Introduces support to split large partitions during compaction. Today, compaction can only split input data at partition boundary, so a large partition is stored in a single file. But that can cause many problems, like memory pressure (e.g.: https://github.com/scylladb/scylladb/issues/4217), and incremental compaction can also not fulfill its promise as the file storing the large partition can only be released once exhausted.
The first step was to add clustering range metadata for first and last partition keys (retrieved from promoted index), which is crucial to determine disjointness at clustering level, and also the order at which the disjoint files should be opened for incremental reading.
The second step was to extend sstable_run to look at clustering dimension, so a set of files storing disjoint ranges for the same partition can live in the same sstable run.
The final step was to introduce the option for compaction to split large partition being written if it has exceeded the size threshold.
What's next? Following this series, a reader will be implemented for sstable_run that will incrementally open the readers. It can be safely built on the assumption of the disjoint invariant after the second step aforementioned.
Closes#11233
* github.com:scylladb/scylladb:
test: Add test for large partition splitting on compaction
compaction: Add support to split large partitions
sstable: Extend sstable_run to allow disjointness on the clustering level
sstables: simplify will_introduce_overlapping()
test: move sstable_run_disjoint_invariant_test into sstable_datafile_test
test: lib: Fix inefficient merging of mutations in make_sstable_containing()
sstables: Keep track of first partition's first pos and last partition's last pos
sstables: Rename min/max position_range to a descriptive name
sstables_manager: Add sstable metadata reader concurrency semaphore
sstables: Add ability to find first or last position in a partition
05ef13a627