Mark, As we discussed, it seems there is ~5X write amp on the system with 4K RW. Considering the amount of data going into rocksdb (and thus kicking of compaction so fast and degrading performance drastically) , it seems it is still writing WAL (?)..I used the following rocksdb option for faster background compaction as well hoping it can keep up with upcoming writes and writes won't be stalling. But, eventually, after a min or so, it is stalling io.. bluestore_rocksdb_options = "compression=kNoCompression,max_write_buffer_number=16,min_write_buffer_number_to_merge=3,recycle_log_file_num=16,compaction_style=kCompactionStyleLevel,write_buffer_size=67108864,target_file_size_base=67108864,max_background_compactions=31,level0_file_num_compaction_trigger=8,level0_slowdown_writes_trigger=32,level0_stop_writes_trigger=64,num_levels=4,max_bytes_for_level_base=536870912,max_bytes_for_level_multiplier=8,compaction_threads=32,flusher_threads=8" I will try to debug what is going on there.. Thanks & Regards Somnath -----Original Message----- From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel-owner@xxxxxxxxxxxxxxx] On Behalf Of Mark Nelson Sent: Thursday, June 09, 2016 6:46 AM To: Allen Samuels; Manavalan Krishnan; Ceph Development Subject: Re: RocksDB tuning On 06/09/2016 08:37 AM, Mark Nelson wrote: > Hi Allen, > > On a somewhat related note, I wanted to mention that I had forgotten > that chhabaremesh's min_alloc_size commit for different media types > was committed into master: > > https://github.com/ceph/ceph/commit/8185f2d356911274ca679614611dc335e3 > efd187 > > > IE those tests appear to already have been using a 4K min alloc size > due to non-rotational NVMe media. I went back and verified that > explicitly changing the min_alloc size (in fact all of them to be > sure) to 4k does not change the behavior from graphs I showed > yesterday. The rocksdb compaction stalls due to excessive reads > appear (at least on the > surface) to be due to metadata traffic during heavy small random writes. Sorry, this was worded poorly. Traffic due to compaction of metadata (ie not leaked WAL data) during small random writes. Mark > > Mark > > On 06/08/2016 06:52 PM, Allen Samuels wrote: >> Let's make a patch that creates actual Ceph parameters for these >> things so that we don't have to edit the source code in the future. >> >> >> Allen Samuels >> SanDisk |a Western Digital brand >> 2880 Junction Avenue, San Jose, CA 95134 >> T: +1 408 801 7030| M: +1 408 780 6416 allen.samuels@xxxxxxxxxxx >> >> >>> -----Original Message----- >>> From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel- >>> owner@xxxxxxxxxxxxxxx] On Behalf Of Manavalan Krishnan >>> Sent: Wednesday, June 08, 2016 3:10 PM >>> To: Mark Nelson <mnelson@xxxxxxxxxx>; Ceph Development <ceph- >>> devel@xxxxxxxxxxxxxxx> >>> Subject: RocksDB tuning >>> >>> Hi Mark >>> >>> Here are the tunings that we used to avoid the IOPs choppiness caused by >>> rocksdb compaction. >>> >>> We need to add the following options in src/kv/RocksDBStore.cc before >>> rocksdb::DB::Open in RocksDBStore::do_open opt.IncreaseParallelism(16); >>> opt.OptimizeLevelStyleCompaction(512 * 1024 * 1024); >>> >>> >>> >>> Thanks >>> Mana >>> >>> >>>> >>> >>> PLEASE NOTE: The information contained in this electronic mail >>> message is >>> intended only for the use of the designated recipient(s) named above. >>> If the >>> reader of this message is not the intended recipient, you are hereby >>> notified >>> that you have received this message in error and that any review, >>> dissemination, distribution, or copying of this message is strictly >>> prohibited. 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