Whilst Time Machine does not do snapshots how enterprise storage do
snapshots, literally a freeze and recovery point. Time Machine does make
backups suitable for booting from. Apple considers Time Machine suitable
for home use backups.
You can backup with TimeMachine and boot from it. My personal experience
of TM is that its flaky and unreliable and we use Carbon Copy Cloner AND
Chronosynd to get to backups that I trust to work. YMMV
However we are going off the point from the OP. I personally think TM is
to blame and would advice the users to check the TM setup and experiment
with delaying the WAL backup just to see what would happen.
Rob
On 12 Dec 2018, at 16:58, Peter da Silva wrote:
Apple uses Sqlite in a number of applications, including Apple Mail,
so
they have to have some kind of accommodation for saving sqlite
databases.
The Time Machine patent does not describe using file system snapshots:
*"An algorithm or other monitoring can be used to detect changes that
occur
during the backup operation in order to maintain consistency between
related data in the backup. The back up can be performed again for
related
data that was modified during prior backup operation. *
*"In general, in one aspect, a method is provided. A backup operation
of
data including a plurality of related items is initiated.
Modifications to
one or more items of the plurality of related items are monitored for
during the backup operation. The backup operation is completed. If a
modification occurred to one or more items, a second backup operation
is
performed for the modified items."*
This does not seem to authoritatively state that multiple files will
be
backed up consistently.
On Wed, Dec 12, 2018 at 9:06 AM Keith Medcalf <kmedc...@dessus.com>
wrote:
I know nothing about "Time Machine", but does it copy the entire
filesystem in (at least) "crash consistent" state?
---
The fact that there's a Highway to Hell but only a Stairway to Heaven
says
a lot about anticipated traffic volume.
-----Original Message-----
From: sqlite-users [mailto:sqlite-users-
boun...@mailinglists.sqlite.org] On Behalf Of Daniel Alm
Sent: Tuesday, 11 December, 2018 05:02
To: sqlite-users@mailinglists.sqlite.org
Subject: [sqlite] Mac: Users receive "database disk image is
malformed" errors after restoring database from Time Machine backup
Hi,
For the past half year we’ve been receiving reports from users who
had restored their SQLite-based databases from a Time Machine
backup.
Afterwards, they would receive "database disk image is malformed”
errors. The app also backs up the user’s data “manually” to a
ZIP
file every week; those backups seem to be working fine. We also
haven’t received reports from other backup tools causing issues. I
have also suspected a bug in Time Machine, but it is striking that
the issues did seem to start occurring after an update to the app
(luckily, in fact, with the same update that also introduced the
“manual” backups).
Changes that we made to our setup in the update that coincided with
the errors occurring:
- Upgraded SQLite from 3.21 to 3.24 (we have since reverted to
3.23.1
in another update; no improvement).
- Used memory mapping for read accesses via “PRAGMA mmap_size =
1073741824;” (we have since reverted to “PRAGMA mmap_size =
0;” after
reading http://sqlite.1065341.n5.nabble.com/Re-Database-corruption-
and-PRAGMA-fullfsync-on-macOS-td95366.html
<http://sqlite.1065341.n5.nabble.com/Re-Database-corruption-and-
PRAGMA-fullfsync-on-macOS-td95366.html>; no improvement).
- Using a secondary database via [ATTACH
DATABASE](https://www.sqlite.org/lang_attach.html
<https://www.sqlite.org/lang_attach.html>) (although this also seems
to occur for users without such a database).
At this point, I am at a loss, especially given that SQLite should
be
fairly robust against database corruption. While our app is running
in the background all the time, it is not very write-heavy (~ one
transaction per minute taking just a few milliseconds). Also, the
app
had been running fine before the update for a long time without any
reports of this issue. I might be doing something wrong or have
changed anything else, but I don’t know what; if you have any
ideas,
let me know.
Any suggestions on what could be the culprit or what else I could
try
besides downgrading all the way to SQLite 3.21 would be appreciated.
Thanks,
Daniel Alm
P.S.: Our database currently uses the following PRAGMAs:
PRAGMA mmap_size = 0;
PRAGMA page_size = 4096;
PRAGMA cache_size = -10240;
PRAGMA foreign_keys = ON;
PRAGMA journal_size_limit = 8388608;
PRAGMA checkpoint_fullfsync = 1;
PRAGMA wal_autocheckpoint = 2048;
PRAGMA journal_mode = WAL;
Happy to provide any more details as needed.
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