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From Todd Lipcon <t...@cloudera.com>
Subject Re: How to flush `block_cache_capacity_mb` easily?
Date Fri, 07 Apr 2017 20:05:53 GMT
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.


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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