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Major Description
Today we pass IOContext.DEFAULT. If DV updates are used in conjunction w/ NRTCachingDirectory, it means the latter will attempt to write the entire DV field in its RAMDirectory, which could lead to OOM.
Would be good if we can build our own FlushInfo, estimating the number of bytes we're about to write. I didn't see off hand a quick way to guesstimate that - I thought to use the current DV's sizeInBytes as an approximation, but I don't see a way to get it, not a direct way at least.
Maybe we can use the size of the in-memory updates to guesstimate that amount? Something like sizeOfInMemUpdates * (maxDoc/numUpdatedDocs)? Is it a too wild guess?