[
https://issues.apache.org/jira/browse/BEAM-7495?focusedWorklogId=260683&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-260683
]
ASF GitHub Bot logged work on BEAM-7495:
----------------------------------------
Author: ASF GitHub Bot
Created on: 14/Jun/19 19:43
Start Date: 14/Jun/19 19:43
Worklog Time Spent: 10m
Work Description: aryann commented on pull request #8832: [BEAM-7495] Add
dynamic worker rebalancing to BigQuery Storage
URL: https://github.com/apache/beam/pull/8832#discussion_r293950722
##########
File path:
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryStorageStreamSource.java
##########
@@ -215,23 +223,101 @@ public T getCurrent() throws NoSuchElementException {
}
@Override
- protected long getCurrentOffset() throws NoSuchElementException {
- return currentOffset;
- }
-
- @Override
- public void close() {
+ public synchronized void close() {
storageClient.close();
}
@Override
public synchronized BigQueryStorageStreamSource<T> getCurrentSource() {
- return (BigQueryStorageStreamSource<T>) super.getCurrentSource();
+ return source;
}
@Override
- public boolean allowsDynamicSplitting() {
- return false;
+ public BoundedSource<T> splitAtFraction(double fraction) {
+ Metrics.counter(BigQueryStorageStreamReader.class,
"split-at-fraction-calls").inc();
+ LOGGER.info(
+ "Received split request for stream '{}' at fraction {}.",
+ source.stream.getName(),
+ fraction);
+
+ SplitReadStreamRequest splitRequest =
+ SplitReadStreamRequest.newBuilder()
+ .setOriginalStream(source.stream)
+ // TODO(aryann): Once we rebuild the generated client code, we
should change this to
+ // use setFraction().
+ .setUnknownFields(
+ UnknownFieldSet.newBuilder()
+ .addField(
+ 2,
+ UnknownFieldSet.Field.newBuilder()
+
.addFixed32(java.lang.Float.floatToIntBits((float) fraction))
+ .build())
+ .build())
+ .build();
+ SplitReadStreamResponse splitResponse =
storageClient.splitReadStream(splitRequest);
+
+ if (!splitResponse.hasPrimaryStream() ||
!splitResponse.hasRemainderStream()) {
+ // No more splits are possible!
+ Metrics.counter(
+ BigQueryStorageStreamReader.class,
+ "split-at-fraction-calls-failed-due-to-impossible-split-point")
+ .inc();
+ LOGGER.info("Stream '{}' cannot be split at {}.",
source.stream.getName(), fraction);
+ return null;
+ }
+
+ // We may be able to split this source. Before continuing, we pause the
reader thread and
+ // replace its current source with the primary stream iff the reader has
not moved past
+ // the split point.
+ synchronized (this) {
+ BigQueryServerStream<ReadRowsResponse> newResponseStream;
+ Iterator<ReadRowsResponse> newResponseIterator;
+ try {
+ newResponseStream =
+ storageClient.readRows(
+ ReadRowsRequest.newBuilder()
+ .setReadPosition(
+ StreamPosition.newBuilder()
+ .setStream(splitResponse.getPrimaryStream())
+ .setOffset(currentOffset + 1))
+ .build());
+ newResponseIterator = newResponseStream.iterator();
+ newResponseIterator.hasNext();
+ } catch (FailedPreconditionException e) {
+ // The current source has already moved past the split point, so
this split attempt
+ // is unsuccessful.
+ Metrics.counter(
+ BigQueryStorageStreamReader.class,
+ "split-at-fraction-calls-failed-due-to-bad-split-point")
+ .inc();
+ LOGGER.info(
+ "Split of stream '{}' abandoned because the primary stream is to
the left of "
+ + "the split fraction {}.",
+ source.stream.getName(),
+ fraction);
+ return null;
+ } catch (Exception e) {
+ Metrics.counter(
+ BigQueryStorageStreamReader.class,
+ "split-at-fraction-calls-failed-due-to-other-reasons")
+ .inc();
+ throw e;
+ }
+
+ // Cancels the parent stream before replacing it with the primary
stream.
+ responseStream.cancel();
+
+ currentOffset++;
+ source = source.fromExisting(splitResponse.getPrimaryStream());
Review comment:
The offset is not a property of the source or stream resource. It's a
property of the ReadRows request/streaming RPC. Above we create a new
client-server stream that begins with the right offset (responseStream) and we
replace the current one with it.
However, we also save a reference to the BigQueryStorageStreamSource
pointing to the primary stream, and a client can get access to that through
BigQueryStorageStreamReader#getCurrentSource. Does that source need to start at
whatever offset the parent reader was at when split happened OR does it have to
start at 0 (i.e., retaining the property of starting where the parent stream
initially started)?
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Issue Time Tracking
-------------------
Worklog Id: (was: 260683)
Time Spent: 1h 40m (was: 1.5h)
Remaining Estimate: 502h 20m (was: 502.5h)
> Add support for dynamic worker re-balancing when reading BigQuery data using
> Cloud Dataflow
> -------------------------------------------------------------------------------------------
>
> Key: BEAM-7495
> URL: https://issues.apache.org/jira/browse/BEAM-7495
> Project: Beam
> Issue Type: New Feature
> Components: io-java-gcp
> Reporter: Aryan Naraghi
> Assignee: Aryan Naraghi
> Priority: Major
> Original Estimate: 504h
> Time Spent: 1h 40m
> Remaining Estimate: 502h 20m
>
> Currently, the BigQuery connector for reading data using the BigQuery Storage
> API does not support any of the facilities on the source for Dataflow to
> split streams.
>
> On the server side, the BigQuery Storage API supports splitting streams at a
> fraction. By adding support to the connector, we enable Dataflow to split
> streams, which unlocks dynamic worker re-balancing.
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