"This series expose statistics from the row_cache in the cache_service API.
After this series the following methods will be available:
get_row_hits
get_row_requests
get_row_hit_rate
get_row_size
get_row_entries"
If we don't yield, we can run out of memory while moving a memtable into
cache.
This reduces the chance that writing an sstable will fail because we could
not transfer the memtable into the cache.
This expose the cache tracker and the num entries in the row cache so it
can be used by the API.
And it adds a const getter for the region.
Both are const and are used for inspecting only.
Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
When LSA reclaimer cannot reclaim more space by compaction, it
will reclaim data by evicting from evictable regions.
Currently the only evictable region is the one owned by the row cache.
_lru_len may get stale when row_cache instance goes out of scope
purging all its partitions from cache. I'm assuming we're not really
interested in the number of partitions here, but rather a measure of
occupancy, so I applied a simple fix of using LSA region occupancy
instead.
The logger class constructor registers itself with the logger registry,
in order to enable dynamically setting log levels. However, since
thread_local variables may be (and are) initialized at the time of first
use, when the program starts up no loggers are registered.
Fix by making loggers global, not thread_local. This requires that the
registry use locking to prevent registration happening on different threads
from corrupting the registry.
Note that technically global variables can also be initialized at the
point of first use, and there is no portable way for classes to self-register.
However this is the best we can do.
row_cache class is meant to cache data for given table by wrapping
some underlying data source. It gives away a mutation_reader which
uses in-memory data if possible, or delegates to the underlying reader
and populates the cache on-the-fly.
Accesses to data in cache is tracked for eviction purposes by a
separate entity, the cache_tracker. There is one such tracker for the
whole shard.
