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From Konstantinos Kougios <kostas.koug...@googlemail.com>
Subject Re: does phoenix+hbase work for tables larger than a few GB?
Date Wed, 30 Sep 2015 22:29:34 GMT
Thanks for the reply and the useful information Anil.

I am aware of the difficulties of distributed joins and aggregations and 
that phoenix is a layer on top of hbase. It would be great if it could 
be configured to run the queries, even if it takes a lot of time for the 
queries to complete.

I got mainly 2 tables of 170GB and 550GB. Aggregation queries on both 
fail and even make region servers crash (there is no info in the logs 
and still don't know why. My server proved to be rock stable so far on 
other things but you never know).

I am doing full table scans only because so far I was unable to create 
the indexes. I tried async indexes too with the map reduce job to create 
them but it runs extremely slowly.

In theory full table scans are possible with hbase, so even if it was 
slow it shouldn't fail.

My setup is a 64GB AMD opteron server with 16 cores. 3 lxc virtual 
machines as region servers with Xmx8G, each running on a 3TB 7200rpm 
disk. So somehow I simulate 3x low spec servers with enough ram.

Next thing I will try is give region servers 16GB of RAM. WIth 8GB they 
seem to have some memory pressure and I see some slow GC's in the logs.

Cheers




On 30/09/15 21:18, anil gupta wrote:
> Hi Konstantinos,
> Please find my reply inline.
>
> On Wed, Sep 30, 2015 at 12:10 PM, Konstantinos Kougios 
> <kostas.kougios@googlemail.com <mailto:kostas.kougios@googlemail.com>> 
> wrote:
>
>     Hi all,
>
>     I had various issues with big tables while experimenting the
>     couple last weeks.
>
>     The thing that goes to my mind is that hbase (+phoenix) works only
>     when there is a fairly powerful cluster and say 1/2 the data can
>     fit into the combined servers memory and disks are fast (SSD?) as
>     well. It doesn't seem to be able to work when tables are 2x as
>     large as the memory allocated to region servers (frankly I think
>     it is less)
>
> Anil: Phoenix is just a SQL layer over HBase. From the query in your 
> previous emails, it seems like you are doing full table scans with 
> group by clauses. IMO, HBase is not a DB to be used for full table 
> scans. If 90% of your use cases are small range scan or gets then 
> HBase should work nicely with Terabytes of data. I have a 40 TB table 
> in prod on 60 node cluster where every RS only has 16GB of heap. What 
> kind of workload you are trying to run with HBase?
>
>
>     Things that constantly fail:
>
>     - non-trivial queries on large tables (with group by, counts,
>     joins) with region server out of memory errors or crashes without
>     any reason for Xmx of 4G or 8G
>
> Anil: Can you convert these queries into short range based scans? If 
> you are always going to do full table scan, then maybe you need to use 
> MR or Spark for those computation and then tune cluster for full table 
> scans. Cluster tuning varies with full table scan workload.
>
>     - index creation on the same big tables. Those always fail I think
>     around the point when hbase has to flush it's memory regions to
>     the disk and couldn't find a solution
>
>     - spark jobs fail unless they are throttled to feed hbase with the
>     data it can take . No backpressure?
>
>
>     There were no replies to my emails regarding the issues, which
>     makes me think there aren't solutions (or solutions are pretty
>     hard to find and not many ppl know them).
>
>     So after 21 tweaks to the default config, I am still not able to
>     operate it as a normal database.
>
> Anil: HBase is actually not a normal RDBMS DB. Its a **keyvalue 
> store**. Phoenix is providing a SQL layer using HBase API. So, user 
> will need to deal with pros/cons of a key/value store.
>
>
>     Should I start believing my config is all wrong or that
>     hbase+phoenix is only working if there is a sufficiently powerful
>     cluster to handle the data?
>
> Anil: **As per my experience**, HBase+Phoenix will work nicely if you 
> are doing keyvalue lookups and short range scans.
> I would suggest you to evaluate data model of HBase tables and try to 
> convert queries to small range scan or lookups.
>
>
>     I believe it is a great project and the functionality is really
>     useful. What's lacking is 3 sample configs for 3 different
>     strength clusters.
>
> Anil: I agree that guidance on configuration of HBase and Phoenix can 
> be improved so that people can get going quickly.
>
>
>     Thanks
>
>
>
>
> -- 
> Thanks & Regards,
> Anil Gupta


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