Re: [sqlite] Open the database - Creating the empty database

[Roger Binns]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Joanne Pham wrote:
> The problem here is the database is not created but if the second process has 
>tried to access the database then the empty database is created which
has the size of 0.

If you use sqlite3_open_v2 then you can specify flags for creation.
http://sqlite.org/c3ref/open.html

However you still have a race condition as the first process may not
have got around to creating a schema/content etc before the second tries
to read the database.

Roger
-BEGIN PGP SIGNATURE-
Version: GnuPG v1.4.9 (GNU/Linux)

iEYEARECAAYFAklGqcYACgkQmOOfHg372QRwtgCgjlkWDneHVbNPfD96S/oXwrRi
dBMAoLL1u5GTo8vGjY/GkD+hrb7HkSxC
=cKYG
-END PGP SIGNATURE-
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users

Re: [sqlite] Open the database - Creating the empty database

[Derrell Lipman]

On Mon, Dec 15, 2008 at 1:43 PM, P Kishor  wrote:

> On 12/15/08, Joanne Pham  wrote:
> > Hi All,
> >  I have this problem about open the database. Here is the detail about
> the problem.
> >
> >  Our application have one process to create the database and another
> process to open the database and creating the report.
> >  The problem here is the database is not created but if the second
> process has tried to access the database then the empty database is created
> which has the size of 0. So the question is there any way the open database
> API should return an error message instead of creating the empty database
> when the second process opens the database.
> >
> >  Thanks,
>
>
> A SQLite database is just a file on the hard disk. Test for the
> existence of the file before trying to open it.
>

That is, unfortunately, a recipe for race conditions.  Application A tests
for whether the file exists and finds it doesn't.  The operating system task
switches to Application B which had previously determined that the file
doesn't exist, and now creates it and adds some data.  Task switch back to
Application A which assumes that the file doesn't exist (since it had
previously determined that) and scribbles over the data just written by
Application B.

An alternative is to open the database normally (sqlite3_open) and issue the
queries

  BEGIN EXCLUSIVE;
  SELECT 1 FROM sqlite_master LIMIT 1;

If you get back a value (1), then the database had already has tables (or
triggers or ...) in it.  If you get back NULL then you can go ahead and
create the database tables et al.  When done creating tables and doing
whatever else you need to do before allowing other applications access,
issue a COMMIT.  Since you had an exclusive transaction, any other
application trying to determine if the database is available or not will
block until your transaction completes.

Derrell
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users

Re: [sqlite] Open the database - Creating the empty database

[Joanne Pham]

Thanks for the respond.
I will test for the existence of the file before trying to open it.
Once again thanks,
JP






From: P Kishor <punk.k...@gmail.com>
To: General Discussion of SQLite Database <sqlite-users@sqlite.org>
Sent: Monday, December 15, 2008 10:43:57 AM
Subject: Re: [sqlite] Open the database - Creating the empty database

On 12/15/08, Joanne Pham <joannekp...@yahoo.com> wrote:
> Hi All,
>  I have this problem about open the database. Here is the detail about the 
>problem.
>
>  Our application have one process to create the database and another process 
>to open the database and creating the report.
>  The problem here is the database is not created but if the second process 
>has tried to access the database then the empty database is created which has 
>the size of 0. So the question is there any way the open database API should 
>return an error message instead of creating the empty database when the second 
>process opens the database.
>
>  Thanks,


A SQLite database is just a file on the hard disk. Test for the
existence of the file before trying to open it.
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users



  
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users

Re: [sqlite] Open the database - Creating the empty database

[P Kishor]

On 12/15/08, Joanne Pham  wrote:
> Hi All,
>  I have this problem about open the database. Here is the detail about the 
> problem.
>
>  Our application have one process to create the database and another process 
> to open the database and creating the report.
>  The problem here is the database is not created but if the second process 
> has tried to access the database then the empty database is created which has 
> the size of 0. So the question is there any way the open database API should 
> return an error message instead of creating the empty database when the 
> second process opens the database.
>
>  Thanks,


A SQLite database is just a file on the hard disk. Test for the
existence of the file before trying to open it.
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users

[sqlite] Open the database - Creating the empty database

[Joanne Pham]

Hi All,
I have this problem about open the database. Here is the detail about the 
problem.
 
Our application have one process to create the database and another process to 
open the database and creating the report.
The problem here is the database is not created but if the second process has 
tried to access the database then the empty database is created which has the 
size of 0. So the question is there any way the open database API should return 
an error message instead of creating the empty database when the second process 
opens the database.
 
Thanks,
JP


  
___
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users