Tuning the Scylla data cache

[Pau Freixes]

Hi,

I've been reading this blog post [1] about how works, it says that

> Rows are freed starting from the least recently used ones, with insertion counting as a use ..

Is there any way of tuning this? so counting only the reads.

Correct me if I'm wrong but, for workloads where you have a continuous
flow of writes for different keys but only a small subset of them are
often used at reading time and are also not frequently updated, the
fact of counting any individual write would reduce the hit ratio
level, making this feature useless in some scenarios.


[1] https://www.scylladb.com/2018/07/26/how-scylla-data-cache-works/

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--pau

[Tomasz Grabiec]

On Wed, Sep 18, 2019 at 3:27 PM Pau Freixes <pfre...@gmail.com> wrote:

Hi,

I've been reading this blog post [1] about how  works, it says that

> Rows are freed starting from the least recently used ones, with insertion counting as a use ..

Is there any way of tuning this? so counting only the reads.

There is no way to tune this currently, other than disabling caching.

 

Correct me if I'm wrong but, for workloads where you have a continuous
flow of writes for different keys but only a small subset of them are
often used at reading time and are also not frequently updated, the
fact of counting any individual write would reduce the hit ratio
level, making this feature useless in some scenarios.

Yes, we have plans to address this. It's tracked here: https://github.com/scylladb/scylla/issues/3643

Also related:

https://github.com/scylladb/scylla/issues/1504

https://github.com/scylladb/scylla/issues/194

https://github.com/scylladb/scylla/issues/3429

 

[erozycki@edoinc.com]

How can I disable the cache? I think it may be beneficial for my workload. https://docs.scylladb.com/faq/#do-i-ever-need-to-disable-the-scylla-cache-to-use-less-memory says that it's not possible. Or are you referring to BYPASS CACHE in the upcoming 3.1 release?

[Avi Kivity]

There is an enable_cache option in scylla.yaml.

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