You might want to look at this follow up work as well: https://www.usenix.org/conference/osdi16/technical-sessions/presentation/alagappan
It talks about how to use bob on distributed systems. On Sun, Apr 2, 2017 at 4:32 PM, Ted Yu <[email protected]> wrote: > Need some time to digest the BOB and see if it can simplify the reasoning > of how fsync is implemented in hbase. > > hdfs was evaluated by the paper where I noticed the following: > > bq. both HDFS and ZooKeeper respondents lament that such an fsync() is not > easily achievable with Java > > Cheers > > On Sun, Apr 2, 2017 at 1:53 PM, 杨苏立 Yang Su Li <[email protected]> wrote: > > > Regarding HBASE-5954 specifically, have you thought about using BOB > (block > > order breaker, > > https://www.usenix.org/system/files/conference/osdi14/ > > osdi14-paper-pillai.pdf) > > to verify if a change is correct. > > > > It allows you to explore many different crash scenarios. > > > > > > > > On Sun, Apr 2, 2017 at 1:35 PM, 杨苏立 Yang Su Li <[email protected]> > wrote: > > > > > I understand why HBase by default does not use hsync -- it does come > with > > > big performance cost (though for FSYNC_WAL which is not the default > > option, > > > you should probably do it because the documentation explicitly promised > > > it). > > > > > > > > > I just want to make sure my description about HBase is accurate, > > including > > > the durability aspect. > > > > > > On Sun, Apr 2, 2017 at 12:19 PM, Ted Yu <[email protected]> wrote: > > > > > >> Suli: > > >> Have you looked at HBASE-5954 ? > > >> > > >> It gives some background on why hbase code is formulated the way it > > >> currently is. > > >> > > >> Cheers > > >> > > >> On Sun, Apr 2, 2017 at 9:36 AM, 杨苏立 Yang Su Li <[email protected]> > > >> wrote: > > >> > > >> > Don't your second paragraph just prove my point? -- If data is not > > >> > persisted to disk, then it is not durable. That is the definition of > > >> > durability. > > >> > > > >> > If you want the data to be durable, then you need to call hsync() > > >> instead > > >> > of hflush(), and that would be the correct behavior if you use > > FSYNC_WAL > > >> > flag (per HBase documentation). > > >> > > > >> > However, HBase does not do that. > > >> > > > >> > Suli > > >> > > > >> > On Sun, Apr 2, 2017 at 11:26 AM, Josh Elser <[email protected]> > > >> wrote: > > >> > > > >> > > No, that's not correct. HBase would, by definition, not be a > > >> > > consistent database if a write was not durable when a client sees > a > > >> > > successful write. > > >> > > > > >> > > The point that I will concede to you is that the hflush call may, > in > > >> > > extenuating circumstances, may not be completely durable. For > > example, > > >> > > HFlush does not actually force the data to disk. If an abrupt > power > > >> > > failure happens before this data is pushed to disk, HBase may > think > > >> > > that data was durable when it actually wasn't (at the HDFS level). > > >> > > > > >> > > On Thu, Mar 30, 2017 at 4:26 PM, 杨苏立 Yang Su Li < > [email protected] > > > > > >> > > wrote: > > >> > > > Also, please correct me if I am wrong, but I don't think a put > is > > >> > durable > > >> > > > when an RPC returns to the client. Just its corresponding WAL > > entry > > >> is > > >> > > > pushed to the memory of all three data nodes, so it has a low > > >> > probability > > >> > > > of being lost. But nothing is persisted at this point. > > >> > > > > > >> > > > And this is true no mater you use SYNC_WAL or FSYNC_WAL flag. > > >> > > > > > >> > > > On Tue, Mar 28, 2017 at 12:11 PM, Josh Elser <[email protected] > > > > >> > wrote: > > >> > > > > > >> > > >> 1.1 -> 2: don't forget about the block cache which can > invalidate > > >> the > > >> > > need > > >> > > >> for any HDFS read. > > >> > > >> > > >> > > >> I think you're over-simplifying the write-path quite a bit. I'm > > not > > >> > sure > > >> > > >> what you mean by an 'asynchronous write', but that doesn't > exist > > at > > >> > the > > >> > > >> HBase RPC layer as that would invalidate the consistency > > guarantees > > >> > (if > > >> > > an > > >> > > >> RPC returns to the client that data was "put", then it is > > durable). > > >> > > >> > > >> > > >> Going off of memory (sorry in advance if I misstate something): > > the > > >> > > >> general way that data is written to the WAL is a "group > commit". > > >> You > > >> > > have > > >> > > >> many threads all trying to append data to the WAL -- > performance > > >> would > > >> > > be > > >> > > >> terrible if you serially applied all of these writes. Instead, > > many > > >> > > writes > > >> > > >> can be accepted and a the caller receives a Future. The caller > > must > > >> > wait > > >> > > >> for the Future to complete. What's happening behind the scene > is > > >> that > > >> > > the > > >> > > >> writes are being bundled together to reduce the number of syncs > > to > > >> the > > >> > > WAL > > >> > > >> ("grouping" the writes together). When one caller's future > would > > >> > > complete, > > >> > > >> what really happened is that the write/sync which included the > > >> > caller's > > >> > > >> update was committed (along with others). All of this is > > happening > > >> > > inside > > >> > > >> the RS's implementation of accepting an update. > > >> > > >> > > >> > > >> https://github.com/apache/hbase/blob/55d6dcaf877cc5223e67973 > > >> > > >> 6eb613173229c18be/hbase-server/src/main/java/org/apache/ > > >> hadoop/hbase/ > > >> > > >> regionserver/wal/FSHLog.java#L74-L106 > > >> > > >> > > >> > > >> > > >> > > >> 杨苏立 Yang Su Li wrote: > > >> > > >> > > >> > > >>> The attachment can be found in the following URL: > > >> > > >>> http://pages.cs.wisc.edu/~suli/hbase.pdf > > >> > > >>> > > >> > > >>> Sorry for the inconvenience... > > >> > > >>> > > >> > > >>> > > >> > > >>> On Mon, Mar 27, 2017 at 8:25 PM, Ted Yu<[email protected]> > > >> wrote: > > >> > > >>> > > >> > > >>> Again, attachment didn't come thru. > > >> > > >>>> > > >> > > >>>> Is it possible to formulate as google doc ? > > >> > > >>>> > > >> > > >>>> Thanks > > >> > > >>>> > > >> > > >>>> On Mon, Mar 27, 2017 at 6:19 PM, 杨苏立 Yang Su Li< > > >> [email protected]> > > >> > > >>>> wrote: > > >> > > >>>> > > >> > > >>>> Hi, > > >> > > >>>>> > > >> > > >>>>> I am a graduate student working on scheduling on storage > > >> systems, > > >> > > and we > > >> > > >>>>> are interested in how different threads in HBase interact > with > > >> each > > >> > > >>>>> other > > >> > > >>>>> and how it might affect scheduling. > > >> > > >>>>> > > >> > > >>>>> I have written down my understanding on how HBase/HDFS works > > >> based > > >> > on > > >> > > >>>>> its > > >> > > >>>>> current thread architecture (attached). I am wondering if > the > > >> > > developers > > >> > > >>>>> > > >> > > >>>> of > > >> > > >>>> > > >> > > >>>>> HBase could take a look at it and let me know if anything is > > >> > > incorrect > > >> > > >>>>> or > > >> > > >>>>> inaccurate, or if I have missed anything. > > >> > > >>>>> > > >> > > >>>>> Thanks a lot for your help! > > >> > > >>>>> > > >> > > >>>>> On Wed, Mar 22, 2017 at 3:39 PM, 杨苏立 Yang Su Li< > > >> [email protected] > > >> > > > > >> > > >>>>> wrote: > > >> > > >>>>> > > >> > > >>>>> Hi, > > >> > > >>>>>> > > >> > > >>>>>> I am a graduate student working on scheduling on storage > > >> systems, > > >> > > and > > >> > > >>>>>> we > > >> > > >>>>>> are interested in how different threads in HBase interact > > with > > >> > each > > >> > > >>>>>> > > >> > > >>>>> other > > >> > > >>>> > > >> > > >>>>> and how it might affect scheduling. > > >> > > >>>>>> > > >> > > >>>>>> I have written down my understanding on how HBase/HDFS > works > > >> based > > >> > > on > > >> > > >>>>>> > > >> > > >>>>> its > > >> > > >>>> > > >> > > >>>>> current thread architecture (attached). I am wondering if > the > > >> > > >>>>>> > > >> > > >>>>> developers of > > >> > > >>>> > > >> > > >>>>> HBase could take a look at it and let me know if anything is > > >> > > incorrect > > >> > > >>>>>> > > >> > > >>>>> or > > >> > > >>>> > > >> > > >>>>> inaccurate, or if I have missed anything. > > >> > > >>>>>> > > >> > > >>>>>> Thanks a lot for your help! > > >> > > >>>>>> > > >> > > >>>>>> -- > > >> > > >>>>>> Suli Yang > > >> > > >>>>>> > > >> > > >>>>>> Department of Physics > > >> > > >>>>>> University of Wisconsin Madison > > >> > > >>>>>> > > >> > > >>>>>> 4257 Chamberlin Hall > > >> > > >>>>>> Madison WI 53703 > > >> > > >>>>>> > > >> > > >>>>>> > > >> > > >>>>>> > > >> > > >>>>> -- > > >> > > >>>>> Suli Yang > > >> > > >>>>> > > >> > > >>>>> Department of Physics > > >> > > >>>>> University of Wisconsin Madison > > >> > > >>>>> > > >> > > >>>>> 4257 Chamberlin Hall > > >> > > >>>>> Madison WI 53703 > > >> > > >>>>> > > >> > > >>>>> > > >> > > >>>>> > > >> > > >>> > > >> > > >>> > > >> > > >>> > > >> > > > > > >> > > > > > >> > > > -- > > >> > > > Suli Yang > > >> > > > > > >> > > > Department of Physics > > >> > > > University of Wisconsin Madison > > >> > > > > > >> > > > 4257 Chamberlin Hall > > >> > > > Madison WI 53703 > > >> > > > > >> > > > >> > > > >> > > > >> > -- > > >> > Suli Yang > > >> > > > >> > Department of Physics > > >> > University of Wisconsin Madison > > >> > > > >> > 4257 Chamberlin Hall > > >> > Madison WI 53703 > > >> > > > >> > > > > > > > > > > > > -- > > > Suli Yang > > > > > > Department of Physics > > > University of Wisconsin Madison > > > > > > 4257 Chamberlin Hall > > > Madison WI 53703 > > > > > > > > > > > > -- > > Suli Yang > > > > Department of Physics > > University of Wisconsin Madison > > > > 4257 Chamberlin Hall > > Madison WI 53703 > > > -- Suli Yang Department of Physics University of Wisconsin Madison 4257 Chamberlin Hall Madison WI 53703
