -50,8 +50,14 @@ use Wikimedia\WaitConditionLoop;
  * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
  * should semantically operate over its entire access scope; any nodes/threads in that scope
  * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
- * from one node in its access scope should reflect the prior changes of any other node its access
+ * from one node in its access scope should reflect the prior changes of any other node its
- * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
+ * access scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
+ *
+ * Subclasses should override the default "segmentationSize" field with an appropriate value.
+ * The value should not be larger than what the storage backend (by default) supports. It also
+ * should be roughly informed by common performance bottlenecks (e.g. values over a certain size
+ * having poor scalability). The same goes for the "segmentedValueMaxSize" member, which limits
+ * the maximum size and chunk count (indirectly) of values.
  *
  * @ingroup Cache
  */
@@ -68,6 +74,10 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	protected $asyncHandler;
 	/** @var int Seconds */
 	protected $syncTimeout;
+	/** @var int Bytes; chunk size of segmented cache values */
+	protected $segmentationSize;
+	/** @var int Bytes; maximum total size of a segmented cache value */
+	protected $segmentedValueMaxSize;
 
 	/** @var bool */
 	private $debugMode = false;
@@ -93,6 +103,11 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	/** Bitfield constants for set()/merge() */
 	const WRITE_SYNC = 4; // synchronously write to all locations for replicated stores
 	const WRITE_CACHE_ONLY = 8; // Only change state of the in-memory cache
+	const WRITE_ALLOW_SEGMENTS = 16; // Allow partitioning of the value if it is large
+	const WRITE_PRUNE_SEGMENTS = 32; // Delete all partition segments of the value
+
+	/** @var string Component to use for key construction of blob segment keys */
+	const SEGMENT_COMPONENT = 'segment';
 
 	/**
 	 * $params include:
@@ -103,6 +118,12 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 *   - reportDupes: Whether to emit warning log messages for all keys that were
 	 *      requested more than once (requires an asyncHandler).
 	 *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
+	 *   - segmentationSize: The chunk size, in bytes, of segmented values. The value should
+	 *      not exceed the maximum size of values in the storage backend, as configured by
+	 *      the site administrator.
+	 *   - segmentedValueMaxSize: The maximum total size, in bytes, of segmented values.
+	 *      This should be configured to a reasonable size give the site traffic and the
+	 *      amount of I/O between application and cache servers that the network can handle.
 	 * @param array $params
 	 */
 	public function __construct( array $params = [] ) {
@@ -119,6 +140,8 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 		}
 
 		$this->syncTimeout = $params['syncTimeout'] ?? 3;
+		$this->segmentationSize = $params['segmentationSize'] ?? 8388608; // 8MiB
+		$this->segmentedValueMaxSize = $params['segmentedValueMaxSize'] ?? 67108864; // 64MiB
 	}
 
 	/**
@@ -180,7 +203,7 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	public function get( $key, $flags = 0 ) {
 		$this->trackDuplicateKeys( $key );
 
-		return $this->doGet( $key, $flags );
+		return $this->resolveSegments( $key, $this->doGet( $key, $flags ) );
 	}
 
 	/**
@@ -233,7 +256,103 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 	 * @return bool Success
 	 */
-	abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
+	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+		if (
+			( $flags & self::WRITE_ALLOW_SEGMENTS ) != self::WRITE_ALLOW_SEGMENTS ||
+			is_infinite( $this->segmentationSize )
+		) {
+			return $this->doSet( $key, $value, $exptime, $flags );
+		}
+
+		$serialized = $this->serialize( $value );
+		$segmentSize = $this->getSegmentationSize();
+		$maxTotalSize = $this->getSegmentedValueMaxSize();
+
+		$size = strlen( $serialized );
+		if ( $size <= $segmentSize ) {
+			// Since the work of serializing it was already done, just use it inline
+			return $this->doSet(
+				$key,
+				SerializedValueContainer::newUnified( $serialized ),
+				$exptime,
+				$flags
+			);
+		} elseif ( $size > $maxTotalSize ) {
+			$this->setLastError( "Key $key exceeded $maxTotalSize bytes." );
+
+			return false;
+		}
+
+		$chunksByKey = [];
+		$segmentHashes = [];
+		$count = intdiv( $size, $segmentSize ) + ( ( $size % $segmentSize ) ? 1 : 0 );
+		for ( $i = 0; $i < $count; ++$i ) {
+			$segment = substr( $serialized, $i * $segmentSize, $segmentSize );
+			$hash = sha1( $segment );
+			$chunkKey = $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $hash );
+			$chunksByKey[$chunkKey] = $segment;
+			$segmentHashes[] = $hash;
+		}
+
+		$ok = $this->setMulti( $chunksByKey, $exptime, $flags );
+		if ( $ok ) {
+			// Only when all segments are stored should the main key be changed
+			$ok = $this->doSet(
+				$key,
+				SerializedValueContainer::newSegmented( $segmentHashes ),
+				$exptime,
+				$flags
+			);
+		}
+
+		return $ok;
+	}
+
+	/**
+	 * Set an item
+	 *
+	 * @param string $key
+	 * @param mixed $value
+	 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
+	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
+	 * @return bool Success
+	 */
+	abstract protected function doSet( $key, $value, $exptime = 0, $flags = 0 );
+
+	/**
+	 * Delete an item
+	 *
+	 * For large values written using WRITE_ALLOW_SEGMENTS, this only deletes the main
+	 * segment list key unless WRITE_PRUNE_SEGMENTS is in the flags. While deleting the segment
+	 * list key has the effect of functionally deleting the key, it leaves unused blobs in cache.
+	 *
+	 * @param string $key
+	 * @return bool True if the item was deleted or not found, false on failure
+	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
+	 */
+	public function delete( $key, $flags = 0 ) {
+		if ( ( $flags & self::WRITE_PRUNE_SEGMENTS ) != self::WRITE_PRUNE_SEGMENTS ) {
+			return $this->doDelete( $key, $flags );
+		}
+
+		$mainValue = $this->doGet( $key, self::READ_LATEST );
+		if ( !$this->doDelete( $key, $flags ) ) {
+			return false;
+		}
+
+		if ( !SerializedValueContainer::isSegmented( $mainValue ) ) {
+			return true; // no segments to delete
+		}
+
+		$orderedKeys = array_map(
+			function ( $segmentHash ) use ( $key ) {
+				return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
+			},
+			$mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
+		);
+
+		return $this->deleteMulti( $orderedKeys, $flags );
+	}
 
 	/**
 	 * Delete an item
@@ -242,7 +361,7 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @return bool True if the item was deleted or not found, false on failure
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 	 */
-	abstract public function delete( $key, $flags = 0 );
+	abstract protected function doDelete( $key, $flags = 0 );
 
 	/**
 	 * Insert an item if it does not already exist
@@ -291,7 +410,10 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 			$casToken = null; // passed by reference
 			// Get the old value and CAS token from cache
 			$this->clearLastError();
-			$currentValue = $this->doGet( $key, self::READ_LATEST, $casToken );
+			$currentValue = $this->resolveSegments(
+				$key,
+				$this->doGet( $key, self::READ_LATEST, $casToken )
+			);
 			if ( $this->getLastError() ) {
 				$this->logger->warning(
 					__METHOD__ . ' failed due to I/O error on get() for {key}.',
@@ -324,6 +446,7 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 
 				return false; // IO error; don't spam retries
 			}
+
 		} while ( !$success && --$attempts );
 
 		return $success;
@@ -338,7 +461,6 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 	 * @return bool Success
-	 * @throws Exception
 	 */
 	protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 		if ( !$this->lock( $key, 0 ) ) {
@@ -368,28 +490,40 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 *
 	 * If an expiry in the past is given then the key will immediately be expired
 	 *
+	 * For large values written using WRITE_ALLOW_SEGMENTS, this only changes the TTL of the
+	 * main segment list key. While lowering the TTL of the segment list key has the effect of
+	 * functionally lowering the TTL of the key, it might leave unused blobs in cache for longer.
+	 * Raising the TTL of such keys is not effective, since the expiration of a single segment
+	 * key effectively expires the entire value.
+	 *
 	 * @param string $key
-	 * @param int $expiry TTL or UNIX timestamp
+	 * @param int $exptime TTL or UNIX timestamp
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 	 * @return bool Success Returns false on failure or if the item does not exist
 	 * @since 1.28
 	 */
-	public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
+	public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
-		$found = false;
+		$expiry = $this->convertToExpiry( $exptime );
+		$delete = ( $expiry != 0 && $expiry < $this->getCurrentTime() );
 
-		$ok = $this->merge(
+		if ( !$this->lock( $key, 0 ) ) {
-			$key,
+			return false;
-			function ( $cache, $ttl, $currentValue ) use ( &$found ) {
+		}
-				$found = ( $currentValue !== false );
+		// Use doGet() to avoid having to trigger resolveSegments()
+		$blob = $this->doGet( $key, self::READ_LATEST );
+		if ( $blob ) {
+			if ( $delete ) {
+				$ok = $this->doDelete( $key, $flags );
+			} else {
+				$ok = $this->doSet( $key, $blob, $exptime, $flags );
+			}
+		} else {
+			$ok = false;
+		}
 
-				return $currentValue; // nothing is written if this is false
+		$this->unlock( $key );
-			},
-			$expiry,
-			1, // 1 attempt
-			$flags
-		);
 
-		return ( $ok && $found );
+		return $ok;
 	}
 
 	/**
@@ -459,7 +593,7 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 		if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 			unset( $this->locks[$key] );
 
-			$ok = $this->delete( "{$key}:lock" );
+			$ok = $this->doDelete( "{$key}:lock" );
 			if ( !$ok ) {
 				$this->logger->warning(
 					__METHOD__ . ' failed to release lock for {key}.',
@@ -533,9 +667,25 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @return array
 	 */
 	public function getMulti( array $keys, $flags = 0 ) {
+		$valuesBykey = $this->doGetMulti( $keys, $flags );
+		foreach ( $valuesBykey as $key => $value ) {
+			// Resolve one blob at a time (avoids too much I/O at once)
+			$valuesBykey[$key] = $this->resolveSegments( $key, $value );
+		}
+
+		return $valuesBykey;
+	}
+
+	/**
+	 * Get an associative array containing the item for each of the keys that have items.
+	 * @param string[] $keys List of keys
+	 * @param int $flags Bitfield; supports READ_LATEST [optional]
+	 * @return array
+	 */
+	protected function doGetMulti( array $keys, $flags = 0 ) {
 		$res = [];
 		foreach ( $keys as $key ) {
-			$val = $this->get( $key, $flags );
+			$val = $this->doGet( $key, $flags );
 			if ( $val !== false ) {
 				$res[$key] = $val;
 			}
@@ -546,6 +696,9 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 
 	/**
 	 * Batch insertion/replace
+	 *
+	 * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
+	 *
 	 * @param mixed[] $data Map of (key => value)
 	 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
@@ -553,11 +706,13 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @since 1.24
 	 */
 	public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
+		if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
+			throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
+		}
+
 		$res = true;
 		foreach ( $data as $key => $value ) {
-			if ( !$this->set( $key, $value, $exptime, $flags ) ) {
+			$res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
-				$res = false;
-			}
 		}
 
 		return $res;
@@ -565,6 +720,9 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 
 	/**
 	 * Batch deletion
+	 *
+	 * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
+	 *
 	 * @param string[] $keys List of keys
 	 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 	 * @return bool Success
@@ -573,7 +731,7 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	public function deleteMulti( array $keys, $flags = 0 ) {
 		$res = true;
 		foreach ( $keys as $key ) {
-			$res = $this->delete( $key, $flags ) && $res;
+			$res = $this->doDelete( $key, $flags ) && $res;
 		}
 
 		return $res;
@@ -624,6 +782,43 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 		return $newValue;
 	}
 
+	/**
+	 * Get and reassemble the chunks of blob at the given key
+	 *
+	 * @param string $key
+	 * @param mixed $mainValue
+	 * @return string|null|bool The combined string, false if missing, null on error
+	 */
+	protected function resolveSegments( $key, $mainValue ) {
+		if ( SerializedValueContainer::isUnified( $mainValue ) ) {
+			return $this->unserialize( $mainValue->{SerializedValueContainer::UNIFIED_DATA} );
+		}
+
+		if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
+			$orderedKeys = array_map(
+				function ( $segmentHash ) use ( $key ) {
+					return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
+				},
+				$mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
+			);
+
+			$segmentsByKey = $this->doGetMulti( $orderedKeys );
+
+			$parts = [];
+			foreach ( $orderedKeys as $segmentKey ) {
+				if ( isset( $segmentsByKey[$segmentKey] ) ) {
+					$parts[] = $segmentsByKey[$segmentKey];
+				} else {
+					return false; // missing segment
+				}
+			}
+
+			return $this->unserialize( implode( '', $parts ) );
+		}
+
+		return $mainValue;
+	}
+
 	/**
 	 * Get the "last error" registered; clearLastError() should be called manually
 	 * @return int ERR_* constant for the "last error" registry
@@ -732,7 +927,15 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	 * @return bool
 	 */
 	protected function isInteger( $value ) {
-		return ( is_int( $value ) || ctype_digit( $value ) );
+		if ( is_int( $value ) ) {
+			return true;
+		} elseif ( !is_string( $value ) ) {
+			return false;
+		}
+
+		$integer = (int)$value;
+
+		return ( $value === (string)$integer );
 	}
 
 	/**
@@ -784,6 +987,22 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 		return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 	}
 
+	/**
+	 * @return int|float The chunk size, in bytes, of segmented objects (INF for no limit)
+	 * @since 1.34
+	 */
+	public function getSegmentationSize() {
+		return $this->segmentationSize;
+	}
+
+	/**
+	 * @return int|float Maximum total segmented object size in bytes (INF for no limit)
+	 * @since 1.34
+	 */
+	public function getSegmentedValueMaxSize() {
+		return $this->segmentedValueMaxSize;
+	}
+
 	/**
 	 * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 	 *
@@ -820,4 +1039,22 @@ abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
 	public function setMockTime( &$time ) {
 		$this->wallClockOverride =& $time;
 	}
+
+	/**
+	 * @param mixed $value
+	 * @return string|int String/integer representation
+	 * @note Special handling is usually needed for integers so incr()/decr() work
+	 */
+	protected function serialize( $value ) {
+		return is_int( $value ) ? $value : serialize( $value );
+	}
+
+	/**
+	 * @param string|int $value
+	 * @return mixed Original value or false on error
+	 * @note Special handling is usually needed for integers so incr()/decr() work
+	 */
+	protected function unserialize( $value ) {
+		return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
+	}
 }

includes/libs/objectcache/EmptyBagOStuff.php

@@ -33,15 +33,15 @@ class EmptyBagOStuff extends BagOStuff {
 		return false;
 	}
 
-	public function add( $key, $value, $exp = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exp = 0, $flags = 0 ) {
 		return true;
 	}
 
-	public function set( $key, $value, $exp = 0, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		return true;
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 		return true;
 	}
 
@@ -49,6 +49,10 @@ class EmptyBagOStuff extends BagOStuff {
 		return false;
 	}
 
+	public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
+		return false; // faster
+	}
+
 	public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 		return true; // faster
 	}

includes/libs/objectcache/HashBagOStuff.php

@@ -49,6 +49,7 @@ class HashBagOStuff extends BagOStuff {
 	 *   - maxKeys : only allow this many keys (using oldest-first eviction)
 	 */
 	function __construct( $params = [] ) {
+		$params['segmentationSize'] = $params['segmentationSize'] ?? INF;
 		parent::__construct( $params );
 
 		$this->token = microtime( true ) . ':' . mt_rand();
@@ -75,7 +76,7 @@ class HashBagOStuff extends BagOStuff {
 		return $this->bag[$key][self::KEY_VAL];
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 		// Refresh key position for maxCacheKeys eviction
 		unset( $this->bag[$key] );
 		$this->bag[$key] = [
@@ -94,14 +95,14 @@ class HashBagOStuff extends BagOStuff {
 	}
 
 	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
-		if ( $this->get( $key ) === false ) {
+		if ( $this->hasKey( $key ) && !$this->expire( $key ) ) {
-			return $this->set( $key, $value, $exptime, $flags );
+			return false; // key already set
 		}
 
-		return false; // key already set
+		return $this->doSet( $key, $value, $exptime, $flags );
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		unset( $this->bag[$key] );
 
 		return true;
@@ -136,7 +137,7 @@ class HashBagOStuff extends BagOStuff {
 			return false;
 		}
 
-		$this->delete( $key );
+		$this->doDelete( $key );
 
 		return true;
 	}

includes/libs/objectcache/MemcachedBagOStuff.php

@@ -26,14 +26,12 @@
  *
  * @ingroup Cache
  */
-class MemcachedBagOStuff extends BagOStuff {
+abstract class MemcachedBagOStuff extends BagOStuff {
-	/** @var MemcachedClient|Memcached */
-	protected $client;
-
 	function __construct( array $params ) {
 		parent::__construct( $params );
 
 		$this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE; // unreliable
+		$this->segmentationSize = $params['maxPreferedKeySize'] ?? 917504; // < 1MiB
 	}
 
 	/**
@@ -50,55 +48,6 @@ class MemcachedBagOStuff extends BagOStuff {
 		];
 	}
 
-	protected function doGet( $key, $flags = 0, &$casToken = null ) {
-		return $this->client->get( $this->validateKeyEncoding( $key ), $casToken );
-	}
-
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
-		return $this->client->set( $this->validateKeyEncoding( $key ), $value,
-			$this->fixExpiry( $exptime ) );
-	}
-
-	protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
-		return $this->client->cas( $casToken, $this->validateKeyEncoding( $key ),
-			$value, $this->fixExpiry( $exptime ) );
-	}
-
-	public function delete( $key, $flags = 0 ) {
-		return $this->client->delete( $this->validateKeyEncoding( $key ) );
-	}
-
-	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
-		return $this->client->add( $this->validateKeyEncoding( $key ), $value,
-			$this->fixExpiry( $exptime ) );
-	}
-
-	public function incr( $key, $value = 1 ) {
-		$n = $this->client->incr( $this->validateKeyEncoding( $key ), $value );
-
-		return ( $n !== false && $n !== null ) ? $n : false;
-	}
-
-	public function decr( $key, $value = 1 ) {
-		$n = $this->client->decr( $this->validateKeyEncoding( $key ), $value );
-
-		return ( $n !== false && $n !== null ) ? $n : false;
-	}
-
-	public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
-		return $this->client->touch( $this->validateKeyEncoding( $key ),
-			$this->fixExpiry( $exptime ) );
-	}
-
-	/**
-	 * Get the underlying client object. This is provided for debugging
-	 * purposes.
-	 * @return MemcachedClient|Memcached
-	 */
-	public function getClient() {
-		return $this->client;
-	}
-
 	/**
 	 * Construct a cache key.
 	 *

includes/libs/objectcache/MemcachedClient.php

@@ -278,6 +278,23 @@ class MemcachedClient {
 	}
 
 	// }}}
+
+	/**
+	 * @param mixed $value
+	 * @return string|integer
+	 */
+	public function serialize( $value ) {
+		return serialize( $value );
+	}
+
+	/**
+	 * @param string $value
+	 * @return mixed
+	 */
+	public function unserialize( $value ) {
+		return unserialize( $value );
+	}
+
 	// {{{ add()
 
 	/**
@@ -503,7 +520,8 @@ class MemcachedClient {
 
 		if ( $this->_debug ) {
 			foreach ( $val as $k => $v ) {
-				$this->_debugprint( sprintf( "MemCache: sock %s got %s", serialize( $sock ), $k ) );
+				$this->_debugprint(
+					sprintf( "MemCache: sock %s got %s", $this->serialize( $sock ), $k ) );
 			}
 		}
 
@@ -1018,7 +1036,7 @@ class MemcachedClient {
 					 * yet read "END"), these 2 calls would collide.
 					 */
 					if ( $flags & self::SERIALIZED ) {
-						$ret[$rkey] = unserialize( $ret[$rkey] );
+						$ret[$rkey] = $this->unserialize( $ret[$rkey] );
 					} elseif ( $flags & self::INTVAL ) {
 						$ret[$rkey] = intval( $ret[$rkey] );
 					}
@@ -1072,7 +1090,7 @@ class MemcachedClient {
 		if ( is_int( $val ) ) {
 			$flags |= self::INTVAL;
 		} elseif ( !is_scalar( $val ) ) {
-			$val = serialize( $val );
+			$val = $this->serialize( $val );
 			$flags |= self::SERIALIZED;
 			if ( $this->_debug ) {
 				$this->_debugprint( sprintf( "client: serializing data as it is not scalar" ) );

includes/libs/objectcache/MemcachedPeclBagOStuff.php

@@ -27,6 +27,8 @@
  * @ingroup Cache
  */
 class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
+	/** @var Memcached */
+	protected $client;
 
 	/**
 	 * Available parameters are:
@@ -93,24 +95,22 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 		$this->client->setOption( Memcached::OPT_LIBKETAMA_COMPATIBLE, true );
 
 		// Set the serializer
-		switch ( $params['serializer'] ) {
+		$ok = false;
-			case 'php':
+		if ( $params['serializer'] === 'php' ) {
-				$this->client->setOption( Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_PHP );
+			$ok = $this->client->setOption( Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_PHP );
-				break;
+		} elseif ( $params['serializer'] === 'igbinary' ) {
-			case 'igbinary':
+			if ( !Memcached::HAVE_IGBINARY ) {
-				if ( !Memcached::HAVE_IGBINARY ) {
-					throw new InvalidArgumentException(
-						__CLASS__ . ': the igbinary extension is not available ' .
-						'but igbinary serialization was requested.'
-					);
-				}
-				$this->client->setOption( Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_IGBINARY );
-				break;
-			default:
 				throw new InvalidArgumentException(
-					__CLASS__ . ': invalid value for serializer parameter'
+					__CLASS__ . ': the igbinary extension is not available ' .
+					'but igbinary serialization was requested.'
 				);
+			}
+			$ok = $this->client->setOption( Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_IGBINARY );
 		}
+		if ( !$ok ) {
+			throw new InvalidArgumentException( __CLASS__ . ': invalid serializer parameter' );
+		}
+
 		$servers = [];
 		foreach ( $params['servers'] as $host ) {
 			if ( preg_match( '/^\[(.+)\]:(\d+)$/', $host, $m ) ) {
@@ -138,9 +138,6 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 		return $params;
 	}
 
-	/**
-	 * @suppress PhanTypeNonVarPassByRef
-	 */
 	protected function doGet( $key, $flags = 0, &$casToken = null ) {
 		$this->debug( "get($key)" );
 		if ( defined( Memcached::class . '::GET_EXTENDED' ) ) { // v3.0.0
@@ -160,9 +157,13 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 		return $result;
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 		$this->debug( "set($key)" );
-		$result = parent::set( $key, $value, $exptime, $flags = 0 );
+		$result = $this->client->set(
+			$this->validateKeyEncoding( $key ),
+			$value,
+			$this->fixExpiry( $exptime )
+		);
 		if ( $result === false && $this->client->getResultCode() === Memcached::RES_NOTSTORED ) {
 			// "Not stored" is always used as the mcrouter response with AllAsyncRoute
 			return true;
@@ -172,12 +173,14 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 
 	protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 		$this->debug( "cas($key)" );
-		return $this->checkResult( $key, parent::cas( $casToken, $key, $value, $exptime, $flags ) );
+		$result = $this->client->cas( $casToken, $this->validateKeyEncoding( $key ),
+			$value, $this->fixExpiry( $exptime ) );
+		return $this->checkResult( $key, $result );
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		$this->debug( "delete($key)" );
-		$result = parent::delete( $key );
+		$result = $this->client->delete( $this->validateKeyEncoding( $key ) );
 		if ( $result === false && $this->client->getResultCode() === Memcached::RES_NOTFOUND ) {
 			// "Not found" is counted as success in our interface
 			return true;
@@ -187,7 +190,12 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 
 	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 		$this->debug( "add($key)" );
-		return $this->checkResult( $key, parent::add( $key, $value, $exptime ) );
+		$result = $this->client->add(
+			$this->validateKeyEncoding( $key ),
+			$value,
+			$this->fixExpiry( $exptime )
+		);
+		return $this->checkResult( $key, $result );
 	}
 
 	public function incr( $key, $value = 1 ) {
@@ -242,7 +250,7 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 		return $result;
 	}
 
-	public function getMulti( array $keys, $flags = 0 ) {
+	public function doGetMulti( array $keys, $flags = 0 ) {
 		$this->debug( 'getMulti(' . implode( ', ', $keys ) . ')' );
 		foreach ( $keys as $key ) {
 			$this->validateKeyEncoding( $key );
@@ -260,9 +268,55 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 		return $this->checkResult( false, $result );
 	}
 
-	public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
+	public function deleteMulti( array $keys, $flags = 0 ) {
+		$this->debug( 'deleteMulti(' . implode( ', ', $keys ) . ')' );
+		foreach ( $keys as $key ) {
+			$this->validateKeyEncoding( $key );
+		}
+		$result = $this->client->deleteMulti( $keys ) ?: [];
+		$ok = true;
+		foreach ( $result as $code ) {
+			if ( !in_array( $code, [ true, Memcached::RES_NOTFOUND ], true ) ) {
+				// "Not found" is counted as success in our interface
+				$ok = false;
+			}
+		}
+		return $this->checkResult( false, $ok );
+	}
+
+	public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 		$this->debug( "touch($key)" );
-		$result = $this->client->touch( $key, $expiry );
+		$result = $this->client->touch( $key, $exptime );
 		return $this->checkResult( $key, $result );
 	}
+
+	protected function serialize( $value ) {
+		if ( is_int( $value ) ) {
+			return $value;
+		}
+
+		$serializer = $this->client->getOption( Memcached::OPT_SERIALIZER );
+		if ( $serializer === Memcached::SERIALIZER_PHP ) {
+			return serialize( $value );
+		} elseif ( $serializer === Memcached::SERIALIZER_IGBINARY ) {
+			return igbinary_serialize( $value );
+		}
+
+		throw new UnexpectedValueException( __METHOD__ . ": got serializer '$serializer'." );
+	}
+
+	protected function unserialize( $value ) {
+		if ( $this->isInteger( $value ) ) {
+			return (int)$value;
+		}
+
+		$serializer = $this->client->getOption( Memcached::OPT_SERIALIZER );
+		if ( $serializer === Memcached::SERIALIZER_PHP ) {
+			return unserialize( $value );
+		} elseif ( $serializer === Memcached::SERIALIZER_IGBINARY ) {
+			return igbinary_unserialize( $value );
+		}
+
+		throw new UnexpectedValueException( __METHOD__ . ": got serializer '$serializer'." );
+	}
 }

includes/libs/objectcache/MemcachedPhpBagOStuff.php

@@ -27,6 +27,9 @@
  * @ingroup Cache
  */
 class MemcachedPhpBagOStuff extends MemcachedBagOStuff {
+	/** @var MemcachedClient */
+	protected $client;
+
 	/**
 	 * Available parameters are:
 	 *   - servers:             The list of IP:port combinations holding the memcached servers.
@@ -51,11 +54,73 @@ class MemcachedPhpBagOStuff extends MemcachedBagOStuff {
 		$this->client->set_debug( $debug );
 	}
 
-	public function getMulti( array $keys, $flags = 0 ) {
+	protected function doGet( $key, $flags = 0, &$casToken = null ) {
+		$casToken = null;
+
+		return $this->client->get( $this->validateKeyEncoding( $key ), $casToken );
+	}
+
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
+		return $this->client->set(
+			$this->validateKeyEncoding( $key ),
+			$value,
+			$this->fixExpiry( $exptime )
+		);
+	}
+
+	protected function doDelete( $key, $flags = 0 ) {
+		return $this->client->delete( $this->validateKeyEncoding( $key ) );
+	}
+
+	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
+		return $this->client->add(
+			$this->validateKeyEncoding( $key ),
+			$value,
+			$this->fixExpiry( $exptime )
+		);
+	}
+
+	protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
+		return $this->client->cas(
+			$casToken,
+			$this->validateKeyEncoding( $key ),
+			$value,
+			$this->fixExpiry( $exptime )
+		);
+	}
+
+	public function incr( $key, $value = 1 ) {
+		$n = $this->client->incr( $this->validateKeyEncoding( $key ), $value );
+
+		return ( $n !== false && $n !== null ) ? $n : false;
+	}
+
+	public function decr( $key, $value = 1 ) {
+		$n = $this->client->decr( $this->validateKeyEncoding( $key ), $value );
+
+		return ( $n !== false && $n !== null ) ? $n : false;
+	}
+
+	public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
+		return $this->client->touch(
+			$this->validateKeyEncoding( $key ),
+			$this->fixExpiry( $exptime )
+		);
+	}
+
+	public function doGetMulti( array $keys, $flags = 0 ) {
 		foreach ( $keys as $key ) {
 			$this->validateKeyEncoding( $key );
 		}
 
 		return $this->client->get_multi( $keys );
 	}
+
+	protected function serialize( $value ) {
+		return is_int( $value ) ? $value : $this->client->serialize( $value );
+	}
+
+	protected function unserialize( $value ) {
+		return $this->isInteger( $value ) ? (int)$value : $this->client->unserialize( $value );
+	}
 }

includes/libs/objectcache/MultiWriteBagOStuff.php

@@ -130,6 +130,7 @@ class MultiWriteBagOStuff extends BagOStuff {
 				$missIndexes,
 				$this->asyncWrites,
 				'set',
+				// @TODO: consider using self::WRITE_ALLOW_SEGMENTS here?
 				[ $key, $value, self::UPGRADE_TTL ]
 			);
 		}
@@ -356,4 +357,24 @@ class MultiWriteBagOStuff extends BagOStuff {
 	protected function doGet( $key, $flags = 0, &$casToken = null ) {
 		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
 	}
+
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function doDelete( $key, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function doGetMulti( array $keys, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function serialize( $value ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function unserialize( $value ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
 }

includes/libs/objectcache/RESTBagOStuff.php

@@ -79,6 +79,7 @@ class RESTBagOStuff extends BagOStuff {
 	private $extendedErrorBodyFields;
 
 	public function __construct( $params ) {
+		$params['segmentationSize'] = $params['segmentationSize'] ?? INF;
 		if ( empty( $params['url'] ) ) {
 			throw new InvalidArgumentException( 'URL parameter is required' );
 		}
@@ -146,7 +147,7 @@ class RESTBagOStuff extends BagOStuff {
 		return false;
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 		// @TODO: respect WRITE_SYNC (e.g. EACH_QUORUM)
 		// @TODO: respect $exptime
 		$req = [
@@ -172,7 +173,7 @@ class RESTBagOStuff extends BagOStuff {
 		return false; // key already set
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		// @TODO: respect WRITE_SYNC (e.g. EACH_QUORUM)
 		$req = [
 			'method' => 'DELETE',

includes/libs/objectcache/RedisBagOStuff.php

@@ -106,7 +106,7 @@ class RedisBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	public function set( $key, $value, $expiry = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $expiry = 0, $flags = 0 ) {
 		list( $server, $conn ) = $this->getConnection( $key );
 		if ( !$conn ) {
 			return false;
@@ -128,7 +128,7 @@ class RedisBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		list( $server, $conn ) = $this->getConnection( $key );
 		if ( !$conn ) {
 			return false;
@@ -146,7 +146,7 @@ class RedisBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	public function getMulti( array $keys, $flags = 0 ) {
+	public function doGetMulti( array $keys, $flags = 0 ) {
 		$batches = [];
 		$conns = [];
 		foreach ( $keys as $key ) {
@@ -351,25 +351,6 @@ class RedisBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	/**
-	 * @param mixed $data
-	 * @return string
-	 */
-	protected function serialize( $data ) {
-		// Serialize anything but integers so INCR/DECR work
-		// Do not store integer-like strings as integers to avoid type confusion (T62563)
-		return is_int( $data ) ? $data : serialize( $data );
-	}
-
-	/**
-	 * @param string $data
-	 * @return mixed
-	 */
-	protected function unserialize( $data ) {
-		$int = intval( $data );
-		return $data === (string)$int ? $int : unserialize( $data );
-	}
-
 	/**
 	 * Get a Redis object with a connection suitable for fetching the specified key
 	 * @param string $key

includes/libs/objectcache/ReplicatedBagOStuff.php

@@ -75,7 +75,7 @@ class ReplicatedBagOStuff extends BagOStuff {
 	}
 
 	public function get( $key, $flags = 0 ) {
-		return ( $flags & self::READ_LATEST )
+		return ( ( $flags & self::READ_LATEST ) == self::READ_LATEST )
 			? $this->writeStore->get( $key, $flags )
 			: $this->readStore->get( $key, $flags );
 	}
@@ -164,4 +164,24 @@ class ReplicatedBagOStuff extends BagOStuff {
 	protected function doGet( $key, $flags = 0, &$casToken = null ) {
 		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
 	}
+
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function doDelete( $key, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function doGetMulti( array $keys, $flags = 0 ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function serialize( $value ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
+
+	protected function unserialize( $blob ) {
+		throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
+	}
 }

includes/libs/objectcache/WinCacheBagOStuff.php

@@ -36,7 +36,7 @@ class WinCacheBagOStuff extends BagOStuff {
 			return false;
 		}
 
-		$value = unserialize( $blob );
+		$value = $this->unserialize( $blob );
 		if ( $value !== false ) {
 			$casToken = (string)$blob; // don't bother hashing this
 		}
@@ -67,8 +67,8 @@ class WinCacheBagOStuff extends BagOStuff {
 		return $success;
 	}
 
-	public function set( $key, $value, $expire = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $expire = 0, $flags = 0 ) {
-		$result = wincache_ucache_set( $key, serialize( $value ), $expire );
+		$result = wincache_ucache_set( $key, $this->serialize( $value ), $expire );
 
 		// false positive, wincache_ucache_set returns an empty array
 		// in some circumstances.
@@ -77,7 +77,11 @@ class WinCacheBagOStuff extends BagOStuff {
 	}
 
 	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
-		$result = wincache_ucache_add( $key, serialize( $value ), $exptime );
+		if ( wincache_ucache_exists( $key ) ) {
+			return false; // avoid warnings
+		}
+
+		$result = wincache_ucache_add( $key, $this->serialize( $value ), $exptime );
 
 		// false positive, wincache_ucache_add returns an empty array
 		// in some circumstances.
@@ -85,7 +89,7 @@ class WinCacheBagOStuff extends BagOStuff {
 		return ( $result === [] || $result === true );
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
 		wincache_ucache_delete( $key );
 
 		return true;

includes/libs/objectcache/serialized/SerializedValueContainer.php

@@ -0,0 +1,66 @@
+<?php
+
+/**
+ * Helper class for segmenting large cache values without relying on serializing classes
+ *
+ * @since 1.34
+ */
+class SerializedValueContainer {
+	const SCHEMA = '__svc_schema__';
+	const SCHEMA_UNIFIED = 'DAAIDgoKAQw'; // 64 bit UID
+	const SCHEMA_SEGMENTED = 'CAYCDAgCDw4'; // 64 bit UID
+
+	const UNIFIED_DATA = '__data__';
+	const SEGMENTED_HASHES = '__hashes__';
+
+	/**
+	 * @param string $serialized
+	 * @return stdClass
+	 */
+	public static function newUnified( $serialized ) {
+		return (object)[
+			self::SCHEMA => self::SCHEMA_UNIFIED,
+			self::UNIFIED_DATA => $serialized
+		];
+	}
+
+	/**
+	 * @param string[] $segmentHashList Ordered list of hashes for each segment
+	 * @return stdClass
+	 */
+	public static function newSegmented( array $segmentHashList ) {
+		return (object)[
+			self::SCHEMA => self::SCHEMA_SEGMENTED,
+			self::SEGMENTED_HASHES => $segmentHashList
+		];
+	}
+
+	/**
+	 * @param mixed $value
+	 * @return bool
+	 */
+	public static function isUnified( $value ) {
+		return self::instanceOf( $value, self::SCHEMA_UNIFIED );
+	}
+
+	/**
+	 * @param mixed $value
+	 * @return bool
+	 */
+	public static function isSegmented( $value ) {
+		return self::instanceOf( $value, self::SCHEMA_SEGMENTED );
+	}
+
+	/**
+	 * @param mixed $value
+	 * @param string $schema SCHEMA_* class constant
+	 * @return bool
+	 */
+	private static function instanceOf( $value, $schema ) {
+		return (
+			$value instanceof stdClass &&
+			property_exists( $value, self::SCHEMA ) &&
+			$value->{self::SCHEMA} === $schema
+		);
+	}
+}

includes/objectcache/SqlBagOStuff.php

@@ -250,7 +250,7 @@ class SqlBagOStuff extends BagOStuff {
 		return false;
 	}
 
-	public function getMulti( array $keys, $flags = 0 ) {
+	protected function doGetMulti( array $keys, $flags = 0 ) {
 		$values = [];
 
 		$blobs = $this->fetchBlobMulti( $keys );
@@ -261,7 +261,7 @@ class SqlBagOStuff extends BagOStuff {
 		return $values;
 	}
 
-	public function fetchBlobMulti( array $keys, $flags = 0 ) {
+	protected function fetchBlobMulti( array $keys, $flags = 0 ) {
 		$values = []; // array of (key => value)
 
 		$keysByTable = [];
@@ -391,8 +391,8 @@ class SqlBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+	protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
-		$ok = $this->setMulti( [ $key => $value ], $exptime );
+		$ok = $this->insertMulti( [ $key => $value ], $exptime, $flags, true );
 
 		return $ok;
 	}
@@ -446,6 +446,10 @@ class SqlBagOStuff extends BagOStuff {
 	}
 
 	public function deleteMulti( array $keys, $flags = 0 ) {
+		return $this->purgeMulti( $keys, $flags );
+	}
+
+	public function purgeMulti( array $keys, $flags = 0 ) {
 		$keysByTable = [];
 		foreach ( $keys as $key ) {
 			list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
@@ -482,8 +486,8 @@ class SqlBagOStuff extends BagOStuff {
 		return $result;
 	}
 
-	public function delete( $key, $flags = 0 ) {
+	protected function doDelete( $key, $flags = 0 ) {
-		$ok = $this->deleteMulti( [ $key ], $flags );
+		$ok = $this->purgeMulti( [ $key ], $flags );
 
 		return $ok;
 	}
@@ -730,10 +734,10 @@ class SqlBagOStuff extends BagOStuff {
 	 * On typical message and page data, this can provide a 3X decrease
 	 * in storage requirements.
 	 *
-	 * @param mixed &$data
+	 * @param mixed $data
 	 * @return string
 	 */
-	protected function serialize( &$data ) {
+	protected function serialize( $data ) {
 		$serial = serialize( $data );
 
 		if ( function_exists( 'gzdeflate' ) ) {

tests/phpunit/includes/api/ApiStashEditTest.php

@@ -347,8 +347,6 @@ class ApiStashEditTest extends ApiTestCase {
 		$cache = $editStash->cache;
 
 		$editInfo = $cache->get( $key );
-		$outputKey = $cache->makeKey( 'stashed-edit-output', $editInfo->outputID );
-		$editInfo->output = $cache->get( $outputKey );
 		$editInfo->output->setCacheTime( wfTimestamp( TS_MW,
 			wfTimestamp( TS_UNIX, $editInfo->output->getCacheTime() ) - $howOld - 1 ) );
 

tests/phpunit/includes/libs/objectcache/BagOStuffTest.php

@@ -1,6 +1,7 @@
 <?php
 
 use Wikimedia\ScopedCallback;
+use Wikimedia\TestingAccessWrapper;
 
 /**
  * @author Matthias Mullie <mmullie@wikimedia.org>
@@ -98,13 +99,13 @@ class BagOStuffTest extends MediaWikiTestCase {
 			$this->cache->merge( $key, $callback, 5, 1 ),
 			'Non-blocking merge (CAS)'
 		);
+
 		if ( $this->cache instanceof MultiWriteBagOStuff ) {
-			$wrapper = \Wikimedia\TestingAccessWrapper::newFromObject( $this->cache );
+			$wrapper = TestingAccessWrapper::newFromObject( $this->cache );
-			$n = count( $wrapper->caches );
+			$this->assertEquals( count( $wrapper->caches ), $calls );
 		} else {
-			$n = 1;
+			$this->assertEquals( 1, $calls );
 		}
-		$this->assertEquals( $n, $calls );
 	}
 
 	/**
@@ -115,10 +116,17 @@ class BagOStuffTest extends MediaWikiTestCase {
 		$value = 'meow';
 
 		$this->cache->add( $key, $value, 5 );
-		$this->assertTrue( $this->cache->changeTTL( $key, 5 ) );
+		$this->assertEquals( $value, $this->cache->get( $key ) );
+		$this->assertTrue( $this->cache->changeTTL( $key, 10 ) );
+		$this->assertTrue( $this->cache->changeTTL( $key, 10 ) );
+		$this->assertTrue( $this->cache->changeTTL( $key, 0 ) );
 		$this->assertEquals( $this->cache->get( $key ), $value );
 		$this->cache->delete( $key );
-		$this->assertFalse( $this->cache->changeTTL( $key, 5 ) );
+		$this->assertFalse( $this->cache->changeTTL( $key, 15 ) );
+
+		$this->cache->add( $key, $value, 5 );
+		$this->assertTrue( $this->cache->changeTTL( $key, time() - 3600 ) );
+		$this->assertFalse( $this->cache->get( $key ) );
 	}
 
 	/**
@@ -126,7 +134,9 @@ class BagOStuffTest extends MediaWikiTestCase {
 	 */
 	public function testAdd() {
 		$key = $this->cache->makeKey( self::TEST_KEY );
+		$this->assertFalse( $this->cache->get( $key ) );
 		$this->assertTrue( $this->cache->add( $key, 'test', 5 ) );
+		$this->assertFalse( $this->cache->add( $key, 'test', 5 ) );
 	}
 
 	/**
@@ -237,20 +247,73 @@ class BagOStuffTest extends MediaWikiTestCase {
 			$this->cache->makeKey( 'test-6' ) => 'ever'
 		];
 
-		$this->cache->setMulti( $map, 5 );
+		$this->assertTrue( $this->cache->setMulti( $map ) );
 		$this->assertEquals(
 			$map,
 			$this->cache->getMulti( array_keys( $map ) )
 		);
 
-		$this->assertTrue( $this->cache->deleteMulti( array_keys( $map ), 5 ) );
+		$this->assertTrue( $this->cache->deleteMulti( array_keys( $map ) ) );
 
+		$this->assertEquals(
+			[],
+			$this->cache->getMulti( array_keys( $map ), BagOStuff::READ_LATEST )
+		);
 		$this->assertEquals(
 			[],
 			$this->cache->getMulti( array_keys( $map ) )
 		);
 	}
 
+	/**
+	 * @covers BagOStuff::get
+	 * @covers BagOStuff::getMulti
+	 * @covers BagOStuff::merge
+	 * @covers BagOStuff::delete
+	 */
+	public function testSetSegmentable() {
+		$key = $this->cache->makeKey( self::TEST_KEY );
+		$tiny = 418;
+		$small = wfRandomString( 32 );
+		// 64 * 8 * 32768 = 16777216 bytes
+		$big = str_repeat( wfRandomString( 32 ) . '-' . wfRandomString( 32 ), 32768 );
+
+		$callback = function ( $cache, $key, $oldValue ) {
+			return $oldValue . '!';
+		};
+
+		foreach ( [ $tiny, $small, $big ] as $value ) {
+			$this->cache->set( $key, $value, 10, BagOStuff::WRITE_ALLOW_SEGMENTS );
+			$this->assertEquals( $value, $this->cache->get( $key ) );
+			$this->assertEquals( $value, $this->cache->getMulti( [ $key ] )[$key] );
+
+			$this->assertTrue( $this->cache->merge( $key, $callback, 5 ) );
+			$this->assertEquals( "$value!", $this->cache->get( $key ) );
+			$this->assertEquals( "$value!", $this->cache->getMulti( [ $key ] )[$key] );
+
+			$this->assertTrue( $this->cache->deleteMulti( [ $key ] ) );
+			$this->assertFalse( $this->cache->get( $key ) );
+			$this->assertEquals( [], $this->cache->getMulti( [ $key ] ) );
+
+			$this->cache->set( $key, "@$value", 10, BagOStuff::WRITE_ALLOW_SEGMENTS );
+			$this->assertEquals( "@$value", $this->cache->get( $key ) );
+			$this->assertTrue( $this->cache->delete( $key, BagOStuff::WRITE_PRUNE_SEGMENTS ) );
+			$this->assertFalse( $this->cache->get( $key ) );
+			$this->assertEquals( [], $this->cache->getMulti( [ $key ] ) );
+		}
+
+		$this->cache->set( $key, 666, 10, BagOStuff::WRITE_ALLOW_SEGMENTS );
+
+		$this->assertEquals( 667, $this->cache->incr( $key ) );
+		$this->assertEquals( 667, $this->cache->get( $key ) );
+
+		$this->assertEquals( 664, $this->cache->decr( $key, 3 ) );
+		$this->assertEquals( 664, $this->cache->get( $key ) );
+
+		$this->assertTrue( $this->cache->delete( $key ) );
+		$this->assertFalse( $this->cache->get( $key ) );
+	}
+
 	/**
 	 * @covers BagOStuff::getScopedLock
 	 */
@@ -316,4 +379,11 @@ class BagOStuffTest extends MediaWikiTestCase {
 		$this->assertTrue( $this->cache->unlock( $key2 ) );
 		$this->assertTrue( $this->cache->unlock( $key2 ) );
 	}
+
+	public function tearDown() {
+		$this->cache->delete( $this->cache->makeKey( self::TEST_KEY ) );
+		$this->cache->delete( $this->cache->makeKey( self::TEST_KEY ) . ':lock' );
+
+		parent::tearDown();
+	}
 }

tests/phpunit/includes/objectcache/MemcachedBagOStuffTest.php

@@ -8,7 +8,7 @@ class MemcachedBagOStuffTest extends MediaWikiTestCase {
 
 	protected function setUp() {
 		parent::setUp();
-		$this->cache = new MemcachedBagOStuff( [ 'keyspace' => 'test' ] );
+		$this->cache = new MemcachedPhpBagOStuff( [ 'keyspace' => 'test', 'servers' => [] ] );
 	}
 
 	/**