Did the strength of the event-timestamp-incrementation increase in very recent memory?
I believe this particular message (max_rawsize_perchunk) has to do with the SIZE of the events.
The _raw is the text of the events, so rawsize perchunk has to do with when we read a chunk (this can be different quantities of events based on a few factors like batch mode vs nonbatch, size of buckets, distribution across time, etc), but typically is capped at ten thousand (10,000). To avoid bad scenarios like reading in 10,000 events each of which are 1MB of text in size (oops, 10GB of raw and your box falls over), there's a ceiling on the maximum amount of data we're willing to read in from _raw.
If this feature is working ideally, you could still get a slowdown if that chunk pushed your system into a low memory scenario which might cause some amount of swapping until the search exits. If the feature is not working well, then it could cause slowdowns for other reasons (that I don't know).
I would suggest checking the memory scenario on the index nodes and the search head, and if no one else has a better answer about this problem working with support to nail it down.
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