On 17 May 2012, at 4:34pm, Rajesh Kumar <thisiz...@gmail.com> wrote:
> No am not using any PRAGMAs. I just cross compiled sqlite source to
> ARM architecture. Can't I forcefully do commit on my transaction????
If you are correctly using _open() and _close(), and haven't disabled synchrony
with PRAGMAs or compilation settings, then you should be getting COMMIT
automatically. There's no way to force SQLite to flush changes to disk because
SQLite flushes changes to disk as part of normal working.
As for use of COMMIT … every SQL command executed with SQLite is part of a
transaction. So normal programming tends to look like
BEGIN;
… any number of INSERT, DELETE, SELECT, UPDATE commands here …
COMMIT;
By the time SQLite has returned from the COMMIT, your changes should have made
it to disk. There's no flushing to do, SQLite already did it.
If you do happen to issue a SQL command without having issued a 'BEGIN' first,
then SQLite helpfully wraps it in its own transaction for you, executing all of
these
BEGIN (<-- I helpfully do this for you because you forgot)
Your command here
COMMIT (<-- since you forgot the BEGIN you'll probably forget the COMMIT too)
with the single call to sqlite3_exec() you made, and doing the COMMIT before it
returns from processing that call. So even if all you do is use
sqlite3_exec('UPDATE command here'), SQLite has already done all the flushing
to disk that needs doing.
However, the code in SQLite that does the COMMIT includes the C command fsync()
as part of its working. (I think this is right. I haven't read the source
code.) And its the fsync() that does the flushing. So if that's not correctly
implemented on your platform (which is depressingly common) then things like
application crashes or power loss can lead to a corrupt database. Which is why
Richard pointed to
http://www.sqlite.org/atomiccommit.html and
http://www.sqlite.org/howtocorrupt.html
Simon.
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