Thanks to DRH for the quick answer. So I would infer that the sqlite
file header would normally be in a consistent state, and only be in an
inconsistent or otherwise incorrect state in the following cases:
1. modification (write) is in progress (until the sqlite3 code has a
chance to finish the modification)
2. application crashed or otherwise terminated without finishing the
modification (until the application or some other sqlite program opens
the database again)
3. rogue code writes data to the file descriptor in use by sqlite
4. other causes described in http://www.sqlite.org/howtocorrupt.html
such as rogue code, rogue process, rogue script, OS bug, dishonest
My understanding is that iOS applications with shared databases can be
especially sensitive to sqlite headers as discussed in:
- note referenced by SQLCipher project, not sure if I can understand
- discovery that iOS checks header of shared SQLite databases, with
special handling of sqlite databases in WAL mode
I still have the following questions:
- Am I correct to say "that the sqlite file header would normally be
in a consistent state"?
- Am I missing anything or otherwise mistaken here?
- How likely would the header continue to indicate that the database
is an sqlite database in case 1 or 2 above?
- How likely would the header continue to indicate whether the
database is in WAL or any other journal mode in case 1 or 2 above?
- Any recommended explanations or resources that explain how iOS
handles shared sqlite databases (in more detail, with simpler terms)?
- Any recommended explanations or resources to understand how and when
sqlite header may be in inconsistent or otherwise incorrect state?
- Any recommended explanations or resources to understand how it may
be possible to obtain the correct sqlite database information (such as
WAL or other journal mode, actual database size, number of pages,
page/cache size, etc.)?
On Tue, Feb 13, 2018 at 9:10 AM, Richard Hipp <d...@sqlite.org> wrote:
> On 2/13/18, Chris Brody <chris.br...@gmail.com> wrote:
> > I was wondering what would happen if there would be an application crash,
> > system crash, or power failure while SQLite is updating the file header?
> > Did I miss an explanation somewhere?
> The content is replicated either in the rollback-journal or in the
> write-head log (depending on whether or not you are in WAL mode) and
> will be recovered automatically when the database is first opened
> after power has been restored. See
> https://www.sqlite.org/atomiccommit.html for further information.
> D. Richard Hipp
> sqlite-users mailing list
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