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 <[email protected]<mailto:[email protected]>> Reply-To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Date: Tuesday, February 11, 2014 at 2:20 PM To: accumulo-user <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> Reply-To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Date: Tuesday, February 11, 2014 at 10:55 AM To: accumulo-user <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> 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
