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https://issues.apache.org/jira/browse/LUCENE-5591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13984234#comment-13984234
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Shai Erera commented on LUCENE-5591:
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BTW, I started by adding {{ramBytesUsed()}} to {{DocValuesFieldUpdates}}, but
that was way over estimated, especially when the number of updates is small.
That's due to the buffers used by these classes, e.g. GrowableWriter with
pageSize=1024. I don't think that the RAM representation should be used as an
estimate, rather the avg-update size is closer to what will eventually be
written to disk.
> ReaderAndUpdates should create a proper IOContext when writing DV updates
> -------------------------------------------------------------------------
>
> Key: LUCENE-5591
> URL: https://issues.apache.org/jira/browse/LUCENE-5591
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Shai Erera
> Attachments: LUCENE-5591.patch
>
>
> 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?
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