Simon Willnauer 2c3bd32aff Add a merge policy that prunes ID postings for soft-deleted but retained documents (#40741)
This change adds a merge policy that drops all _id postings for documents that
are marked as soft-deleted but retained across merges. This is usually unnecessary
unless soft-deletes are used with a retention policy since otherwise a merge would
remove deleted documents anyway.

Yet, this merge policy prevents extreme cases where a very large number of soft-deleted
documents are retained and are impacting update performance.
Note, using this merge policy will remove all lookup by ID capabilities for soft-deleted documents.
2019-06-06 13:41:46 +02:00
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