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From Jason Heo <jason.heo....@gmail.com>
Subject Re: How to flush `block_cache_capacity_mb` easily?
Date Mon, 10 Apr 2017 01:38:32 GMT
Hi Todd.

I hope you had a good weekend.

Exactly, I'm testing the latency of cold-cache reads from SATA disks and
performance of difference schema designs as well.

We currently using Elasticsearch for a analytic service. ES has a "clear
cache API" feature, it makes me easy to test.



2017-04-08 5:05 GMT+09:00 Todd Lipcon <todd@cloudera.com>:

> Hey Jason,
> Can I ask what the purposes of the testing is?
> One thing to note is that we're currently leaving a fair bit of
> performance on the table for cold-cache reads from spinning disks. So, if
> you find that the performance is not satisfactory, it's worth being aware
> that we will likely make some significant improvements in this area in the
> future.
> https://issues.apache.org/jira/browse/KUDU-1289 has some details.
> -Todd
> On Fri, Apr 7, 2017 at 8:44 AM, Dan Burkert <danburkert@apache.org> wrote:
>> Hi Jason,
>> There is no command to have Kudu evict its block cache, but restarting
>> the tablet server process will have that effect.  Ideally all written data
>> will be flushed before the restart, otherwise startup/bootstrap will take a
>> bit longer. Flushing typically happens within 60s of the last write.
>> Waiting for flush and compaction is also a best-practice for read-only
>> benchmarks.  I'm not sure if someone else on the list has an easier way of
>> determining when a flush happens, but I typically look at the 'MemRowSet'
>> memory usage for the tablet on the /mem-trackers HTTP endpoint; it should
>> show something minimal like 256B if it's fully flushed and empty.  You can
>> also see details about how much memory is in the block cache on that page,
>> if that interests you.
>> - Dan
>> On Thu, Apr 6, 2017 at 11:23 PM, Jason Heo <jason.heo.sde@gmail.com>
>> wrote:
>>> Hi.
>>> I'm using Apache Kudu 1.2 on CDH 5.10.
>>> Currently, I'm doing a performance test of Kudu.
>>> Flushing OS Page Cache is easy, but I don't know how to flush
>>> `block_cache_capacity_mb` easily.
>>> I currently execute SELECT statement over a unnecessarily table to evict
>>> cached block of testing table.
>>> It is cumbersome, so I'd like to know is there a command for flushing
>>> block caches (or another kudu's caches which I don't know yet)
>>> Thanks.
>>> Regards,
>>> Jason
> --
> Todd Lipcon
> Software Engineer, Cloudera

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