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From Matthew Jacobs>
Subject Re: Impala user resource isolation best practice
Date Mon, 25 Jul 2016 16:23:35 GMT

If you set the query mem_limit the estimates are not used in this way,
and they're enforced at runtime. We recommend that you always set the
query mem_limits. In Impala 2.5 you can configure the admission
control pools to have a default query option mem_limit, e.g. every
query in poolA gets a default query mem_limit=5G, and perhaps poolB
gets a default query mem_limit=10g. You can still override those query
options if you'd like with "set mem_limit=X;". There is also an
impalad command line argument to set the default query options
(fallback in all cases): --default_query_options=‘mem_limit=X’


On Sun, Jul 24, 2016 at 8:25 PM, 廖松博 <> wrote:
> Hi Matt,
>         Thanks for suggestion. Even though we can solve "soft limit" problem using single
coordinator, the coordinator doesn't know how much memory will be used during execution. The
limit is actually based on the memory size estimated by coordinator, right. So it is possible
that the coordinator accept a query which using estimating 5G memory which under limit and
dispatch to workers, but the query actually use 15G memory during execution so limit doesn’t
make sense.
>         And as I know the estimation will be more accurate if the table has stats, right
? But it does not promise to be accurate even if stats exists.
>         Does the wrongly estimation matters ? For example will it cause the out of memory
problem ? If yes, is there any best practice to avoid that ?
>         Thank you very much.
> Songbo
> -----邮件原件-----
> 发件人: Matthew Jacobs []
> 发送时间: 2016年7月19日 11:35
> 收件人: 廖松博
> 抄送:
> 主题: Re: Impala user resource isolation best practice
> Hi Songbo,
> Yes, setting the MEM_LIMITs is a good idea. In Impala 2.5 and after, you can set a per-pool
default query mem limit. Cloudera Manager makes this easy in the Dynamic Resource Pools page.
> You are right about the possibility of overwhelming a single coordinator. You can consider
setting up one larger node to be a coordinator (e.g. a lot of RAM & CPUs), and setting
it so that it *does not* have a datanode on it to minimize the number of query fragments scheduled
on it. In order to do that you'll also need to set the impalad cmd line argument "-abort_on_config_error=false"
because it normally expects a DN to be colocated with the Impalad. It is still possible to
overwhelm a single coordinator like this, but we've found it to work reasonably well in our
tests. Of course it is very dependent on your hardware and workload.
> Best,
> Matt
> On Mon, Jul 18, 2016 at 6:31 PM, 廖松博 <> wrote:
>> Hi Matt,
>>         If we use a single coordinator, if a lot of queries come in, the coordinator
may be out of memory, right ? Because the coordinator take charge of merge results from workers
and send back to client.
>>         Thanks.
>> Songbo
>> -----邮件原件-----
>> 发件人: Matthew Jacobs []
>> 发送时间: 2016年7月19日 7:50
>> 收件人: 廖松博
>> 抄送:
>> 主题: Re: Impala user resource isolation best practice
>> The 'soft limits' refer to the behavior that, when multiple coordinators are used
and queries are submitted concurrently, the admission control cannot guarantee the limits
because the decisions are made based on some stale information that needs to be updated by
the statestore. If you use a single coordinator you avoid that problem. That said, a separate
problem is that there is no way to guarantee that other resources, e.g. network, IO, etc.
are not abused by a single user.
>> On Mon, Jul 18, 2016 at 4:29 PM, 廖松博 <> wrote:
>>> Hi Matthew,
>>>         Thanks for your reply. The point is , per admission control documents,
most of impala limits are "soft limit", are the 2 settings you mentioned also "soft limit"
? The soft limit means the pool will exceed the memory/concurrency limit at some moment when
impala is not aware of. But it is affecting other pool at that moment.
>>>         Thanks.
>>> Songbo
>>> -----邮件原件-----
>>> 发件人: Matthew Jacobs []
>>> 发送时间: 2016年7月19日 0:44
>>> 收件人:
>>> 主题: Re: Impala user resource isolation best practice
>>> By the way, some of the controls I mentioned were added in Impala 2.5, so you
should consider upgrading if you're not already using a newer version of Impala.
>>> Thanks,
>>> Matt
>>> On Mon, Jul 18, 2016 at 9:20 AM, Matthew Jacobs <> wrote:
>>>> Hi Songbo,
>>>> Right now the best you can do is with admission control with:
>>>> (a) a single coordinator to avoid the possibility of over-admitting
>>>> by different coordinators
>>>> (b) setting default query mem limits so that individual queries are
>>>> limited
>>>> For your scenario, I'd recommend setting up 2 pools, one for user A
>>>> and a second for user B. Set the max number of running queries for
>>>> user A to something reasonable for the concurrency for that workload.
>>>> Set the max memory for the user B pool to the portion of cluster
>>>> memory you're willing to give to those queries. (Notice the pool
>>>> with the small queries has the max number of running queries set and
>>>> the pool with the fewer but larger big queries has the max memory
>>>> set -- that is intentional, the former is faster for admission but
>>>> doesn't limit based on memory.) How well this will work depends on
>>>> how well you can pick good numbers for these settings, which can be
>>>> difficult and requires studying your workload.
>>>> This isn't perfect resource isolation because rogue queries can
>>>> still consume too much CPU or other resources, but it's the best
>>>> you'll be able to do right now. In the future we will have better
>>>> tools to make this easier.
>>>> Best,
>>>> Matt
>>>> On Mon, Jul 18, 2016 at 2:59 AM, 廖松博 <>
>>>>> Hello guys,
>>>>>        My Company is using Cloudera Impala as our basic
>>>>> infrastructure for online data analysis. The most difficult part we
>>>>> met is resource isolation and instability.
>>>>> According to our experiences in Impala, some big query which
>>>>> consume a vast amount of memory will crash impalad process(actually
>>>>> as worker but not coordinator, right?).
>>>>> In our simplest scenario, user A is a very important customer and
>>>>> his queries are relatively small, user B is a unimportant user who
>>>>> may issue very large SQL to impala. It is unacceptable that the big
>>>>> query from user B crash the impalad process and affect the user
>>>>> experiences of user A. So resource isolation is the point.
>>>>> But per the Impala documents :
>>>>> a _ admission.html , Impala resource isolation is soft limit,
>>>>> cannot strictly prevent query from user B affecting user A.
>>>>> As I know llama(run impala with yarn) is not recommended and we
>>>>> actually tried it but disappointed about the performance and accuracy.
>>>>>        Is there any best practice for user resource isolation? So
>>>>> different user will not affect each other.
>>>>>        Thanks.
>>>>> Best Regards,
>>>>> Songbo

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