Here are three endpoints in the api/cache_service that report "metrics"
for the row cache and the values they return
- entries: number of partitions
- size: number of partitions
- capacity: used space
The size and capacity seem very inaccurate.
Comment says, that in C* the size should be weighted, but scylla doesn't
support weight of entries in cache. Also, capacity is configurable via
row_cache_size_in_mb config option or set_row_cache_capacity_in_mb API
call, but Scylla doesn't support both either.
This patch suggestes changing return values for size and capacity endpoints.
Despite row cache doesn't support weights, it's natural to return
used_space in bytes as the value, which is more accurate to what "size"
means rather than number of entries.
The capacity may return back total memory size, because this is what
Scylla really does -- row cache growth is only limited by other memory
consumers, not by configured limits.
fixes: #9418
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#17724
def5fed619