We have two mechanism to give visibility into reads having to process many tombstones:
* a warning in the logs, triggered if a read processed more the `tombstone_warn_threshold` dead rows/tombstones
* a trace message, which includes stats of the amount of rows in the page, including the amount of live and dead rows as well as tombstones
This series extends this to also include information on cells, so we have visibility into the case where a read has to process an excessive amount of cell tombstones (mainly because of collections).
A log line is now also logged if the amount of dead cells/tombstones in the page exceeds `tombstone_warn_threshold`. The trace message is also extended to contain cell stats.
The `tombstone_warn_threshold` log lines now receive a 10s rate-limit to avoid excessive log spamming. The rate-limit is separate for the row and cell logs.
Example of the new log line (`tombstone_warn_threshold=10` ):
```
WARN 2024-05-30 07:56:44,979 [shard 0:stmt] querier - Read 98 live cells and 126 dead cells/tombstones for system_schema.scylla_tables <partition-range-scan> (-inf, +inf) (see tombstone_warn_threshold)
```
Example of the new tracing message:
```
Page stats: 1 partition(s), 0 static row(s) (0 live, 0 dead), 1 clustering row(s) (1 live, 0 dead), 0 range tombstone(s) and 13 cell(s) (1 live, 12 dead) [shard 0] | 2024-05-30 08:13:19.690803 | 127.0.0.1 | 6114 | 127.0.0.1
```
Fixes: https://github.com/scylladb/scylladb/issues/18996
Improvement, not a backport candidate.
Closesscylladb/scylladb#18997
* github.com:scylladb/scylladb:
test/boost: mutation_test: add test for cell compaction stats
mutation/compact_and_expire_result: drop operator bool()
querier: consume_page(): add rate-limiting to tombstone warnings
querier: consume_page(): add cell stats to page stats trace message
querier: consume_page(): add tombstone warning for cell tombstones
querier: consume_page(): extract code which logs tombstone warning
mutation/mutation_compactor: collect and aggregate cell compaction stats
mutation: row::compact_and_expire(): use compact_and_expire_result
collection_mutation: compact_and_expire(): use compact_and_expire_result
mutation: introduce compact_and_expire_result
12c68bcf75