Add .set_skip_when_empty() to four metrics in the db module that are
only incremented on very rare error paths and are almost always zero:
- cache::pinned_dirty_memory_overload: described as 'should sit
constantly at 0, nonzero is indicative of a bug'
- corrupt_data::entries_reported: only fires on actual data corruption
- hints::corrupted_files: only fires on on-disk hint file corruption
- rate_limiter::failed_allocations: only fires when the rate limiter
hash table is completely full and gives up allocating, requiring
extreme cardinality pressure
These metrics create unnecessary reporting overhead when they are
perpetually zero. set_skip_when_empty() suppresses them from metrics
output until they become non-zero.
AI-Assisted: yes
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
Closesscylladb/scylladb#29344
Similar to large_data_handler, this interface allows sstable writers to
delegate the handling of corrupt data.
Two implementations are provided:
* system_table_corrupt_data_handler - saved corrupt data in
system.corrupt_data, with a TTL=10days (non-configurable for now)
* nop_corrupt_data_handler - drops corrupt data
