/**
* Gets a stream to read the data of a block. The stream is backed by Alluxio storage.
*
* @param blockId the block to read from
* @return a {@link BlockInStream} which can be used to read the data in a streaming fashion
* @throws IOException if the block does not exist
*/
public BufferedBlockInStream getInStream(long blockId) throws IOException {
BlockInfo blockInfo;
try (CloseableResource<BlockMasterClient> masterClientResource =
mContext.acquireMasterClientResource()) {
blockInfo = masterClientResource.get().getBlockInfo(blockId);
} catch (AlluxioException e) {
throw new IOException(e);
}
if (blockInfo.getLocations().isEmpty()) {
throw new IOException("Block " + blockId + " is not available in Alluxio");
}
// TODO(calvin): Get location via a policy.
// Although blockInfo.locations are sorted by tier, we prefer reading from the local worker.
// But when there is no local worker or there are no local blocks, we prefer the first
// location in blockInfo.locations that is nearest to memory tier.
// Assuming if there is no local worker, there are no local blocks in blockInfo.locations.
// TODO(cc): Check mContext.hasLocalWorker before finding for a local block when the TODO
// for hasLocalWorker is fixed.
String localHostName = NetworkAddressUtils.getLocalHostName(ClientContext.getConf());
for (BlockLocation location : blockInfo.getLocations()) {
WorkerNetAddress workerNetAddress = location.getWorkerAddress();
if (workerNetAddress.getHost().equals(localHostName)) {
// There is a local worker and the block is local.
try {
return new LocalBlockInStream(blockId, blockInfo.getLength());
} catch (IOException e) {
LOG.warn("Failed to open local stream for block " + blockId + ". " + e.getMessage());
// Getting a local stream failed, do not try again
break;
}
}
}
// No local worker/block, get the first location since it's nearest to memory tier.
WorkerNetAddress workerNetAddress = blockInfo.getLocations().get(0).getWorkerAddress();
return new RemoteBlockInStream(blockId, blockInfo.getLength(), workerNetAddress);
}
/**
* Attempts to promote a block in Alluxio space. If the block is not present, this method will
* return without an error. If the block is present in multiple workers, only one worker will
* receive the promotion request.
*
* @param blockId the id of the block to promote
* @throws IOException if the block does not exist
*/
public void promote(long blockId) throws IOException {
BlockInfo info;
try (CloseableResource<BlockMasterClient> blockMasterClientResource =
mContext.acquireMasterClientResource()) {
info = blockMasterClientResource.get().getBlockInfo(blockId);
} catch (AlluxioException e) {
throw new IOException(e);
}
if (info.getLocations().isEmpty()) {
// Nothing to promote
return;
}
// Get the first worker address for now, as this will likely be the location being read from
// TODO(calvin): Get this location via a policy (possibly location is a parameter to promote)
WorkerNetAddress workerAddr = info.getLocations().get(0).getWorkerAddress();
BlockWorkerClient blockWorkerClient = mContext.acquireWorkerClient(workerAddr.getHost());
try {
blockWorkerClient.promoteBlock(blockId);
} catch (AlluxioException e) {
throw new IOException(e);
} finally {
mContext.releaseWorkerClient(blockWorkerClient);
}
}