Hi Sebastien,
What's your goal? Improving cache hit rate purely for the sake of having
a higher hit rate is rarely a good goal, because higher cache hit rate
doesn't always mean faster operations.
Do you have specific issues with performance? If so, can you please tell
us more about it? This way, we can focus on that.
Cheers,
Bowen
On 27/11/2023 14:59, Sébastien Rebecchi wrote:
Hello
When I use nodetool info, it prints that relevant information
Heap Memory (MB) : 14229.31 / 32688.00
Off Heap Memory (MB) : 5390.57
Key Cache : entries 670423, size 100 MiB, capacity 100
MiB, 13152259 hits, 47205855 requests, 0.279 recent hit rate, 14400
save period in seconds
Chunk Cache : entries 63488, size 992 MiB, capacity 992
MiB, 143250511 misses, 162302465 requests, 0.117 recent hit rate,
2497.557 microseconds miss latency
Here I focus on lines relevant for that conversation. And the numbers
are roughly the same for all nodes of the cluster.
The key and chunk caches are full and the hit rate is low. At the same
time the heap memory is far from being used at full capacity.
I would say that I can significantly increase the sizes of those
caches in order to increase hit rate and improve performance.
In cassandra.yaml, key_cache_size_in_mb has a blank value, so 100 MiB
by default, and file_cache_size_in_mb is set to 1024.
I'm thinking about setting key_cache_size_in_mb to 1024
and file_cache_size_in_mb to 2048. What would you recommend? Is anyone
having good experience with tuning those parameters?
Thank you in advance.
Sébastien.
