Hi Denis, the short answer here, Apache Ignite guarantees ACID, and for D-Durability it is required to save all changes in some WAL/Redo Log to have a safe way to recover from any hardware failures/disk outage.
Should the user disable WAL, he/she could potentially lose durability. Sincerely, Dmitriy Pavlov вт, 10 нояб. 2020 г. в 09:57, ткаленко кирилл <tkalkir...@yandex.ru>: > Hello guys again! > > Does anyone know why we are doing any calculation here > IgniteUtils#adjustedWalHistorySize at all? > Would it be easier to always take the > DataStorageConfiguration#maxWalArchiveSize? It seems that the user can > easily do this himself by changing the value by 1 byte. > > 06.11.2020, 13:56, "Ivan Daschinsky" <ivanda...@gmail.com>: > > Alex, thanks for pointing that out. Shame that I missed it. > > > > пт, 6 нояб. 2020 г. в 13:45, Alex Plehanov <plehanov.a...@gmail.com>: > > > >> Guys, > >> > >> We already have FileWriteAheadLogManager#maxSegCountWithoutCheckpoint. > >> Checkpoint triggered if there are too many WAL segments without > checkpoint. > >> Looks like you are talking about this feature. > >> > >> пт, 6 нояб. 2020 г. в 13:21, Ivan Daschinsky <ivanda...@gmail.com>: > >> > >> > Kirill and I discussed privately proposed approach. As far as I > >> understand, > >> > Kirill suggests to implement some > >> > heuristic to do a force checkpoint in some cases if user by mistake > >> > misconfigured cluster in order to preserve > >> > requested size of WAL archive. > >> > Currently, as for me, this approach is questionable, because it can > cause > >> > some performance problems. But as an option, > >> > it can be used and should be switchable. > >> > > >> > пт, 6 нояб. 2020 г. в 12:36, Ivan Daschinsky <ivanda...@gmail.com>: > >> > > >> > > Kirill, how your approach will help if user tuned a cluster to do > >> > > checkpoints rarely under load? > >> > > No way. > >> > > > >> > > пт, 6 нояб. 2020 г. в 12:19, ткаленко кирилл <tkalkir...@yandex.ru > >: > >> > > > >> > >> Ivan, I agree with you that the archive is primarily about > >> optimization. > >> > >> > >> > >> If the size of the archive is critical for the user, we have no > >> > >> protection against this, we can always go beyond this limit. > >> > >> Thus, the user needs to remember this and configure it in some > way. > >> > >> > >> > >> I suggest not to exceed this limit and give the expected behavior > for > >> > the > >> > >> user. At the same time, the segments needed for recovery will > remain > >> and > >> > >> there will be no data loss. > >> > >> > >> > >> 06.11.2020, 11:29, "Ivan Daschinsky" <ivanda...@gmail.com>: > >> > >> > Guys, fisrt of all, archiving is not for PITR at all, this is > >> > >> optimization. > >> > >> > If we disable archiving, every rollover we need to create new > file. > >> If > >> > >> we > >> > >> > enable archiving, we reserve 10 (by default) segments filled > with > >> > >> zeroes. > >> > >> > We use mmap by default, so if we use no-archiver approach: > >> > >> > 1. We firstly create new empty file > >> > >> > 2. Call on it sun.nio.ch.FileChannelImpl#map, thats under the > hood > >> > >> > a. If file is shorter, than wal segment size, it > >> > >> > calls sun.nio.ch.FileDispatcherImpl#truncate0, this is under the > >> hood > >> > >> just > >> > >> > a system call truncate [1] > >> > >> > b. Than it calls system call mmap on this > >> > >> > file sun.nio.ch.FileChannelImpl#map0, under the hood see [2] > >> > >> > These manipulation are not free and cheap. So rollover will be > much > >> > much > >> > >> > slower. > >> > >> > If archiving is enabled, 10 segments are already preallocated > at the > >> > >> moment > >> > >> > of node's start. > >> > >> > > >> > >> > When archiving is enabled, archiver just copy previous > preallocated > >> > >> segment > >> > >> > and move it to archive directory. > >> > >> > This archived segment is crucial for recovery. When new > checkpoints > >> > >> > finished, all eligible for trunocating segments are just > removed. > >> > >> > > >> > >> > If archiving is disabled, we also write WAL segments in wal > >> directory > >> > >> and > >> > >> > disabling archiving don't prevent you from storing segments, if > they > >> > are > >> > >> > required for recovery. > >> > >> > > >> > >> >>> Before increasing the size of WAL archive (transferring to > archive > >> > >> > > >> > >> > /rollOver, compression, decompression), we can make sure that > there > >> > >> will be > >> > >> > enough space in the archive and if there is no such, then we > will > >> try > >> > to > >> > >> >>> clean it. We cannot delete those segments that are required > for > >> > >> recovery > >> > >> > > >> > >> > (between the last two checkpoints) and reserved for example for > >> > >> historical > >> > >> > rebalancing. > >> > >> > First of all, compression/decompression is offtopic here. > >> > >> > Secondly, wal segments are required only with idx higher than > LAST > >> > >> > checkpoint marker. > >> > >> > Thirdly, archiving and rolling over can be during checkpoint > and we > >> > can > >> > >> > broke everything accidentially. > >> > >> > Fourthly, I see no benefits to overcomplicated already > complicated > >> > >> logic. > >> > >> > This is basically problem of misunderstanding and tuning. > >> > >> > There are a lot of similar topics for almost every DB. [3] > >> > >> > > >> > >> > [1] -- https://man7.org/linux/man-pages/man2/ftruncate.2.html > >> > >> > [2] -- https://man7.org/linux/man-pages/man2/mmap.2.html > >> > >> > [3] -- > >> > >> > > >> > >> > >> > > >> > https://www.google.com/search?q=pg_wal%2Fxlogtemp+no+space+left+on+device&oq=pg+wal+no > >> > >> > > >> > >> > пт, 6 нояб. 2020 г. в 10:42, ткаленко кирилл < > tkalkir...@yandex.ru > >> >: > >> > >> > > >> > >> >> Hi, Ivan! > >> > >> >> > >> > >> >> I have only described ideas. But here are a few more details. > >> > >> >> > >> > >> >> We can take care not to go beyond > >> > >> >> DataStorageConfiguration#maxWalArchiveSize. > >> > >> >> > >> > >> >> Before increasing the size of WAL archive (transferring to > archive > >> > >> >> /rollOver, compression, decompression), we can make sure that > >> there > >> > >> will be > >> > >> >> enough space in the archive and if there is no such, then we > will > >> > try > >> > >> to > >> > >> >> clean it. We cannot delete those segments that are required for > >> > >> recovery > >> > >> >> (between the last two checkpoints) and reserved for example for > >> > >> historical > >> > >> >> rebalancing. > >> > >> >> > >> > >> >> We can receive a notification about the change of checkpoints > and > >> > the > >> > >> >> reservation / release of segments, thus we can know how many > >> > segments > >> > >> we > >> > >> >> can delete right now. > >> > >> >> > >> > >> >> 06.11.2020, 09:53, "Ivan Daschinsky" <ivanda...@gmail.com>: > >> > >> >> >>> For example, when trying to move a segment to the archive. > >> > >> >> > > >> > >> >> > We cannot do this, we will lost data. We can truncate > archived > >> > >> segment if > >> > >> >> > and only if it is not required for recovery. If last > checkpoint > >> > >> marker > >> > >> >> > points to segment > >> > >> >> > with lower index, we cannot delete any segment with higher > >> index. > >> > >> So the > >> > >> >> > only moment where we can remove truncate segments is a > finish of > >> > >> >> checkpoint. > >> > >> >> > > >> > >> >> > пт, 6 нояб. 2020 г. в 09:46, ткаленко кирилл < > >> > tkalkir...@yandex.ru > >> > >> >: > >> > >> >> > > >> > >> >> >> Hello, everybody! > >> > >> >> >> > >> > >> >> >> As far as I know, WAL archive is used for PITP(GridGain > >> feature) > >> > >> and > >> > >> >> >> historical rebalancing. > >> > >> >> >> > >> > >> >> >> Facundo seems to have a problem with running out of > directory > >> > >> >> >> (/opt/work/walarchive) space. > >> > >> >> >> Currently, WAL archive is cleared at the end of checkpoint. > >> > >> Potentially > >> > >> >> >> long transaction may prevent checkpoint starting, thereby > not > >> > >> cleaning > >> > >> >> WAL > >> > >> >> >> archive, which will lead to such an error. > >> > >> >> >> At the moment, I see such a WA to increase size of directory > >> > >> >> >> (/opt/work/walarchive) in k8s and avoid long transactions or > >> > >> something > >> > >> >> like > >> > >> >> >> that that modifies data and runs for a long time. > >> > >> >> >> > >> > >> >> >> And it is best to fix the logic of working with WAL > archive. I > >> > >> think we > >> > >> >> >> should remove WAL archive cleanup from the end of the > >> checkpoint > >> > >> and > >> > >> >> do it > >> > >> >> >> on demand. For example, when trying to move a segment to the > >> > >> archive. > >> > >> >> >> > >> > >> >> >> 06.11.2020, 01:58, "Denis Magda" <dma...@apache.org>: > >> > >> >> >> > Folks, > >> > >> >> >> > > >> > >> >> >> > In my understanding, you need the archives only for > features > >> > >> such as > >> > >> >> >> PITR. > >> > >> >> >> > Considering, that the PITR functionality is not provided > in > >> > >> Ignite > >> > >> >> why do > >> > >> >> >> > we have the archives enabled by default? > >> > >> >> >> > > >> > >> >> >> > How about having this feature disabled by default to > prevent > >> > the > >> > >> >> >> following > >> > >> >> >> > issues experienced by our users: > >> > >> >> >> > > >> > >> >> >> > >> > >> >> > >> > >> > >> > > >> > http://apache-ignite-users.70518.x6.nabble.com/WAL-and-WAL-Archive-volume-size-recommendation-td34458.html > >> > >> >> >> > > >> > >> >> >> > - > >> > >> >> >> > Denis > >> > >> >> > > >> > >> >> > -- > >> > >> >> > Sincerely yours, Ivan Daschinskiy > >> > >> > > >> > >> > -- > >> > >> > Sincerely yours, Ivan Daschinskiy > >> > >> > >> > > > >> > > > >> > > -- > >> > > Sincerely yours, Ivan Daschinskiy > >> > > > >> > > >> > > >> > -- > >> > Sincerely yours, Ivan Daschinskiy > >> > > > > > -- > > Sincerely yours, Ivan Daschinskiy >
