I don’t think it will work without HDFS. Mohammed
From: Wang, Ningjun (LNG-NPV) [mailto:ningjun.w...@lexisnexis.com] Sent: Tuesday, January 20, 2015 7:55 AM To: Wang, Ningjun (LNG-NPV) Cc: user@spark.apache.org Subject: RE: Can I save RDD to local file system and then read it back on spark cluster with multiple nodes? Can anybody answer this? Do I have to have hdfs to achieve this? Regards, Ningjun Wang Consulting Software Engineer LexisNexis 121 Chanlon Road New Providence, NJ 07974-1541 From: Wang, Ningjun (LNG-NPV) [mailto:ningjun.w...@lexisnexis.com] Sent: Friday, January 16, 2015 1:15 PM To: Imran Rashid Cc: user@spark.apache.org<mailto:user@spark.apache.org> Subject: RE: Can I save RDD to local file system and then read it back on spark cluster with multiple nodes? I need to save RDD to file system and then restore my RDD from the file system in the future. I don’t have any hdfs file system and don’t want to go the hassle of setting up a hdfs system. So how can I achieve this? The application need to be run on a cluster with multiple nodes. Regards, Ningjun From: imranra...@gmail.com<mailto:imranra...@gmail.com> [mailto:imranra...@gmail.com] On Behalf Of Imran Rashid Sent: Friday, January 16, 2015 12:14 PM To: Wang, Ningjun (LNG-NPV) Cc: user@spark.apache.org<mailto:user@spark.apache.org> Subject: Re: Can I save RDD to local file system and then read it back on spark cluster with multiple nodes? I'm not positive, but I think this is very unlikely to work. First, when you call sc.objectFile(...), I think the *driver* will need to know something about the file, eg to know how many tasks to create. But it won't even be able to see the file, since it only lives on the local filesystem of the cluster nodes. If you really wanted to, you could probably write out some small metadata about the files and write your own version of objectFile that uses it. But I think there is a bigger conceptual issue. You might not in general be sure that you are running on the same nodes when you save the file, as when you read it back in. So the file might not be present on the local filesystem for the active executors. You might be able to guarantee it for the specific cluster setup you have now, but it might limit you down the road. What are you trying to achieve? There might be a better way. I believe writing to hdfs will usually write one local copy, so you'd still be doing a local read when you reload the data. Imran On Jan 16, 2015 6:19 AM, "Wang, Ningjun (LNG-NPV)" <ningjun.w...@lexisnexis.com<mailto:ningjun.w...@lexisnexis.com>> wrote: I have asked this question before but get no answer. Asking again. Can I save RDD to the local file system and then read it back on a spark cluster with multiple nodes? rdd.saveAsObjectFile(“file:///home/data/rdd1<file:///\\home\data\rdd1>”) val rdd2 = sc.objectFile(“file:///home/data/rdd1<file:///\\home\data\rdd1>”) This will works if the cluster has only one node. But my cluster has 3 nodes and each node has a local dir called /home/data. Is rdd saved to the local dir across 3 nodes? If so, does sc.objectFile(…) smart enough to read the local dir in all 3 nodes to merge them into a single rdd? Ningjun
