scwhittle commented on code in PR #36112:
URL: https://github.com/apache/beam/pull/36112#discussion_r2340513364
##########
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Redistribute.java:
##########
@@ -190,21 +202,31 @@ public void processElement(
}
static class AssignShardFn<T> extends DoFn<T, KV<Integer, T>> {
- private int shard;
+ private int randomShard;
private @Nullable Integer numBuckets;
+ private boolean deterministicSharding;
- public AssignShardFn(@Nullable Integer numBuckets) {
+ public AssignShardFn(@Nullable Integer numBuckets, boolean
deterministicSharding) {
this.numBuckets = numBuckets;
+ this.deterministicSharding = deterministicSharding;
+ this.randomShard = 0;
}
@Setup
public void setup() {
- shard = ThreadLocalRandom.current().nextInt();
+ if (deterministicSharding) {
+ randomShard = ThreadLocalRandom.current().nextInt();
+ }
}
@ProcessElement
public void processElement(@Element T element, OutputReceiver<KV<Integer,
T>> r) {
- ++shard;
+ int shard = 0;
+ if (deterministicSharding && element != null) {
+ shard = element.hashCode();
Review Comment:
hashCode isn't deterministic across JVM restarts which we want this to be.
You can use FarmHash
https://guava.dev/releases/21.0/api/docs/com/google/common/hash/Hashing.html#farmHashFingerprint64--
To deterministically hash the right things you could have this dofn process
method take in ProcessContext and look at the offset or uniqueid from it. Since
that has some performance overhead I believe, you could have different dofn
impl for the random key assignment and the deterministic.
##########
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Redistribute.java:
##########
@@ -190,21 +202,31 @@ public void processElement(
}
static class AssignShardFn<T> extends DoFn<T, KV<Integer, T>> {
- private int shard;
+ private int randomShard;
private @Nullable Integer numBuckets;
+ private boolean deterministicSharding;
- public AssignShardFn(@Nullable Integer numBuckets) {
+ public AssignShardFn(@Nullable Integer numBuckets, boolean
deterministicSharding) {
this.numBuckets = numBuckets;
+ this.deterministicSharding = deterministicSharding;
+ this.randomShard = 0;
}
@Setup
public void setup() {
- shard = ThreadLocalRandom.current().nextInt();
+ if (deterministicSharding) {
Review Comment:
!deterministic?
##########
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Redistribute.java:
##########
@@ -158,7 +168,9 @@ public boolean getAllowDuplicates() {
@Override
public PCollection<T> expand(PCollection<T> input) {
return input
- .apply("Pair with random key", ParDo.of(new
AssignShardFn<>(numBuckets)))
Review Comment:
I think that changing the name means that update compatability woudl require
setting the transformnamemapping. Instead we could keep the name for the
previous behavior.
if (this.determinsticSharding) {
c = input.apply("Pair with deterministic key", ParDo.of())
} else {
c = input.apply("Pair with random key", ...)
}
return c.apply(Redistribute...)
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