elasticsearch/docs/reference/migration/migrate_6_0/cat.asciidoc

[[breaking_60_cat_changes]]
=== Cat API changes

==== Unbounded queue size in cat thread pool

Previously if a queue size backing a thread pool was unbounded, the cat thread pool API would output an empty string in
the queue_size column. This has been changed to now output -1 so that the output is always present and always numeric.