robertwb commented on a change in pull request #13924:
URL: https://github.com/apache/beam/pull/13924#discussion_r578065831
##########
File path:
sdks/java/harness/src/main/java/org/apache/beam/fn/harness/data/PCollectionConsumerRegistry.java
##########
@@ -305,4 +336,59 @@ public double getProgress() {
return delegate.getProgress();
}
}
+
+ private static class SampleByteSizeDistribution<T> {
+ /** Basic implementation of {@link ElementByteSizeObserver} for use in
size estimation. */
+ private static class ByteSizeObserver extends ElementByteSizeObserver {
+ private long observedSize = 0;
+
+ @Override
+ protected void reportElementSize(long elementSize) {
+ observedSize += elementSize;
+ }
+ }
+
+ final Distribution distribution;
+
+ public SampleByteSizeDistribution(Distribution distribution) {
+ this.distribution = distribution;
+ }
+
+ public void tryUpdate(T value, Coder<T> coder) throws Exception {
+ if (shouldSampleElement() ||
coder.isRegisterByteSizeObserverCheap(value)) {
Review comment:
I think "cheap" is still relative, we should probably not sample every
element even in that case (e.g. it could be a bunch of nested tuples).
##########
File path:
sdks/java/harness/src/main/java/org/apache/beam/fn/harness/data/PCollectionConsumerRegistry.java
##########
@@ -305,4 +336,59 @@ public double getProgress() {
return delegate.getProgress();
}
}
+
+ private static class SampleByteSizeDistribution<T> {
+ /** Basic implementation of {@link ElementByteSizeObserver} for use in
size estimation. */
+ private static class ByteSizeObserver extends ElementByteSizeObserver {
+ private long observedSize = 0;
+
+ @Override
+ protected void reportElementSize(long elementSize) {
+ observedSize += elementSize;
+ }
+ }
+
+ final Distribution distribution;
+
+ public SampleByteSizeDistribution(Distribution distribution) {
+ this.distribution = distribution;
+ }
+
+ public void tryUpdate(T value, Coder<T> coder) throws Exception {
+ if (shouldSampleElement() ||
coder.isRegisterByteSizeObserverCheap(value)) {
+ // First try using byte size observer
+ ByteSizeObserver observer = new ByteSizeObserver();
+ coder.registerByteSizeObserver(value, observer);
+
+ if (!observer.getIsLazy()) {
+ observer.advance();
+ this.distribution.update(observer.observedSize);
+ } else {
+ // Coder byte size observation is lazy (requires iteration for
observation) so fall back
+ // to counting output stream
+ CountingOutputStream os = new
CountingOutputStream(ByteStreams.nullOutputStream());
+ coder.encode(value, os);
+ this.distribution.update(os.getCount());
+ }
+ }
+ }
+
+ // Lowest sampling probability: 0.001%.
+ private static final int SAMPLING_TOKEN_UPPER_BOUND = 1000000;
+ private static final int SAMPLING_CUTOFF = 10;
+ private int samplingToken = 0;
+ private Random randomGenerator = new Random();
+
+ private boolean shouldSampleElement() {
+ // Sampling probability decreases as the element count is increasing.
+ // We unconditionally sample the first samplingCutoff elements. For the
+ // next samplingCutoff elements, the sampling probability drops from 100%
+ // to 50%. The probability of sampling the Nth element is:
+ // min(1, samplingCutoff / N), with an additional lower bound of
+ // samplingCutoff / samplingTokenUpperBound. This algorithm may be
refined
+ // later.
+ samplingToken = Math.min(samplingToken + 1, SAMPLING_TOKEN_UPPER_BOUND);
+ return randomGenerator.nextInt(samplingToken) < SAMPLING_CUTOFF;
Review comment:
Maybe drop a TODO to implement
https://en.wikipedia.org/wiki/Reservoir_sampling#Fast_Approximation rather than
calling nextInt every time which could be expensive.
##########
File path:
sdks/java/harness/src/main/java/org/apache/beam/fn/harness/data/PCollectionConsumerRegistry.java
##########
@@ -305,4 +336,59 @@ public double getProgress() {
return delegate.getProgress();
}
}
+
+ private static class SampleByteSizeDistribution<T> {
+ /** Basic implementation of {@link ElementByteSizeObserver} for use in
size estimation. */
+ private static class ByteSizeObserver extends ElementByteSizeObserver {
+ private long observedSize = 0;
+
+ @Override
+ protected void reportElementSize(long elementSize) {
+ observedSize += elementSize;
+ }
+ }
+
+ final Distribution distribution;
+
+ public SampleByteSizeDistribution(Distribution distribution) {
+ this.distribution = distribution;
+ }
+
+ public void tryUpdate(T value, Coder<T> coder) throws Exception {
+ if (shouldSampleElement() ||
coder.isRegisterByteSizeObserverCheap(value)) {
+ // First try using byte size observer
+ ByteSizeObserver observer = new ByteSizeObserver();
+ coder.registerByteSizeObserver(value, observer);
+
+ if (!observer.getIsLazy()) {
+ observer.advance();
+ this.distribution.update(observer.observedSize);
+ } else {
+ // Coder byte size observation is lazy (requires iteration for
observation) so fall back
Review comment:
So this means we'll iterate over the element twice, once here, once when
it's consumed, right? We should probably at least drop a TODO to avoid this.
(This iteration will also update the observer, so will be more expensive.)
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