1 in 128 chance of a failure on a given power-up. Python's wrapper is one of the worst. Sometimes (eg databases), the backup program is able to run application specific logic that works in with this (eg flush all database buffers before the snapshot). I'd also wonder about how old this part is and whether it's partially based on Windows. Doesn't mean you can't add more to that buffer or have to wait. When is it safe to copy a SQLite data file that is currently open? I get an error when trying to change the filename to '' after setting all to inactive: To close a dataset call Close or Active := False. The "one connection per operation" approach is NOT ideal for SQLite because there is an actual database file that needs a handle created/closed each time. In case the answer is b) then it seems to me, though I may be overlooking something, that we could allow calls like b) and inside of the dup2 syscall keep the id of the fd that we are using as newfd, since it is unambiguously requested that this is intended, while at the same never reusing fd id in the dup syscall. https://mitpress.mit.edu/books/fun-and-profit. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. That said, this is rather unlikely to happen in practice. It's trivial to copy a SQLite database but it's less trivial to do this in a way that won't corrupt it. A "supposedly" read-only connection can end up doing writes for example, consolidating WAL log into the main DB file. I want to backup the whole database (it's all in one file) I have attached a zip file that shows the problem. Even in WAL mode, you can still get a SQLITE_BUSY error even when just trying to open a new connection. People who know what NFS is will be on Emby or similar before I finish writing this comment. One can easily see this by committing a large transaction to an SQLite database on a USB memory stick. program crash, an operating system crash, or a power failure to the You just do the best that you can. If you are using WAL, I feel volume-level snapshots are an acceptable approach. debiting one account and crediting another). > Backup or restore while a transaction is active. Can they be applied to other DBMSs? Very interesting read! @coleifer (author of peewee) has a pretty informative blog post exploring in part transactional semantics, which might be of value to people who want to know more about this. How APIs can take the pain out of legacy system headaches (Ep. In another life (2007) I worked for a company that does digital signage. That can cause SQLITE_BUSY errors. I wonder how much this cost the company to fully resolve. ), make my code more complicated (I'd basically need to automate common dba work), and Windows support is shaky (last time I checked, at least). 1. This seems to mean that if a regular end user is browsing the web while backups run on their computer, it's possible they could be unlucky and get a bad backup that would corrupt the database if they had to restore it. Windows backup for example uses VSS (Volume Shadow Copies [1])) which should not suffer from this problem. Trying to figure out what was causing this we realized our pc manufacturer was using the same sku but hardware inside could vary and in particular the hard drive. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. That's how people did redirection of stderr before threads and before dup2. But it would be interesting to find out how many wide-spread pieces of open source code do it that way, and for all code that does one could submit patches to change them to using the explicit dup2. There are several ways of backing up a SQLite database to file. This lags and isn't a great option for live databases and if you're accessing the same SQLite db outside the container and inside, you will see corruption happen. Both Windows and macOS make it pretty easy to set these up with an external hard drive. My Materialistic app crashed about 30 seconds prior to opening this thread. The software on them relied heavily on SQLite. in the end they had to suck it up and put in a server class drive (something with a high duty cycle rating). A decade ago the behavior of most file systems was quite poor in the face of underlying hardware failures but a lot of work has gone into improving the situation. > Programs can deal with the issue by performing atomic full writes by performing renames, but most programs don't bother to. I spent several years working for a major HDD manufacturer and their firmware QA process included a test rig which would repeatedly pull power to the drive while sending write and flush commands. So it seems by tracking wall time, the library could do better than have to rely on the drive, and could be more on guard against lying drives. I only have datasets and datasources to close and with all the datasets set to 'active'=false, I still can't copy this file. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers. Also mrmikehicks, thank you, I had been looking for a way to backup sqlite3 db's, so you have helped me as well. If you have to handle (write code for) 2 and 3, why isnt something like Postgres better? Also very likely a particular model of the drive and also sheer luck that one worked and one did not. Our manager had to fight with the sales rep for about a month before they relented. Snapshots are global "freeze" of file system, which is consistent because of ACID. I am trying to just copy the sqlite3 .db file for backup. I'll try to build the APK myself when I get some spare time. E.g. If you use a mounted volume in Win/Mac it does a syncing, not a direct mount/share. Is there a faction in the Ukrainian parliament favoring an immediate ceasefire? Of course fsync() sends a flush to the disk (unless you use non-standard mount options or "eatmydata"). I tried to add a backup function, and found that I can't copy the actual sqlite3 database file (in my case research.db) Every attempt to copy this file within the application as a backup fails to open the file. https://pubs.opengroup.org/onlinepubs/9699919799/functions/s > On program startup, the integer file descriptors associated with the streams stdin, stdout, and stderr are 0, 1, and 2, respectively. One could make an unprincipled exception for them, of course. A vacuum phase would still have to do an atomic rename. Didn't see your reply before commenting, but it gave me a thought: We really only need a "local" solution. Fixing problems on one bespoke system is a lot easier than fixing the same problem 8000 times, and of course with a large sample size the number of problems experienced goes up. If the file exists, it will open it. I'm assuming it was: Disk drives that do not honor sync requests. Maybe those were firmware bugs, maybe they stopped doing it, but it is not something made up. If you dont see any errors after executing that command, this means that the backup is created successfully. If you take a consistent snapshot of the filesystem first, I would think that would be the same as a crash in the middle of a transaction. I have set all 8 or so datasets to inactive, set all datasource components to not enabled. https://devblogs.microsoft.com/oldnewthing/20170510-00/?p=95 https://github.com/dashawn888/sqlite3worker, https://en.wikipedia.org/wiki/Shadow_Copy, http://man7.org/linux/man-pages/man3/stdin.3.html. > The following symbolic values in define the file descriptors that shall be associated with the C-language stdin, stdout, and stderr when the application is started: > STDIN_FILENO Standard input value, stdin. computer. You can also backup a database simply by copying/pasting the physical file on the filesystem. This makes the disk drives seem to operate faster (which is vitally important to the manufacturer so that they can show good benchmark numbers in trade magazines). BIOS would show the disk drive was present but that it had no capacity or name. > I have found that corruption of SQLite files in practice is a very difficult thing to achieve. Write flushing problems would be exacerbated in that environment. I am using sqlite3 datasets, and all is so far working again. And/or options known to cause corruption for this Plex DB usage pattern. An append-only format should work fine with most backup software that copies files. Of course the filesystem usually does, and the physical device itself does, but in the scenario where the OS somehow delivered corrupted data would SQLite at a minimum detect it? I have no issues with this guys client and have been using the free version for 3+ years. You simply stop thinking about databases after a while because everything just works. System would get slower and slower until one day it would hard reboot itself and then claim there was no disk drive installed. Hmm, I checked that one out and it is indeed pretty nice but I don't think I can log in to my account with it. It's a good question. Contrary to popular belief, even consumer drives will honor flush commands. Sqlite is more like a structured persistent file format with a SQL interface than a database. Can you give an example? Is the fact that ZFC implies that 1+1=2 an absolute truth? What you need is the SQLite library which is less than 500KB size. More generally there's typically a much better isolation between database and process on traditional processes which makes it difficult for a misbehaving program to mess directly with the DB. Operating systems lie about local volumes. No idea how many may be failing silently. If you omit the database alias, it will use the main database. dup2() makes newfd be the copy of oldfd, closing newfd first if necessary, but note the following: []. Is open() on something other than /dev/stderr returning 2 a thing? Making statements based on opinion; back them up with references or personal experience. Then you pronounce it sequel. Of course it is. More generally, the question is, does any wide-spread piece of code manually close an fd and then call the dup syscall, and expect the fd id to be exactly the same as the one they themselves closed, instead of using dup2? It would be nice if file descriptors on 64-bit platforms used tagging so the full value could never be reused. The application modifies the database at well-defined points. There are no privileges required to create the databases. How to explain mathematically 2.4 GHz and 5 GHz WiFi coverage and maximum range? here. https://pubs.opengroup.org/onlinepubs/9699919799.2018edition > All functions that open one or more file descriptors shall, unless specified otherwise, atomically allocate the lowest numbered available file descriptor.