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From James Hughes <jn...@virginia.edu>
Subject Re: Straggler problem in Accumulo BatchScans
Date Thu, 22 Aug 2013 14:13:47 GMT
David,

Have you tried the TableLoadBalancer?  I'd trying it before rolling your
own...  I think it should try to spread the tablets in your one table
across the tablet servers in a balanced way rather than balancing all of
the tablets for all tables across the nodes.

Other than that, I'd consider your key design and query plans.  If you are
routinely working with 0.5-5% of your data, I imagine things will be a
little slow in general...

Good luck!

Jim


On Wed, Aug 21, 2013 at 8:15 PM, <dlmarion@comcast.net> wrote:

> You can set it in the shell on the table. Just override the default tablet
> balancer for the table. I think the master has to use the Table load
> balancer also if it is not set by default.
>
> ------------------------------
> *From: *"David M. Slater" <David.Slater@jhuapl.edu>
> *To: *user@accumulo.apache.org
> *Sent: *Wednesday, August 21, 2013 8:12:46 PM
>
> *Subject: *RE: Straggler problem in Accumulo BatchScans
>
> Thanks Eric,
>
>
>
> Just to make sure I’m going in the right direction, this would involve
> extending the TabletBalancer class, correct? How do I add it to the table
> after that (and remove the old one)? I don’t see it under the Connector’s
> TableOperations().
>
>
>
> Is using a load-balancer what you would recommend if I wanted to make sure
> that two different tables stored related information (e.g. data and
> indexes) on the same tablets?
>
>
>
> Thanks,
> David
>
>
>
> *From:* Eric Newton [mailto:eric.newton@gmail.com]
> *Sent:* Wednesday, August 21, 2013 8:03 PM
> *To:* user@accumulo.apache.org
> *Subject:* Re: Straggler problem in Accumulo BatchScans
>
>
>
> A new balancer is a plug-in class that instructs the Master process where
> to place tablets.
>
>
>
> If you know you need your tablets spread out over servers based on time
> (row id), you can do that.  It's pretty common, in fact.
>
>
>
> -Eric
>
>
>
> On Wed, Aug 21, 2013 at 7:54 PM, Slater, David M. <David.Slater@jhuapl.edu>
> wrote:
>
> Hi Dave,
>
>
>
> The table is currently organizing netflow data with its rowID of
> timestamp_netflowRecordID, some columns corresponding to various netflow
> quantites, and one column representing the entire netflow in binary form.
>
>
>
> The table is about 1.2 TB, and I am scanning 5-40 GB per scan, which scans
> about 7-28 tablets.
>
>
>
> What do you mean by a custom load balancer? Do you mean balancing the data
> on ingest, or balancing the query load? What would you recommend for
> balancing the query load if I can only retrieve the data from a particular
> tablet?
>
>
>
> I’ve played with index/data caches, though I haven’t used readahead
> threads or max open files. Is that referring to rfiles?
>
>
>
> I’m noticing that most of the queries are CPU bound, and that read i/o is
> not being hit very hard. Is that a typical behavior for scans?
>
>
>
> Thanks,
> David
>
>
>
> *From:* Dave Marion [mailto:dlmarion@comcast.net]
>
> *Sent:* Wednesday, August 21, 2013 7:29 PM
> *To:* user@accumulo.apache.org
>
> *Subject:* RE: Straggler problem in Accumulo BatchScans
>
>
>
> How is the table organized?
>
> What percent of the table are you scanning in these large operations?
>
> Have you considered writing a custom load balancer?
>
>
>
> I don’t think that a tablet can be hosted on multiple servers. But you
> might be able to play around with the index/data caches, readahead threads
> (concurrent queries), and max open files to achieve better performance.
>
>
>
> *From:* Slater, David M. [mailto:David.Slater@jhuapl.edu<David.Slater@jhuapl.edu>]
>
> *Sent:* Wednesday, August 21, 2013 7:09 PM
> *To:* user@accumulo.apache.org
> *Subject:* Straggler problem in Accumulo BatchScans
>
>
>
> Hey, I have a 7 node network running accumulo 1.4.1 and hadoop 1.0.4.
>
>
>
> When I run large BatchScanner operations, the number of tablets scanned
> per node is not uniform, leading to the overloaded nodes taking much longer
> to finish than the others. For queries that require all of the scans to
> finish before returning, this is a major latency issue. What are some
> practical means of load-balancing this to reduce delay?
>
>
>
> Is it possible for tablets to be hosted on multiple tablet servers, up to
> the replication factor of the underlying hdfs? Are there reasons this might
> be an undesirable design?
>
>
>
> Thanks in advance,
> David
>
>
>
>

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