On 13/3/62 22:51, Simon Slavin wrote:
If the source database is changed while the Online Backup API is running, it
returns to the beginning of the database and starts again. I have a couple of
questions which might be useful, especially if the database is changed only by
the same connection as it performing the backup.
In that case - when the connection doing the backup is the same as the
one that modifies the database - the backup does not restart. Instead,
when the connection writes to the original database, any pages that have
already been copied into the backup are updated there as well.
The backup only has to restart when the connection doing the backup and
the connection doing the db modification are different connections.
From the docs for sqlite3_backup_step():
"If the source database is modified by an external process or via a
database connection other than the one being used by the backup
operation, then the backup will be automatically restarted by the next
call to sqlite3_backup_step(). If the source database is modified by the
using the same database connection as is used by the backup operation,
then the backup database is automatically updated at the same time."
https://www.sqlite.org/c3ref/backup_finish.html#sqlite3backupstep
Dan.
There's a chunk of headers at the beginning of the database which changes
frequently. Ignoring that chunk for a moment ... two questions:
1) Suppose the first page of the source database which is modified is after
the point that the backup has reached. Is it necessary to restart ? Could
this be detected somehow ?
2) Suppose the first page of the source database which is modified is before
the point that the backup has reached. Could the backup not return just to
that point rather than to the very beginning ?
As for the chunk of headers at the very beginning of the database, this should
not change size. It could be updated at the end.
I'm perfectly happy to be told that these optimizations cannot be performed for
reasons I don't understand.
Simon.
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