For default object size I see ~24K worst case onode size. Somnath is using 1M object, so onode size should be ~24K/4 = ~6K. On 6/10/16, 9:51 AM, "ceph-devel-owner@xxxxxxxxxxxxxxx on behalf of Igor Fedotov" <ceph-devel-owner@xxxxxxxxxxxxxxx on behalf of ifedotov@xxxxxxxxxxxx> wrote: >An update: > >I found that my previous results were invalid - SyntheticWorkloadState >had an odd swap for offset > len case... Made a brief fix. > >Now onode size with csum raises up to 38K, without csum - 28K. > >For csum case there is 350 lextents and about 170 blobs > >For no csum - 343 lextents and about 170 blobs. > >(blobs counting is very inaccurate!) > >Potentially we shouldn't have >64 blobs per 4M thus looks like some >issues in the write path... > >And CSum vs. NoCsum differenct looks pretty consistent - 170 blobs * 4 >byte * 16 values = 10880 > >Branch's @github been updated with corresponding fixes. > >Thanks, >Igor. > >On 10.06.2016 19:06, Allen Samuels wrote: >> Let's see, 4MB is 2^22 bytes. If we storage a checksum for each 2^12 >>bytes that's 2^10 checksums at 2^2 bytes each is 2^12 bytes. >> >> So with optimal encoding, the checksum baggage shouldn't be more than >>4KB per oNode. >> >> But you're seeing 13K as the upper bound on the onode size. >> >> In the worst case, you'll need at least another block address (8 bytes >>currently) and length (another 8 bytes) [though as I point out, the >>length is something that can be optimized out] So worst case, this >>encoding would be an addition 16KB per onode. >> >> I suspect you're not at the worst-case yet :) >> >> Allen Samuels >> SanDisk |a Western Digital brand >> 2880 Junction Avenue, Milpitas, CA 95134 >> T: +1 408 801 7030| M: +1 408 780 6416 >> allen.samuels@xxxxxxxxxxx >> >> >>> -----Original Message----- >>> From: Igor Fedotov [mailto:ifedotov@xxxxxxxxxxxx] >>> Sent: Friday, June 10, 2016 8:58 AM >>> To: Sage Weil <sweil@xxxxxxxxxx>; Somnath Roy >>> <Somnath.Roy@xxxxxxxxxxx> >>> Cc: Allen Samuels <Allen.Samuels@xxxxxxxxxxx>; Mark Nelson >>> <mnelson@xxxxxxxxxx>; Manavalan Krishnan >>> <Manavalan.Krishnan@xxxxxxxxxxx>; Ceph Development <ceph- >>> devel@xxxxxxxxxxxxxxx> >>> Subject: Re: RocksDB tuning >>> >>> Just modified store_test synthetic test case to simulate many random 4K >>> writes to 4M object. >>> >>> With default settings ( crc32c + 4K block) onode size varies from 2K >>>to ~13K >>> >>> with disabled crc it's ~500 - 1300 bytes. >>> >>> >>> Hence the root cause seems to be in csum array. >>> >>> >>> Here is the updated branch: >>> >>> https://github.com/ifed01/ceph/tree/wip-bluestore-test-size >>> >>> >>> Thanks, >>> >>> Igor >>> >>> >>> On 10.06.2016 18:40, Sage Weil wrote: >>>> On Fri, 10 Jun 2016, Somnath Roy wrote: >>>>> Just turning off checksum with the below param is not helping, I >>>>> still need to see the onode size though by enabling debug..Do I need >>>>> to mkfs >>>>> (Sage?) as it is still holding checksum of old data I wrote ? >>>> Yeah.. you'll need to mkfs to blow away the old onodes and blobs with >>>> csum data. >>>> >>>> As Allen pointed out, this is only part of the problem.. but I'm >>>> curious how much! >>>> >>>>> bluestore_csum = false >>>>> bluestore_csum_type = none >>>>> >>>>> Here is the snippet of 'dstat'.. >>>>> >>>>> ----total-cpu-usage---- -dsk/total- -net/total- ---paging--> >>>>> usr sys idl wai hiq siq| read writ| recv send| in out > >>>>> 41 14 36 5 0 4| 138M 841M| 212M 145M| 0 0 > >>>>> 42 14 35 5 0 4| 137M 855M| 213M 147M| 0 0 > >>>>> 40 14 38 5 0 3| 143M 815M| 209M 144M| 0 0 > >>>>> 40 14 38 5 0 3| 137M 933M| 194M 134M| 0 0 > >>>>> 42 15 34 5 0 4| 133M 918M| 220M 151M| 0 0 > >>>>> 35 13 43 6 0 3| 147M 788M| 194M 134M| 0 0 > >>>>> 31 11 49 6 0 3| 157M 713M| 151M 104M| 0 0 > >>>>> 39 14 38 5 0 4| 139M 836M| 246M 169M| 0 0 > >>>>> 40 14 38 5 0 3| 139M 845M| 204M 140M| 0 0 > >>>>> 40 14 37 5 0 4| 149M 743M| 210M 144M| 0 0 > >>>>> 42 14 35 5 0 4| 143M 852M| 216M 150M| 0 0 > >>>>> For example, what last entry is saying that system (with 8 osds) is >>> receiving 216M of data over network and in response to that it is >>>writing total >>> of 852M of data and reading 143M of data. At this time FIO on client >>>side is >>> reporting ~35K 4K RW iops. >>>>> Now, after a min or so, the throughput goes down to barely 1K from >>>>>FIO >>> (and very bumpy) and here is the 'dstat' snippet at that time.. >>>>> ----total-cpu-usage---- -dsk/total- -net/total- ---paging--> >>>>> usr sys idl wai hiq siq| read writ| recv send| in out > >>>>> 2 1 83 14 0 0| 220M 58M|4346k 3002k| 0 0 > >>>>> 2 1 82 14 0 0| 223M 60M|4050k 2919k| 0 0 > >>>>> 3 1 82 13 0 0| 217M 63M|6403k 4306k| 0 0 > >>>>> 2 1 83 14 0 0| 226M 54M|2126k 1497k| 0 0 > >>>>> >>>>> So, system is barely receiving anything (~2M) but still writing ~54M >>>>>of data >>> and reading 226M of data from disk. >>>>> After killing fio script , here is the 'dstat' output.. >>>>> >>>>> ----total-cpu-usage---- -dsk/total- -net/total- ---paging--> >>>>> usr sys idl wai hiq siq| read writ| recv send| in out > >>>>> 2 1 86 12 0 0| 186M 66M| 28k 26k| 0 0 > >>>>> 2 1 86 12 0 0| 201M 78M| 20k 21k| 0 0 > >>>>> 2 1 85 12 0 0| 230M 100M| 24k 24k| 0 0 > >>>>> 2 1 85 12 0 0| 206M 78M| 21k 20k| 0 0 > >>>>> >>>>> Not receiving anything from client but still writing 78M of data and >>>>>206M >>> of read. >>>>> Clearly, it is an effect of rocksdb compaction that stalling IO and >>>>>even if we >>> increased compaction thread (and other tuning), compaction is not able >>>to >>> keep up with incoming IO. >>>>> Thanks & Regards >>>>> Somnath >>>>> >>>>> -----Original Message----- >>>>> From: Allen Samuels >>>>> Sent: Friday, June 10, 2016 8:06 AM >>>>> To: Sage Weil >>>>> Cc: Somnath Roy; Mark Nelson; Manavalan Krishnan; Ceph Development >>>>> Subject: RE: RocksDB tuning >>>>> >>>>>> -----Original Message----- >>>>>> From: Sage Weil [mailto:sweil@xxxxxxxxxx] >>>>>> Sent: Friday, June 10, 2016 7:55 AM >>>>>> To: Allen Samuels <Allen.Samuels@xxxxxxxxxxx> >>>>>> Cc: Somnath Roy <Somnath.Roy@xxxxxxxxxxx>; Mark Nelson >>>>>> <mnelson@xxxxxxxxxx>; Manavalan Krishnan >>>>>> <Manavalan.Krishnan@xxxxxxxxxxx>; Ceph Development <ceph- >>>>>> devel@xxxxxxxxxxxxxxx> >>>>>> Subject: RE: RocksDB tuning >>>>>> >>>>>> On Fri, 10 Jun 2016, Allen Samuels wrote: >>>>>>> Checksums are definitely a part of the problem, but I suspect the >>>>>>> smaller part of the problem. This particular use-case (random 4K >>>>>>> overwrites without the WAL stuff) is the worst-case from an >>>>>>> encoding perspective and highlights the inefficiency in the current >>> code. >>>>>>> As has been discussed earlier, a specialized encode/decode >>>>>>> implementation for these data structures is clearly called for. >>>>>>> >>>>>>> IMO, you'll be able to cut the size of this by AT LEAST a factor of >>>>>>> 3 or >>>>>>> 4 without a lot of effort. The price will be somewhat increase CPU >>>>>>> cost for the serialize/deserialize operation. >>>>>>> >>>>>>> If you think of this as an application-specific data compression >>>>>>> problem, here is a short list of potential compression >>>>>>>opportunities. >>>>>>> >>>>>>> (1) Encoded sizes and offsets are 8-byte byte values, converting >>>>>>> these too >>>>>> block values will drop 9 or 12 bits from each value. Also, the >>>>>> ranges for these values is usually only 2^22 -- often much less. >>>>>> Meaning that there's 3-5 bytes of zeros at the top of each word >>>>>>that can >>> be dropped. >>>>>>> (2) Encoded device addresses are often less than 2^32, meaning >>>>>>> there's 3-4 >>>>>> bytes of zeros at the top of each word that can be dropped. >>>>>>> (3) Encoded offsets and sizes are often exactly "1" block, >>>>>>>clever >>>>>>> choices of >>>>>> formatting can eliminate these entirely. >>>>>>> IMO, an optimized encoded form of the extent table will be around >>>>>>> 1/4 of the current encoding (for this use-case) and will likely >>>>>>> result in an Onode that's only 1/3 of the size that Somnath is >>>>>>>seeing. >>>>>> That will be true for the lextent and blob extent maps. I'm >>>>>> guessing this is a small part of the ~5K somnath saw. If his >>>>>> objects are 4MB then 4KB of it >>>>>> (80%) is the csum_data vector, which is a flat vector of >>>>>> u32 values that are presumably not very compressible. >>>>> I don't think that's what Somnath is seeing (obviously some data >>>>>here will >>> sharpen up our speculations). But in his use case, I believe that he >>>has a >>> separate blob and pextent for each 4K write (since it's been subjected >>>to >>> random 4K overwrites), that means somewhere in the data structures at >>> least one address and one length for each of the 4K blocks (and likely >>>much >>> more in the lextent and blob maps as you alluded to above). The >>>encoding of >>> just this information alone is larger than the checksum data. >>>>>> We could perhaps break these into a separate key or keyspace.. >>>>>> That'll give rocksdb a bit more computation work to do (for a custom >>>>>> merge operator, probably, to update just a piece of the value) but >>>>>> for a 4KB value I'm not sure it's big enough to really help. Also >>>>>> we'd lose locality, would need a second get to load csum metadata on >>> read, etc. >>>>>> :/ I don't really have any good ideas here. >>>>>> >>>>>> sage >>>>>> >>>>>> >>>>>>> Allen Samuels >>>>>>> SanDisk |a Western Digital brand >>>>>>> 2880 Junction Avenue, Milpitas, CA 95134 >>>>>>> T: +1 408 801 7030| M: +1 408 780 6416 allen.samuels@xxxxxxxxxxx >>>>>>> >>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: Sage Weil [mailto:sweil@xxxxxxxxxx] >>>>>>>> Sent: Friday, June 10, 2016 2:35 AM >>>>>>>> To: Somnath Roy <Somnath.Roy@xxxxxxxxxxx> >>>>>>>> Cc: Mark Nelson <mnelson@xxxxxxxxxx>; Allen Samuels >>>>>>>> <Allen.Samuels@xxxxxxxxxxx>; Manavalan Krishnan >>>>>>>> <Manavalan.Krishnan@xxxxxxxxxxx>; Ceph Development <ceph- >>>>>>>> devel@xxxxxxxxxxxxxxx> >>>>>>>> Subject: RE: RocksDB tuning >>>>>>>> >>>>>>>> On Fri, 10 Jun 2016, Somnath Roy wrote: >>>>>>>>> Sage/Mark, >>>>>>>>> I debugged the code and it seems there is no WAL write going on >>>>>>>>> and >>>>>>>> working as expected. But, in the process, I found that onode size >>>>>>>> it is >>>>>> writing >>>>>>>> to my environment ~7K !! See this debug print. >>>>>>>>> 2016-06-09 15:49:24.710149 7f7732fe3700 20 >>>>>>>> bluestore(/var/lib/ceph/osd/ceph-0) onode >>>>>>>> #1:7d3c6423:::rbd_data.10186b8b4567.0000000000070cd4:head# is >>> 7518 >>>>>>>>> This explains why so much data going to rocksdb I guess. Once >>>>>>>>> compaction kicks in iops I am getting is *30 times* slower. >>>>>>>>> >>>>>>>>> I have 15 osds on 8TB drives and I have created 4TB rbd image >>>>>>>>> preconditioned with 1M. I was running 4K RW test. >>>>>>>> The onode is big because of the csum metdata. Try setting >>>>>>>> 'bluestore >>>>>> csum >>>>>>>> type = none' and see if that is the entire reason or if something >>>>>>>> else is >>>>>> going >>>>>>>> on. >>>>>>>> >>>>>>>> We may need to reconsider the way this is stored. >>>>>>>> >>>>>>>> s >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> Thanks & Regards >>>>>>>>> Somnath >>>>>>>>> >>>>>>>>> -----Original Message----- >>>>>>>>> From: ceph-devel-owner@xxxxxxxxxxxxxxx >>>>>>>>> [mailto:ceph-devel-owner@xxxxxxxxxxxxxxx] On Behalf Of Somnath >>>>>> Roy >>>>>>>>> Sent: Thursday, June 09, 2016 8:23 AM >>>>>>>>> To: Mark Nelson; Allen Samuels; Manavalan Krishnan; Ceph >>>>>> Development >>>>>>>>> Subject: RE: RocksDB tuning >>>>>>>>> >>>>>>>>> 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=k >>>>>> CompactionStyleLevel,write_buffer_size=67108864,target_file_size_bas >>>>>> e=6 >>>>>> >>> 7108864,max_background_compactions=31,level0_file_num_compaction_tri >>> gger=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/8185f2d356911274ca679614611dc335 >>>>>>>>>> e3 >>>>>>>>>> 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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