4 ms·

> 99% Your figure is too high. Commercial relational databases, many open source databases and widely used file systems are all sufficient. Oracle, SQL Serve

> 99% Your figure is too high. Commercial relational databases, many open source databases and widely used file systems are all sufficient. Oracle, SQL Server, DB/2, PostgreSQL and MySql/MariaDB (with InnoDB) are all ACID systems and recover from crash consistent backups fine. Ext4, XFS, NTFS, etc. are all sufficient file systems, unusually in default form. Reliable storage devices are widely available. Many applications designed around these platforms use COMMIT properly. When they're don't quiescing the database probably won't help with backups anyhow; all you're doing is deferring writes and if the application is not ACID then you can still lose. The database itself, however, will recover and since we're tossing probabilities around, that's 99% of the battle.

blibble 4y ago
I'd bet quite a large amount of money that if you could see every process running on every server on earth: less than 1% of the total would be database processes meanwhile most of the rest seek randomly in files, buffer and write data without calling ever fsync, or append without a pointer and appropriate write barriers (I'm looking at you journald)
- topspin 4y ago
  I don't know what your basis of measurement is, so I'll continue to ignore your ratios. Tolerance of crash consistent state isn't exclusive to databases. Filesystems themselves are often designed to tolerate, for example, sudden power loss without corruption. Applications that manage large collections of files can also achieve this; maildir is an example of such a scheme. All of these systems are using related principles of consistency, and all of them can be correctly backed up by copying volume snapshots.
  - blibble 4y ago
    are you ignoring the main point too, or simply missing it entirely (repeatedly)? the fact there exist some applications (databases, applications using maildir) that correctly use write barriers doesn't mean all applications are always consistent on disk

blibble 4y ago

I'd bet quite a large amount of money that if you could see every process running on every server on earth: less than 1% of the total would be database processes meanwhile most of the rest seek randomly in files, buffer and write data without calling ever fsync, or append without a pointer and appropriate write barriers (I'm looking at you journald)

topspin 4y ago
I don't know what your basis of measurement is, so I'll continue to ignore your ratios. Tolerance of crash consistent state isn't exclusive to databases. Filesystems themselves are often designed to tolerate, for example, sudden power loss without corruption. Applications that manage large collections of files can also achieve this; maildir is an example of such a scheme. All of these systems are using related principles of consistency, and all of them can be correctly backed up by copying volume snapshots.
- blibble 4y ago
  are you ignoring the main point too, or simply missing it entirely (repeatedly)? the fact there exist some applications (databases, applications using maildir) that correctly use write barriers doesn't mean all applications are always consistent on disk