Segments Info
The Segments Info screen lets you see a visualization of the various segments in the underlying Lucene index for this core, with information about the size of each segment – both bytes and in number of documents – as well as other basic metadata about those segments. Most visible is the number of deleted documents, but you can hover your mouse over the segments to see additional numeric details.
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This information may be useful for people to help make decisions about the optimal merge settings for their data.