L1 (caffeine) cache hits/misses metrics not emitted

["Vararu, Vadim" <va...@adswizz.com>]

Hi all,

I’ve found out that the L1 cache hits/misses metrics are not emitted. Only the total number of requests (hits+misses). Any reason for that? Where could I suggest that to be implemented? It seems essential when it comes to caching and I see no technical challenge with that.

Thanks,
Vadim.

Re: L1 (caffeine) cache hits/misses metrics not emitted

[Gian Merlino <gi...@apache.org>]

Hey Vadim,

According to
https://druid.apache.org/docs/latest/operations/metrics.html#cache, today,
the number of hits and misses for the hybrid cache are both emitted, but
there isn't differentiation between L1 hits and L2 hits. Is that what you
mean?

If so, I think the main issue is there just isn't any place for them in the
metric schema described in the doc page above. There's just one set of
standardized "query/cache/delta/" and "query/cache/total/" metrics, without
specifying how things would be broken down if you had a multi-level cache.
If you proposed an update to the schema that maintains compatibility with
the existing one (this'll probably mean emitting some new metrics), I think
that'd be a good start. Then you could implement it and have it
incorporated into Druid via pull request.

On Wed, Feb 24, 2021 at 12:37 AM Vararu, Vadim <va...@adswizz.com>
wrote:

> Hi all,
>
> I’ve found out that the L1 cache hits/misses metrics are not emitted. Only
> the total number of requests (hits+misses). Any reason for that? Where
> could I suggest that to be implemented? It seems essential when it comes to
> caching and I see no technical challenge with that.
>
> Thanks,
> Vadim.
>