> On Jun 5, 2019, at 2:07 PM, Riccardo Tasso <riccardo.ta...@gmail.com> wrote:
>
>
> Considering that the IndexUpgrader will efficiently do the most of the work
> I should investigate how to fill this gap, without reindexing from scratch.
>
>
This is actually a problem. IndexUpgraderTool creates a single massive segment,
essentially an optimize. Here are the reasons that’s bad:
https://lucidworks.com/2017/10/13/segment-merging-deleted-documents-optimize-may-bad/
IndexUpgraderTool does _not_ respect the max segment size even now, so the
linked article in the one above about how optimize may not be so bad in Solr
7.5+ is irrelevant.
Textual data is most sensitive to the changes in how Lucene works, other than
deprecated types. I strongly recommend you bite the bullet and re-index from
your system of record.
Best,
Erick
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