Hi Chao, I just injected -EIO for one page among two pages in total into database file. Then, I tested valid and invalid journal file to see how sqlite recovers the transaction.
Interestingly, if journal is valid, database file is recovered, as I could see the transaction result even after it shows EIO. But, in the invalid journal case, somehow it drops database changes. I'm not sure it was because I just skip second page write of database file tho. (I added random bytes into journal pages.) I'll break the database file with more random bytes likewise what I did for journal. Thanks, On Fri, Jan 08, 2016 at 11:43:06AM -0800, Jaegeuk Kim wrote: > On Fri, Jan 08, 2016 at 08:05:52PM +0800, Chao Yu wrote: > > Hi Jaegeuk, > > > > Any progress on this patch? > > Swamped. Will do. > > Thanks, > > > > > Thanks, > > > > > -----Original Message----- > > > From: Chao Yu [mailto:c...@kernel.org] > > > Sent: Friday, January 01, 2016 8:14 PM > > > To: Jaegeuk Kim > > > Cc: linux-ker...@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net > > > Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: support revoking atomic written > > > pages > > > > > > Hi Jaegeuk, > > > > > > On 1/1/16 11:50 AM, Jaegeuk Kim wrote: > > > > Hi Chao, > > > > > > > > ... > > > > > > > >>>>> On Tue, Dec 29, 2015 at 11:12:36AM +0800, Chao Yu wrote: > > > >>>>>> f2fs support atomic write with following semantics: > > > >>>>>> 1. open db file > > > >>>>>> 2. ioctl start atomic write > > > >>>>>> 3. (write db file) * n > > > >>>>>> 4. ioctl commit atomic write > > > >>>>>> 5. close db file > > > >>>>>> > > > >>>>>> With this flow we can avoid file becoming corrupted when abnormal > > > >>>>>> power > > > >>>>>> cut, because we hold data of transaction in referenced pages > > > >>>>>> linked in > > > >>>>>> inmem_pages list of inode, but without setting them dirty, so > > > >>>>>> these data > > > >>>>>> won't be persisted unless we commit them in step 4. > > > >>>>>> > > > >>>>>> But we should still hold journal db file in memory by using > > > >>>>>> volatile write, > > > >>>>>> because our semantics of 'atomic write support' is not full, in > > > >>>>>> step 4, we > > > >>>>>> could be fail to submit all dirty data of transaction, once > > > >>>>>> partial dirty > > > >>>>>> data was committed in storage, db file should be corrupted, in > > > >>>>>> this case, > > > >>>>>> we should use journal db to recover the original data in db file. > > > >>>>> > > > >>>>> Originally, IOC_ABORT_VOLATILE_WRITE was supposed to handle commit > > > >>>>> failures, > > > >>>>> since database should get its error literally. > > > >>>>> > > > >>>>> So, the only thing that we need to do is keeping journal data for > > > >>>>> further db > > > >>>>> recovery. > > > >>>> > > > >>>> IMO, if we really support *atomic* interface, we don't need any > > > >>>> journal data > > > >>>> kept by user, because f2fs already have it in its storage since we > > > >>>> always > > > >>>> trigger OPU for pages written in atomic-write opened file, f2fs can > > > >>>> easily try > > > >>>> to revoke (replace old to new in metadata) when any failure exist in > > > >>>> atomic > > > >>>> write process. > > > >>> > > > >>> Yeah, so current design does not fully support atomic writes. IOWs, > > > >>> volatile > > > >>> writes for journal files should be used together to minimize sqlite > > > >>> change as > > > >>> much as possible. > > > >>> > > > >>>> But in current design, we still hold journal data in memory for > > > >>>> recovering for > > > >>>> *rare* failure case. I think there are several issues: > > > >>>> a) most of time, we are in concurrent scenario, so if large number > > > >>>> of journal > > > >>>> db files were opened simultaneously, we are under big memory > > > >>>> pressure. > > > >>> > > > >>> In current android, I've seen that this is not a big concern. Even > > > >>> there is > > > >>> memory pressure, f2fs flushes volatile pages. > > > >> > > > >> When I change to redirty all volatile pages in ->writepage, android > > > >> seems go > > > >> into an infinite loop when doing recovery flow of f2fs data partition > > > >> in startup. > > > >> > > > >> if (f2fs_is_volatile_file(inode)) > > > >> goto redirty_out; > > > > > > > > Where did you put this? It doesn't flush at all? Why? > > > > > > Original place in ->writepage, just remove two other conditions. > > > > > > To avoid potential random writebacking of dirty page in journal which > > > cause unpredicted corrupting in journal. > > > > > > > Practically, the peak amount of journal writes depend on how many > > > > transactions > > > > are processing concurrently. > > > > I mean, in-memory pages are dropped at the end of every transaction. > > > > You can check the number of pages through f2fs_stat on your phone. > > > > > > > >> I didn't dig details, but I think there may be a little risk for this > > > >> design. > > > >> > > > >>> > > > >>>> b) If we are out of memory, reclaimer tries to write page of journal > > > >>>> db into > > > >>>> disk, it will destroy db file. > > > >>> > > > >>> I don't understand. Could you elaborate why journal writes can > > > >>> corrupt db? > > > >> > > > >> Normally, we keep pages of journal in memory, but partial page in > > > >> journal > > > >> will be write out to device by reclaimer when out of memory. So this > > > >> journal > > > >> may have valid data in its log head, but with corrupted data, then > > > >> after > > > >> abnormal powe-cut, recovery with this journal before a transaction will > > > >> destroy db. Right? > > > > > > > > Just think about sqlite without this feature. > > > > Broken journal is pretty normal case for sqlite. > > > > > > Maybe, if it is caused by bug or design issue of software, no matter db > > > system > > > or filesystem, we should try our best to fix it to avoid generating > > > broken journals. > > > > > > > > > > >>> > > > >>>> c) Though, we have journal db file, we will face failure of > > > >>>> recovering db file > > > >>>> from journal db due to ENOMEM or EIO, then db file will be corrupted. > > > >>> > > > >>> Do you mean the failure of recovering db with a complete journal? > > > >>> Why do we have to handle that? That's a database stuff, IMO. > > > >> > > > >> Yes, just list for indicating we will face the same issue which is > > > >> hard to > > > >> handle both in original design and new design, so the inner revoking > > > >> failure > > > >> issue would not be a weak point or flaw of new design. > > > >> > > > >>> > > > >>>> d) Recovery flow will make data page dirty, triggering both data > > > >>>> stream and > > > >>>> metadata stream, there should be more IOs than in inner revoking in > > > >>>> atomic-interface. > > > >>> > > > >>> Well, do you mean there is no need to recover db after revoking? > > > >> > > > >> Yes, revoking make the same effect like the recovery of sqlite, so > > > >> after > > > >> revoking, recovery is no need. > > > > > > > > Logically, it doesn't make sense. If there is a valid journal file, it > > > > should > > > > redo the previous transaction. No? > > > > > > As we know, in sqlite, before we commit a transaction, we will use > > > journal to > > > record original data of pages which will be updated in following > > > transaction, so > > > in following if a) abnormal power-cut, b) commit error, c) redo command > > > was > > > triggered by user, we will recover db with journal. > > > > > > Ideally, if we support atomic write interface, in there should always > > > return two > > > status in atomic write interface: success or fail. If success, > > > transaction was > > > committed, otherwise, it looks like nothing happened, user will be told > > > transaction was failed. Then, journals in sqlite could no longer be used, > > > eventually no journal, no recovery. > > > > > > The only thing we should concern is inner failure (e.g. ENOMEM, ENOSPC) of > > > revoking in commit interface since it could destroy db file permanently > > > w/o > > > journal. IMO, some optimization could be done for these cases: > > > 1. ENOMEM: enable retrying or mark accessed flag in page in advance. > > > 2. ENOSPC: preallocate blocks for node blocks and data blocks. > > > > > > These optimizations couldn't guarantee no failure in revoking operation > > > completely, luckily, those are not common cases, and they also happen in > > > sqlite > > > w/o atomic feature. > > > > > > One more possible proposal is: if we support reflink feature like > > > ocfs2/xfs, I > > > guess we can optimize DB like: > > > 1. reflink db to db.ref > > > 2. do transaction in db.ref > > > - failed, rm db.ref > > > - power-cut rm db.ref > > > 3. rename db.ref to db > > > > > > > > > > >> One more case is that user can send a command to abort current > > > >> transaction, > > > >> it should be happened before atomic_commit operation, which could > > > >> easily > > > >> handle with abort_commit ioctl. > > > >> > > > >>> > > > >>>> e) Moreover, there should be a hole between 1) commit fail and 2) > > > >>>> abort write & > > > >>>> recover, checkpoint will persist the corrupt data in db file, > > > >>>> following abnormal > > > >>>> power-cut will leave that data in disk. > > > >>> > > > >>> Yes, in that case, database should recover corrupted db with its > > > >>> journal file. > > > >> > > > >> Journal could be corrupted as I descripted in b). > > > > > > > > Okay, so what I'm thinking is like this. > > > > It seems there are two corruption cases after journal writes. > > > > > > > > 1. power cut during atomic writes > > > > - broken journal file and clean db file -> give up > > > > - luckily, valid journal file and clean db file -> recover db > > > > > > > > 2. error during atomic writes > > > > a. power-cut before abort completion > > > > - broken journal file and broken db file -> revoking is needed! > > > > > > > > b. after abort > > > > - valid journal file and broken db file -> recover db (likewise plain > > > > sqlite) > > > > > > > > Indeed, in the 2.a. case, we need revoking; I guess that's what you > > > > mentioned. > > > > But, I think, even if revoking is done, we should notify an error to > > > > abort and > > > > recover db by 2.b. > > > > > > > > Something like this after successful revoking. > > > > > > > > 1. power cut during atomic writes > > > > - broken journal file and clean db file -> give up > > > > - luckily, valid journal file and clean db file -> recover db > > > > > > > > 2. error during atomic writes w/ revoking > > > > a. power-cut before abort completion > > > > - broken journal file and clean db file -> give up > > > > - luckily, valid journal file and clean db file -> recover db > > > > > > > > b. after abort > > > > - valid journal file and clean db file -> recover db > > > > > > That's right. > > > > > > > > > > > Let me verify these scenarios first. :) > > > > > > OK. :) > > > > > > Thanks, > > > > > > > > > > > Thanks, > > > > > > > >>> > > > >>>> With revoking supported design, we can not solve all above issues, > > > >>>> we will still > > > >>>> face the same issue like c), but it will be a big improve if we can > > > >>>> apply this > > > >>>> in our interface, since it provide a way to fix the issue a) b) d). > > > >>>> And also for > > > >>>> e) case, we try to rescue data in first time that our revoking > > > >>>> operation would be > > > >>>> protected by f2fs_lock_op to avoid checkpoint + power-cut. > > > >>>> > > > >>>> If you don't want to have a big change in this interface or recovery > > > >>>> flow, how > > > >>>> about keep them both, and add a mount option to control inner > > > >>>> recovery flow? > > > >>> > > > >>> Hmm, okay. I believe the current design is fine for sqlite in android. > > > >> > > > >> I believe new design will enhance in memory usage and error handling > > > >> of sqlite > > > >> in android, and hope this can be applied. But, I can understand that > > > >> if you > > > >> were considerring about risk control and backward compatibility, since > > > >> this > > > >> change affects all atomic related ioctls. > > > >> > > > >>> For other databases, I can understand that they can use atomic_write > > > >>> without > > > >>> journal control, which is a sort of stand-alone atomic_write. > > > >>> > > > >>> It'd better to add a new ioctl for that, but before adding it, can we > > > >>> find > > > >>> any usecase for this feature? (e.g., postgresql, mysql, mariadb, > > > >>> couchdb?) > > > >> > > > >> You mean investigating or we can only start when there is a clear > > > >> commercial > > > >> demand ? > > > >> > > > >>> Then, I expect that we can define a more appropriate and powerful > > > >>> ioctl. > > > >> > > > >> Agreed :) > > > >> > > > >> Thanks, > > > >> > > > >>> > > > >>> Thanks, > > > >>> > > > >>>> > > > >>>> How do you think? :) > > > >>>> > > > >>>> Thanks, > > > >>>> > > > >>>>> But, unfortunately, it seems that something is missing in the > > > >>>>> current implementation. > > > >>>>> > > > >>>>> So simply how about this? > > > >>>>> > > > >>>>> A possible flow would be: > > > >>>>> 1. write journal data to volatile space > > > >>>>> 2. write db data to atomic space > > > >>>>> 3. in the error case, call ioc_abort_volatile_writes for both > > > >>>>> journal and db > > > >>>>> - flush/fsync journal data to disk > > > >>>>> - drop atomic data, and will be recovered by database with journal > > > >>>>> > > > >>>>> From cb33fc8bc30981c370ec70fe68871130109793ec Mon Sep 17 00:00:00 > > > >>>>> 2001 > > > >>>>> From: Jaegeuk Kim <jaeg...@kernel.org> > > > >>>>> Date: Tue, 29 Dec 2015 15:46:33 -0800 > > > >>>>> Subject: [PATCH] f2fs: fix f2fs_ioc_abort_volatile_write > > > >>>>> > > > >>>>> There are two rules to handle aborting volatile or atomic writes. > > > >>>>> > > > >>>>> 1. drop atomic writes > > > >>>>> - we don't need to keep any stale db data. > > > >>>>> > > > >>>>> 2. write journal data > > > >>>>> - we should keep the journal data with fsync for db recovery. > > > >>>>> > > > >>>>> Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org> > > > >>>>> --- > > > >>>>> fs/f2fs/file.c | 13 ++++++++++--- > > > >>>>> 1 file changed, 10 insertions(+), 3 deletions(-) > > > >>>>> > > > >>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c > > > >>>>> index 91f576a..d16438a 100644 > > > >>>>> --- a/fs/f2fs/file.c > > > >>>>> +++ b/fs/f2fs/file.c > > > >>>>> @@ -1433,9 +1433,16 @@ static int > > > >>>>> f2fs_ioc_abort_volatile_write(struct file *filp) > > > >>>>> if (ret) > > > >>>>> return ret; > > > >>>>> > > > >>>>> - clear_inode_flag(F2FS_I(inode), FI_ATOMIC_FILE); > > > >>>>> - clear_inode_flag(F2FS_I(inode), FI_VOLATILE_FILE); > > > >>>>> - commit_inmem_pages(inode, true); > > > >>>>> + if (f2fs_is_atomic_file(inode)) { > > > >>>>> + clear_inode_flag(F2FS_I(inode), FI_ATOMIC_FILE); > > > >>>>> + commit_inmem_pages(inode, true); > > > >>>>> + } > > > >>>>> + if (f2fs_is_volatile_file(inode)) { > > > >>>>> + clear_inode_flag(F2FS_I(inode), FI_VOLATILE_FILE); > > > >>>>> + ret = commit_inmem_pages(inode, false); > > > >>>>> + if (!ret) > > > >>>>> + ret = f2fs_sync_file(filp, 0, LLONG_MAX, 0); > > > >>>>> + } > > > >>>>> > > > >>>>> mnt_drop_write_file(filp); > > > >>>>> return ret; > > > >>>>> -- > > > >>>>> 2.6.3 > > > >>>> > > > > > > > > ------------------------------------------------------------------------------ > > > > _______________________________________________ > > > > Linux-f2fs-devel mailing list > > > > Linux-f2fs-devel@lists.sourceforge.net > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > > > > > > > > > ------------------------------------------------------------------------------ > > > _______________________________________________ > > > Linux-f2fs-devel mailing list > > > Linux-f2fs-devel@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > ------------------------------------------------------------------------------ > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. 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