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Relax memory barrier from org.elasticsearch.action.search.AbstractSearchAsyncAction#hasShardResponse #124888

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Relax memory barrier from org.elasticsearch.action.search.AbstractSearchAsyncAction#hasShardResponse #124888

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4 changes: 2 additions & 2 deletions server/src/main/java/org/elasticsearch/action/search/AbstractSearchAsyncAction.java
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Original file line number Diff line number Diff line change
Expand Up @@ -494,7 +494,7 @@ private static boolean isTaskCancelledException(Exception e) {
protected void onShardResult(Result result) {
assert result.getShardIndex() != -1 : "shard index is not set";
assert result.getSearchShardTarget() != null : "search shard target must not be null";
hasShardResponse.set(true);
hasShardResponse.compareAndExchangeRelease(false, true);
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@andreidan andreidan Mar 17, 2025

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Can you please document why acquire semantics are not needed here?

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@original-brownbear original-brownbear Mar 17, 2025

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Hmm same question here, does it really make sense to document this? We have no data dependency between this field and any other field and we only go false -> true here so if we do a plain read that's good enough, a potentially redundant write is still an improvement of the previous version. Maybe we should come up with a general list of what to use for what instead?

if (logger.isTraceEnabled()) {
logger.trace("got first-phase result from {}", result != null ? result.getSearchShardTarget() : null);
}
Expand Down Expand Up @@ -734,7 +734,7 @@ protected final ShardSearchRequest buildShardSearchRequest(SearchShardIterator s
// can return a null response if the request rewrites to match none rather
// than creating an empty response in the search thread pool.
// Note that, we have to disable this shortcut for queries that create a context (scroll and search context).
shardRequest.canReturnNullResponseIfMatchNoDocs(hasShardResponse.get() && shardRequest.scroll() == null);
shardRequest.canReturnNullResponseIfMatchNoDocs(shardRequest.scroll() == null && hasShardResponse.getAcquire());
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@andreidan andreidan Mar 17, 2025

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Is the order swap of the acquire call and the shardRequest.scroll() call on purpose? If so, can you document why ?

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@original-brownbear original-brownbear Mar 17, 2025

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Hmm not sure it makes sense to add a comment for this, obviously a potentially shared read is more expensive than a plain read so I figured I'd just switch these two around? :No magic here )

return shardRequest;
}

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