Recently we observed an OOM caused by the partition based splitting
writer going crazy, creating 1.7K buckets while scrubbing an especially
broken sstable. To avoid situations like that in the future, this patch
provides a max limit for the number of live buckets. When the number of
buckets reach this number, the largest bucket is closed and replaced by
a bucket. This will end up creating more output sstables during scrub
overall, but now they won't all be written at the same time causing
insane memory pressure and possibly OOM.
Scrub compaction sets this limit to 100, the same limit the TWCS's
timestamp based splitting writer uses (implemented through the
classifier -
time_window_compaction_strategy::max_data_segregation_window_count).
Fixes: #9400
Tests: unit(dev)
Closes#9401
970fe9a339