Nicolae Vartolomei 425dc4b11b Add unique identifiers IMergeTreeDataPart structure ...

For now uuids are not generated at all, they are present only if the
part is updated manually (as you can see in the integration test).

The only place where they can be seen today by an end user is in
`system.parts` table. I was looking for hiding this column behind an
option but couldn't find an easy way to do that.

Likely this is also required for WAL, but need to think how not to break
compatibility.

Relates to #13574, https://github.com/ClickHouse/ClickHouse/issues/13574

Next 1: In the upcoming PR the plan is to integrate de-duplication based on
these fingerprints in the query pipeline.

Next 2: We'll enable automatic generation of uuids and come up with a
way for conditionally sending uuids when processing distributed queries
only when part movement is in progress.

2020-11-19 13:14:25 +00:00

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