uschindler commented on PR #13535:
URL: https://github.com/apache/lucene/pull/13535#issuecomment-2204533884

   > I believe that this could be a problem for cross-data-structure merging 
concurrency (which we just disabled, but would like to re-enable soon-ish) 
since merging uses `READONCE`. In this case, I'd expect a `SegmentReader` to be 
opened in one thread, and then `XXXProducer#getMergeInstance()` (a `clone()` 
optimized for merging) to be called on the thread where the actual merging 
happens. So while the clone would be consumed in the thread where it's been 
created, the arena was previously initialized in a different thread?
   
   Merging uses sequential read ahead but from my review it never passes the 
constant IOContext.READONCE (see the link with references to READONCE above).
   
   Merging uses an IOContext with a MergeInfo attached. This uses same 
ReadAdvice SEQUENTIAL, but that different to READONCE. Or do I miss something?


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