Index caching was disabled by default because it caused performance regressions
for some small-partition workloads. See https://github.com/scylladb/scylladb/issues/11202.
However, it also means that there are workloads which could benefit from the
index cache, but (by default) don't.
As a compromise, we can set a default limit on the memory usage of index cache,
which should be small enough to avoid catastrophic regressions in
small-partition workloads, but big enough to accommodate workloads where
index cache is obviously beneficial.
This series adds such a configurable limit, sets it to to 0.2 of total cache memory by default,
and re-enables index caching by default.
Fixes#15118Closes#14994
* github.com:scylladb/scylladb:
test: boost/cache_algorithm_test: add cache_algorithm_test
sstables: partition_index_cache: deglobalize stats
utils: cached_file: deglobalize cached_file metrics
db: config: enable index caching by default
config: add index_cache_fraction
utils: lru: add move semantics to list links
9a3d57256a