On Oct 14, 2014, at 10:34 AM, Gopal V <gop...@apache.org> wrote: > On 10/13/14, 10:53 PM, Sean McNamara wrote: > >> I’ve found a condition where the MemoryManager will wait too long before >> notifying writers >> to check their memory and flush. > ... >> This issue affects anyone who is writing a lot of columns, very large >> columns, or worst of >> all: both. I have tested and confirmed this issue on hive 0.12, 0.13, and >> trunk. > > Can you post the exact query, because this OOM is in my list of already fixed > performance issues (HIVE-6455). > > I have tested Hive-13 partitioned inserts with just "insert into table select > *" for both 30Tb of data and 10,000 columns.
https://issues.apache.org/jira/browse/HIVE-7250 adaptively chooses compression buffer size for ORC based on number of columns and available memory to further reduce memory pressure. This code path will kick-in only for >1000 columns. > > This issue happens in hive-12 & before, which keeps too many ORC files open > at the same time. > > If you are on hive-13 or later, setting the config option > hive.optimize.sort.dynamic.partition=true; should fix this issue. > > This follows a path within the FileSinkOperator which keeps exactly 1 stripe > open at any given time, so that the this always works correctly assuming the > orc.stripe.size fits within memory. > >> The issue is on line 50: ROWS_BETWEEN_CHECKS = 5000; >> >> For large or many columns it’s easy to hit GC issues or OOM before 5k rows >> are written. >> >> I believe that rows-between-checks should be made a configuration parameter >> that can be passed >> in on the JobConf. > > 5000 rows is probably the wrong thing to check, for sure - but it is a sane > default. Perhaps instead it could check between every stride index being > written (which is every 10,000 rows) or some fraction of it. > > But that check produces bad ORC files and still doesn't fix the actual issue > - this is merely postponing the inevitable. > > Let me describe the errors I hit before we had the sort.partition > implementation. > > At multiple terabyte scale, the next error you will hit will be an HDFS Lease > Expired exception, then the system runs out of file handles and after that it > runs of stack for DFSOutputStream threads. > > Even if you don't go that far, the memory manager doesn't slice memory all > the way down to a single row. The minimum size of a stripe is num-cols * > compress-size, we can't shrink the stripe size below that. > > The trouble is that with tiny stripes of less than 1Mb, the read-path suffers > heavily, the split generation becomes incredibly expensive and the > inter-stripe padding becomes a significant fraction of the HDFS space used > (upto 47% of space will be padding). > > So you can submit a patch for the JobConf to work around this, but it will > generate sub-optimal ORC files. > > The scalable & logically correct fix is already there in Hive, you have to > make sure the config option is on. > > FYI, the Hive plan we generate corresponds to an MRv2 example which combines > LazyOutputFormat with MultipleOutputs to produce similar results. > > Not sure if a similar option exists in Pig. > > Cheers, > Gopal -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
