Details
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Task
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Resolution: Won't Fix
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Major - P3
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Storage NYC 2018-07-02
Description
In v3.6, --repair sort of handles lack of UUIDs in some collections by placing the node in kUpgradingTo36 FCV mode.
In v4.0, however, UUIDs should always be present, so there is no mode we can put it in where it is acceptable for UUIDs not to be present. Therefore, we shall fix up the UUIDs on --repair if any are missing. SERVER-33151 makes startup require all collections to have UUIDs. We can easily generate UUIDs on startup for non-replicated collections without complication (this is done by SERVER-33246). However, replicated collections require a cross replica set repair solution; and sharded collection require a cross cluster repair solution. That is what this ticket is for.
The sharding catalog also persists UUIDs in the config.collections collection on config servers, and config.cache.collections collection on shards. These may have to be considered as well.