Jialin, I'm curious to know why you're asking all these questions. Are you working on some research project that involves BookKeeper? Otherwise, what's your use case if you don't mind sharing?
-Flavio On Monday, July 21, 2014 1:34 PM, Ivan Kelly <[email protected]> wrote: > > >We have considered something like this in the past. However, it would >mean that reads will affect the latency or writes, as they will move >the disk head. > >It's also the case that the interleaved entrylog performs really badly >on reads. Work has been done recently to improve this, by buffering >entries and sorting them by ledger id before flushing to the >entrylog. This means that reads for a specific ledger will be >sequential as opposed to jumping all over the place as it has to do >now. If we used the journal for this, then we wouldn't be able to do >this processing, as the point of the journal is to ensure that the >entry is on persistent storage before replying to the client. If we >buffered enough to get benefit from sorting, write latency would be >enormous. > >-Ivan > > >On Sat, Jul 19, 2014 at 01:55:16PM -0700, Jaln wrote: >> Thank you so much, Rakesh, >> Without consideration of performance, can we just maintain one file. For >> example journal file, and the index for each entry. >> >> Best, >> Jaln >> >> >> On Fri, Jul 18, 2014 at 11:23 PM, Rakesh Radhakrishnan < >> [email protected]> wrote: >> >> > Hi Jaln, >> > >> > >>>>>>for the data in the journal file(*.txn) and the entry log >> > file(*.log), are >> > >>>>>>they similar? >> > >>>>>>for example, when I add an entry, this opeartion and the entry data >> > will be >> > >>>>>>logged in the journal file, >> > >>>>>>and the entry data will be logged in the entry log file (*.log), >> > right? >> > >> > As I mentioned earlier, when an entry is added Bookie server will add only >> > this entry to the journal file and will send a response back to the >> > client after the successful flush to the disk. Later during checkpointing >> > time, server will read the journal entries and add it to the entry logger >> > files. Also, it will generate index files corresponding to each ledgers for >> > the faster access. This old journal file will be garbage collected, because >> > all these entries are mapped it to the entry logger. >> > >> > >>>>>what's the purpose of the two files? >> > AFAIK, adding to entry log and generating index is a costly I/O operation >> > and will affect the performance. Thats the reason, first will only add >> > transactions to journal file and send a response quickly. Later will add it >> > to the entrylog file & index files offline. >> > >> > Total bookie stored data = entry logger data + journal data(most recent >> > data) >> > >> > *For example:* I'm calling write operation as transaction. Assume client >> > has performed 20 transactions. All these exists only in the journal file. >> > Say, now checkpointing triggered. It will add these 20 transactions to the >> > entry logger file and generate indexes. Again assume user performed 10 more >> > transactions. Now we have total 30 transactions. >> > >> > Bookie data(30 transactions) = 20 + 10. >> > >> > Regards, >> > Rakesh >> > >> > >> > >> > On Sat, Jul 19, 2014 at 9:52 AM, Jaln <[email protected]> wrote: >> > >> > > Thanks Rakesh, >> > > for the data in the journal file(*.txn) and the entry log file(*.log), >> > are >> > > they similar? >> > > for example, when I add an entry, this opeartion and the entry data will >> > be >> > > logged in the journal file, >> > > and the entry data will be logged in the entry log file (*.log), right? >> > > what's the purpose of the two files? >> > > >> > > Thanks, >> > > Jaln >> > > >> > > On Fri, Jul 18, 2014 at 8:16 PM, Rakesh Radhakrishnan < >> > > [email protected]> wrote: >> > > >> > > > Hi Jaln, >> > > > >> > > > No, both are different. I hope you are asking about 'entry log' files >> > and >> > > > 'journal' files >> > > > >> > > > *Journal : *When client performs a write operation (such as adding an >> > > entry >> > > > etc), it is first recorded in the journal file. Journal will be flushed >> > > and >> > > > synced after every write operation before a success code is returned to >> > > the >> > > > client. This ensures that no operation is lost due to machine failure. >> > > > >> > > > *Entry Log : *It is not updated for every write operation, bookie >> > server >> > > > will do it lazily. Because writing out the ledger involves - update >> > > ledger >> > > > index files to faster look up and add entry to the logger file. This >> > will >> > > > be a costly operation and will affect the performance. >> > > > >> > > > In Bookie, there is a dedicated thread to play journal transactions and >> > > add >> > > > it to the logger lazily, this is called as checkpointing operation. >> > This >> > > > will be performed periodically, now the data will be persisted to >> > ledger >> > > > index files and entry logger. By default the 'flushInterval' is 100 >> > > > milliseconds. Probably you can configure a bigger value to see the >> > > > difference. >> > > > >> > > > *"SyncThread"* is a background thread which help checkpointing. After a >> > > > ledger storage is checkpointed, the journal files added before >> > checkpoint >> > > > will be garbage collected. >> > > > >> > > > Cheers, >> > > > Rakesh >> > > > >> > > > >> > > > On Sat, Jul 19, 2014 at 1:41 AM, Jaln <[email protected]> wrote: >> > > > >> > > > > Hi, >> > > > > is the ledger file and journal file same? >> > > > > I run the bookkeeper and generate the bookie, >> > > > > inside the bookie, I found the journal file and ledger file are >> > almost >> > > > > same. >> > > > > >> > > > > Best, >> > > > > Jialin >> > > > > >> > > > >> > > >> > > > >
