repair: Postpone data segregation to off-strategy compaction
repair: Postpone data segregation to off-strategy compaction

With data segregation on repair, thousands of sstables are potentially
added to maintenance set which causes high latency due to stalls.

That's because N*M sstables are created by a repair,
	where N = # of ranges
	and M = # of segregations

For TWCS, M = # of windows.

Assuming N = 768 and M = 20, ~15k sstables end up in sstable set

To fix this problem, let's avoid performing data segregation in repair,
as offstrategy will already perform the segregation anyway.

So from now on, only N non-overlapping sstables will be added to set.
Read amplification isn't affected because a query will only touch one
sstable in maintenance set.
When offstrategy starts, it will pick all sstables from set and
compact them in a single step while performing data segregation,
so data is properly laid out before integrated into the main set.

tests:
	- sstable_compaction_test.twcs_reshape_with_disjoint_set_test
	- mode(dev)
	- manual test using repair-based bootstrap

Fixes #9199.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <20210824185043.76475-1-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

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