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From Kesten Broughton <kbrough...@21ct.com>
Subject Re: ingest problems
Date Wed, 12 Feb 2014 17:36:28 GMT
we are now pre-splitting data for ingest.  Still seeing the error that morgan mentioned in
q. 8 response to Sean Busbey


From: David Medinets <david.medinets@gmail.com<mailto:david.medinets@gmail.com>>
Reply-To: "user@accumulo.apache.org<mailto:user@accumulo.apache.org>" <user@accumulo.apache.org<mailto:user@accumulo.apache.org>>
Date: Tuesday, February 11, 2014 at 2:20 PM
To: accumulo-user <user@accumulo.apache.org<mailto:user@accumulo.apache.org>>
Subject: Re: ingest problems

In your example, the row ID is "000c35b2-ee6c-339e-9e6a-65a9bccbfa2c". If you are using one
UUID
for all of the ingested data, then you'd be creating one large row and just one tablet would
be ingesting the information.

If you are using more than one UUID in the row fields, are you pre-splitting the accumulo
table before the ingest process?



On Tue, Feb 11, 2014 at 3:08 PM, Keith Turner <keith@deenlo.com<mailto:keith@deenlo.com>>
wrote:
When you add edges are you by chance creating one mutation and adding a lot of edges to it?
  This could create a large mutation, which would have to fit in JVM memory on the tserver
(which looks like its 1g).

Accumulo logs messages about whats going on w/ the java GC every few seconds.   Try grepping
the tserver logs for GC, what does this look like?


On Tue, Feb 11, 2014 at 2:23 PM, Kesten Broughton <kbroughton@21ct.com<mailto:kbroughton@21ct.com>>
wrote:
Hi david,

Responses inline


What is the average load on the servers while the ingest runs?

We are seeing ingest rates (ingest column on accumulo dashboard) of 200-400k.  Load is low,
perhaps up to 1 on a 4 core vm.  Less on bare-metal.  Often we see only one tablet server
(of two) ingesting.  However, both show they are online.  Sometimes it is just highly skewed.
 We are now running pre-split ingests.

How large are the mutations?

How do we determine this?

What are your heap sizes?

Typically we are running with configs based on the example 2Gb accumulo-site.xml.  Our block
count is under 2000.   See config bundle for more details.

How much memory do the servers have?

metal hdfs cluster - 256 Gb, 2nd metal cluster - 128 Gb, virtual boxes - 16Gb

Can you move beyond a three node cluster?

We are moving to this now.   ETA 2 days for virtualized stack of 9 nodes, 8 core, 64 Gb, fully
separating 3 zookeepers, master nodes and 3 datanodes.  ETA for metal version of this 1-2
weeks.

Are you querying while writing to the same table?

No

[http://portal.mxlogic.com/images/transparent.gif]|

From: David Medinets <david.medinets@gmail.com<mailto:david.medinets@gmail.com>>
Reply-To: "user@accumulo.apache.org<mailto:user@accumulo.apache.org>" <user@accumulo.apache.org<mailto:user@accumulo.apache.org>>
Date: Tuesday, February 11, 2014 at 10:55 AM
To: accumulo-user <user@accumulo.apache.org<mailto:user@accumulo.apache.org>>
Subject: Re: ingest problems

My cluster ingests data every night. We use a map-reduce program to generate rFiles. Then
import those files into Accumulo. No hiccups. No instability. I've also used map-reduce to
directly write mutations. Haven't seen any issues there either.

What is the average load on the servers while the ingest runs?
How large are the mutations?
What are your heap sizes?
How much memory do the servers have?
Can you move beyond a three node cluster?
Are you querying while writing to the same table?



On Tue, Feb 11, 2014 at 11:28 AM, Josh Elser <josh.elser@gmail.com<mailto:josh.elser@gmail.com>>
wrote:
On 2/11/14, 11:10 AM, Kesten Broughton wrote:
Hi there,

We have been experimenting with accumulo for about two months now.  Our
biggest painpoint has been on ingest.
Often we will have ingest process fail 2 or 3 times 3/4 of the way
through an ingest and then on a final try it works, without any changes.

Funny, most times I hear that people consider Accumulo to handles ingest fairly well, but
let's see what we can do to help.

We need a bit more information than what you provided here though: what's your "ingest process"?
Are you using some other workflow library? Are you running MapReduce? Do you just have a Java
class with a main method that uses a BatchWriter?

The fact that it "works sometimes" implies that the problem might be resource related.


Once the ingest works, the cluster is usually stable for querying for
weeks or months only requiring the occasional start-all.sh if there is a
problem.

Sometimes our ingest can be 24 hours long, and we need a stronger ingest
story to be able to commit to accumulo.

You should be able to run ingest 24/7 with Accumulo without it falling over (I do regularly
to stress-test it). The limitation should only be the disk-space you have available.


Our cluster architecture has been:
3 hdfs datanodes overlaid with name node, secondary nn and accumulo
master each collocated with a datanode, and a zookeeper server on each.
We realize this is not optimal and are transitioning to separate
hardware for zookeepers and name/secondary/accumulomaster nodes.
However, the big concern is that sometimes a failed ingest will bork the
whole cluster and we have to re-init accumulo with an accumulo init
destroying all our data.
We have experienced this on at least three different clusters of this
description.

Can you be more specific than "bork the whole cluster"? Unless you're hitting a really nasty
bug, there shouldn't be any way that a client writing data into Accumulo will destroy an instance.


The most recent attempt was on a 65GB dataset.   The cluster had been up
for over 24 hours.  The ingest test takes 40 mins and about 5 mins
in, one of the datanodes failed.
There were no error logs on the failed node, and the two other nodes had
logs filled with zookeeper connection errors.  We were unable to recover
the cluster and had to re-init.

Check both the log4j logs and the stdout/stderr redirection files for the datanode process.
Typically, if you get an OOME, log4j gets torn down before that exception can be printed to
the normal log files. "Silent" failures seem indicative of lack of physical resources (over-subscribed
the node) on the box or insufficient resources provided to the processes (-Xmx was too small
for the process).


I know a vague description of problems is difficult to respond to, and
the next time we have an ingest failure, i will bring specifics forward.
  But I’m writing to know if
1.  Ingest failures are a known fail point for accumulo, or if we are
perhaps unlucky/mis-configured.

No -- something else is going on here.


2.  Are there any guidelines for capturing ingest failures / determining
root causes when errors don’t show up in the logs

For any help request, be sure to gather Accumulo, Hadoop and ZooKeeper versions, OS and Java
versions. Capturing log files and stdout/stderr files are important; beware that if you restart
the Accumulo process on that node, it will overwrite the stdout/stderr files, so make sure
to copy them out of the way.


3.  Are there any means of checkpointing a data ingest, so that if a
failure were to occur at hour 23.5 we could roll back to hour 23 and
continue.  Client code could checkpoint and restart at the last one, but
if the underlying accumulo cluster can’t be recovered, that’s of no use.

You can do anything you want in your client ingest code :)

Assuming that you're using a BatchWriter, if you manually call flush() and it returns without
Exception, you can assume that all data up to that point written with that BatchWriter instance
is "ingested". This can easily extrapolated: if you're ingesting CSV files, ensure that a
flush() happens every 1000lines and denote that somewhere that your ingest process can advance
itself to the appropriate place in the CSV file and proceed from where it left off.

thanks,

kesten




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