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The Apache Ignite can support cache rebalancing as transferring partition files using zero copy algorithm [1] based on an extension of communication SPI and Java NIO API. When the partition file has been transferred to the demander node there are two a few possible approaches can be implemented to preload entries from particular partition file.
The demander node will initialize a preloaded partition file as a new PageStore, make this storage up-to-date by applying previously saved async cache operations and then hot swap it under the checkpoint write lock.
Disadvantages:
Demander node first under checkpoint write lock must swap cache data storage with the temporary one to perform recovery operations under original cache data storage. After partition file has been received from the Supplier node there are to possible cases to make this partition file up-to-date.
Disadvantages:
The demander node will use a preloaded patition file as a new source of cache data entries to load.
Disadvantages:
In the process of balancing data:
The whole process is described in terms of rebalance single cache group and partition files would be rebalanced one-by-one:
After partition is received the historical rebalance must be initiated to load other cache updates.
The swapped temporary storage will log all the cache updates to the temporary WAL storage (per each partition) for further applying them to the corresponding partition file. While the Demander is being receive partition files it must save sequentially all cache entries corresponding to the MOVING partition into a new temporary storage. These entries will be applied later one by one on the newly received cache partition file. All asynchronous operations will be enrolled to the end of temporary storage during storage reads until it becomes fully read. The file-based FIFO approach assumes to be used by this process.
The temporary storage is chosen to be WAL-based. The storage must support to:
Expected problems to be solved
The demander node will use a preloaded patition file as a new source of cache data entries to load.
Disadvantages:
In the process of balancing data:
The whole process is described in terms of rebalancing a single partition file of a cache group. All the other partitions would be rebalanced one-by-one.
In terms of a high-level abstraction, Apache Ignite must support the features described below.
Partition preloader must support The node partition preloader machinery download cache partition file relocation files from one cluster node to another cluster nodes which owns desired partitions (the zero copy algorithm [1] assume to be used by default). To achieve this, the file transfer machinery transmission process must be implemented at Apache Ignite over Communication SPI.
Ignite's IThe Comminication SPI must support to:
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/** * */ public interface ChannelCommunicationListenerEx<T extends CloseableSerializable> extends EventListener { /** * @return@param ConnectionnodeId idRemote tonode remote nodeid. */ @param initMsg Init publicchannel ChannelId id(); message. /** @param channel * @return TheLocally created channel's configurationendpoint. */ public ChannelConfigvoid config(); /** * @return A map of all channel attributes. */ public Map<String, Serializable> attrs(); /** * @param name The name to get attribute. * @param <T> The attribute type. * @return The corresponding channel attribute instance. */ public <T extends Serializable> T attr(onChannelOpened(UUID nodeId, Message initMsg, Channel channel); } |
IO manager must support to:
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public interface TransmissionHandler { String name); /** * @param nameerr The err nameof tofail gethandling attributeprocess. * @param obj The chanel attribute instance. / * @param <T> The attribute type. */ public <T extends Serializable> void attronException(StringUUID namenodeId, TThrowable objerr); /** * @return@param <tt>true</tt>nodeId ifRemote thenode channelid isfrom configuredwhich andrequest readyhas tobeen usereceived. */ @param fileMeta File public boolean active(); meta info. /** * Make@return theAbsolute channelpathname readydenoting fora usefile. */ public voidString activate(filePath(UUID nodeId, TransmissionMeta fileMeta); } | ||||||||
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/** * */ public interface ChannelConfig { * <em>Chunk handler</em> represents /** by itself the way of *input Getsdata the channel's modestream processing. */ It accepts public boolean blocking(); /**within each chunk a {@link ByteBuffer} with data from input for further processing. * @param blocking The channel's mode* to@param set. nodeId Remote node id from *which @returnrequest Thehas configbeen instancereceived. */ @param initMeta Initial publichandler ChannelConfig blocking(boolean blocking); meta info. /** @return Instance of chunk handler *to Getsprocess theincoming timeoutdata optionby optionchunks. */ public intConsumer<ByteBuffer> timeout(chunkHandler(UUID nodeId, TransmissionMeta initMeta); /** * @param<em>File millishandler</em> Therepresents timeoutby initself milliseconds. the way of input data * @return The config instance.stream processing. All the data will */ be processed under publicthe ChannelConfighood timeout(int millis); } | ||||||||
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public interface CommunicationSpi<T extends Serializable> extends IgniteSpi { using zero-copy transferring algorithm and only start file processing and /** the end of processing *will @parambe remoteprovided. Destination cluster node to communicate with.* * @param attrsnodeId ConfigurationRemote channelnode attributes. id from which request has * @throws IgniteSpiException If failsbeen received. */ @param initMeta Initial publichandler defaultmeta Channel channel(ClusterNode remote, Map<String, Serializable> attrs) throws IgniteSpiException { throw new UnsupportedOperationException(); } }info. * @return Intance of read handler to process incoming data like the {@link FileChannel} manner. */ public Consumer<File> fileHandler(UUID nodeId, TransmissionMeta initMeta); } |
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public interfaceclass CommunicationListener<TTransmissionSender extends Serializable> extends EventListenerimplements Closeable { /** * @param chfile ASource channel instancefile to processsend configureto requestremote. * @param @returnparams Additional attributestransfer tofile send to remote node.description keys. */ @param plc The publicpolicy defaultof Map<String,handling Serializable>data onChannelConfigure(Channel ch) {on remote. * @throws IgniteCheckedException returnIf null;fails. }*/ public void /**send( * @param nodeId Remote node id.File file, * @param ch LocallyMap<String, created channel endpoint.Serializable> params, */ TransmissionPolicy publicplc default void) onChannelCreated(UUIDthrows nodeIdIgniteCheckedException, ChannelInterruptedException, ch)IOException { // No-op.send(file, 0, file.length(), params, plc); } } |
The file transmission manager must support to:
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/** * */ public interface FileWriter extends Closeable { /** * @param file The source file to send at. * @param offset The position to start /** * @param file Source file to send to remote. * @param plc The policy of handling data on remote. * @throws IgniteCheckedException If fails. */ public void send( File file, TransmissionPolicy plc ) throws IgniteCheckedException, InterruptedException, IOException { send(file, 0, file.length(), new HashMap<>(), plc); } /** * @param file Source file to send to remote. * @param offset Position to start trasfer at. * @param countcnt The numberNumber of bytes to transfer. * @param params The additionalAdditional transfer file description keys. * @param plc The policy of handling data on remote. * @throws IgniteCheckedException If fails. */ public void writesend( File file, long offset, long countcnt, Map<String, Serializable> params, ReadPolicyTransmissionPolicy plc ) throws IgniteCheckedException; } | ||||||||
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/** * */ public interface TransmitSession {, InterruptedException, IOException { // Impl. /** * @param nodeId The remote node id connected from. * @param sessionId The unique session id. */ public void begin(UUID nodeId, String sessionId); /** * @return The instance of read handler to process incoming data by chunks. */ public ChunkHandler chunkHandler(); /** * @return The intance of read handler to process incoming data like the {@link FileChannel} manner. */ public FileHandler fileHandler(); /** * The end of session transmission process. */ public void end(); /** * @param cause The cause of fail handling process. */ public void onException(Throwable cause); } |
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/**
*
*/
public interface FileHandler {
/**
* @param name The file name transfer from.
* @param position The start position pointer of download file in original source.
* @param count Total count of bytes readed from the original source.
* @param params The additional transfer file description params.
* @return The absolute pathname string denoting the file or {@code null} if there is no sense.
* @throws IOException If fails.
*/
public String begin(String name, long position, long count, Map<String, Serializable> params) throws IOException;
/**
* @param file The file with fully downloaded data into.
* @param params The additional transfer file description params.
*/
public void end(File file, Map<String, Serializable> params);
} |
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/**
*
*/
public interface ChunkHandler {
/**
* @param name The file name on remote.
* @param position The start position pointer of downloading file in original source.
* @param count Total count of bytes to read from the original source.
* @param params The additional transfer file description params.
* @return The size of of {@link ByteBuffer} to read the input channel into.
* @throws IOException If fails.
*/
public int begin(String name, long position, long count, Map<String, Serializable> params) throws IOException;
/**
* @param buff The data filled buffer.
* @return {@code true} if the chunk of data have been successfully accepted.
* @throws IOException If fails.
*/
public boolean chunk(ByteBuffer buff) throws IOException;
/**
* @param params The additional handling channel description params.
*/
public void end(Map<String, Serializable> params);
} |
When the supplier node receives the cache partition file demand request it will send the file over the CommunicationSpi. The cache partition file can be concurrently updated by checkpoint thread during its transmission. To guarantee the file consistency Сheckpointer must use Copy-on-Write [3] tehnique and save a copy of updated chunk into the temporary file.
While the demander node is in the partition file transmission state it must save sequentially all cache entries corresponding to the MOVING partition into a new temporary storage. These entries will be applied later one by one on the newly received cache partition file. All asynchronous operations will be enrolled to the end of temporary storage during storage reads until it becomes fully read. The file-based FIFO approach assumes to be used by this process.
The temporary storage is chosen to be WAL-based. The storage must support to:
Expected problems to be solved
The node is ready to become partition owner when partition data is rebalanced and cache indexes are ready. For the message-based cluster rebalancing approach indexes are rebuilding simultaneously with cache data loading. For the file-based rebalancing approach, the index rebuild procedure must be finished before the partition state is set to the OWNING state.
The following changes needs to be made:
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/**
* @return {@code True} if new type of direct connections supported.
*/
public default boolean channelConnectionSupported() {
return false;
}
/**
* @param remote Destination cluster node to communicate with.
* @param msg Configuration channel message.
* @throws IgniteSpiException If fails.
*/
public default IgniteSocketChannel channel(ClusterNode remote, T msg) throws IgniteSpiException {
throw new UnsupportedOperationException();
} |
}
}
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When the supplier node receives the cache partition file demand request it will send the file over the CommunicationSpi. The cache partition file can be concurrently updated by checkpoint thread during its transmission. To guarantee the file consistency Сheckpointer must use Copy-on-Write [3] tehnique and save a copy of updated chunk into the temporary file.
The node is ready to become partition owner when partition data is rebalanced and cache indexes are ready. For the message-based cluster rebalancing approach indexes are rebuilding simultaneously with cache data loading. For the file-based rebalancing approach, the index rebuild procedure must be finished before the partition state is set to the OWNING state.
Ignite doesn't provide any recovery guarantees for the partitions with the MOVING state. The cache partitions will be fully loaded when the next rebalance procedure occurs.
The node which is beeing rebalancing left the cluster. For such nodes WAL is always disabled (all partitions have MOVING state due to this node is new for the cluster and has no cache data).
Since WAL is disabled we can guarantee that all operations with loaded partition files are safe to be done (renaming partition files, applying async updates) due to a cache directory will be fully dropped on recoveryApache Ignite doesn't provide any recovery guarantees for the partitions with the MOVING state. The cache partitions will be fully loaded when the next rebalance procedure occurs.
Each topology change event JOIN/LEFT/FAILED may or may not change cache affinity assignments of currently rebalacning caches. If assignments is not changed and the node is still needs partitions being rebalanced we can continue the current rebalance process (see for details IGNITE-7165).
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To provide basic recovery guarantees we must to:
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Recovery from different stages:
The SSL must be disabled to take an advantage of Java NIO zero-copy file transmission using FileChannel#transferTo method. If we need to use SSL the file must be splitted on chunks the same way to send them over the socket channel with ByteBuffer. As the SSL engine generally needs a direct ByteBuffer to do encryption we can't avoid copying buffer payload from the kernel level to the application level.
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