Many hyperlinks are disabled.
Use anonymous login
to enable hyperlinks.
Overview
Comment: | Add new file doc/F2FS.txt, containing notes on the way SQLite uses the F2FS atomic commit feature. |
---|---|
Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | exp-retry-atomic-commit |
Files: | files | file ages | folders |
SHA3-256: |
59efb1bfaba12742379aae45c8c796ca |
User & Date: | dan 2018-07-16 20:44:00.735 |
Context
2018-07-17
| ||
13:55 | Fix for builds without SQLITE_ENABLE_BATCH_ATOMIC_WRITE. (Closed-Leaf check-in: b10ec14ef7 user: dan tags: exp-retry-atomic-commit) | |
2018-07-16
| ||
20:44 | Add new file doc/F2FS.txt, containing notes on the way SQLite uses the F2FS atomic commit feature. (check-in: 59efb1bfab user: dan tags: exp-retry-atomic-commit) | |
2018-07-14
| ||
20:25 | If an SQLITE_IOERR error is encountered as part of an atomic commit on an F2FS file-system, retry the commit in legacy journal mode. (check-in: 1c41250f67 user: dan tags: exp-retry-atomic-commit) | |
Changes
Added doc/F2FS.txt.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 | SQLite's OS layer contains the following definitions used in F2FS related calls: #define F2FS_IOCTL_MAGIC 0xf5 #define F2FS_IOC_START_ATOMIC_WRITE _IO(F2FS_IOCTL_MAGIC, 1) #define F2FS_IOC_COMMIT_ATOMIC_WRITE _IO(F2FS_IOCTL_MAGIC, 2) #define F2FS_IOC_START_VOLATILE_WRITE _IO(F2FS_IOCTL_MAGIC, 3) #define F2FS_IOC_ABORT_VOLATILE_WRITE _IO(F2FS_IOCTL_MAGIC, 5) #define F2FS_IOC_GET_FEATURES _IOR(F2FS_IOCTL_MAGIC, 12, u32) #define F2FS_FEATURE_ATOMIC_WRITE 0x0004 After opening a database file on Linux (including Android), SQLite determines whether or not a file supports F2FS atomic commits as follows: u32 flags = 0; rc = ioctl(fd, F2FS_IOC_GET_FEATURES, &flags); if( rc==0 && (flags & F2FS_FEATURE_ATOMIC_WRITE) ){ /* File supports F2FS atomic commits */ }else{ /* File does NOT support F2FS atomic commits */ } where "fd" is the file-descriptor open on the database file. Usually, when writing to a database file that supports atomic commits, SQLite accumulates the entire transaction in heap memory, deferring all writes to the db file until the transaction is committed. When it is time to commit a transaction on a file that supports atomic commits, SQLite does: /* Take an F_WRLCK lock on the database file. This prevents any other ** SQLite clients from reading or writing the file until the lock ** is released. */ rc = fcntl(fd, F_SETLK, ...); if( rc!=0 ) goto failed; rc = ioctl(fd, F2FS_IOC_START_ATOMIC_WRITE); if( rc!=0 ) goto fallback_to_legacy_journal_commit; foreach (dirty page){ rc = write(fd, ...dirty page...); if( rc!=0 ){ ioctl(fd, F2FS_IOC_ABORT_VOLATILE_WRITE); goto fallback_to_legacy_journal_commit; } } rc = ioctl(fd, F2FS_IOC_COMMIT_ATOMIC_WRITE); if( rc!=0 ){ ioctl(fd, F2FS_IOC_ABORT_VOLATILE_WRITE); goto fallback_to_legacy_journal_commit; } /* If we get there, the transaction has been successfully ** committed to persistent storage. The following call ** relinquishes the F_WRLCK lock. */ fcntl(fd, F_SETLK, ...); Assumptions: 1. After either of the F2FS_IOC_ABORT_VOLATILE_WRITE calls return, the database file is in the state that it was in before F2FS_IOC_START_ATOMIC_WRITE was invoked. Even if the ioctl() fails - we're ignoring the return code. This is true regardless of the type of error that occurred in ioctl() or write(). 2. If the system fails before the F2FS_IOC_COMMIT_ATOMIC_WRITE is completed, then following a reboot the database file is in the state that it was in before F2FS_IOC_START_ATOMIC_WRITE was invoked. Or, if the write was commited right before the system failed, in a state indicating that all write() calls were successfully committed to persistent storage before the failure occurred. 3. If the process crashes before the F2FS_IOC_COMMIT_ATOMIC_WRITE is completed then the file is automatically restored to the state that it was in before F2FS_IOC_START_ATOMIC_WRITE was called. This occurs before the posix advisory lock is automatically dropped - there is no chance that another client will be able to read the file in a half-committed state before the rollback operation occurs. |