FrankChen021 commented on code in PR #20090:
URL: https://github.com/apache/druid/pull/20090#discussion_r3821777715
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extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchBufferAggregatorHelper.java:
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@@ -38,8 +36,8 @@ final class SketchBufferAggregatorHelper
{
private final int size;
private final int maxIntermediateSize;
- private final IdentityHashMap<ByteBuffer, Int2ObjectMap<Union>> unions = new
IdentityHashMap<>();
- private final IdentityHashMap<ByteBuffer, WritableMemory> memCache = new
IdentityHashMap<>();
+ private final ConcurrentHashMap<ByteBuffer, ConcurrentHashMap<Integer,
Union>> unions = new ConcurrentHashMap<>();
Review Comment:
[P1] Do not key caches by mutable ByteBuffers
ConcurrentHashMap uses ByteBuffer.equals/hashCode, which depend on the
buffer's remaining contents. Union updates mutate those contents in place,
changing the key hash after insertion. Subsequent unions.get(buf) calls can
miss and get() returns SketchHolder.EMPTY; distinct equal-content buffers can
also alias. Preserve identity/stable-key semantics while making access
concurrent.
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