[yunqa.de] Re: How to correctly avoid 'database is locked' in multi user environment
- From: Delphi Inspiration <delphi@xxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Thu, 10 Jan 2013 14:49:14 +0100
On 10.01.2013 10:52, H M wrote:
> 1. Is it sufficient to do something like
>
> sqlite3_busy_timeout(FDb, 3000);
>
> once only, each time the database is opened, or does it have to be done
> every time a piece of writing sql is executed?
Yes. Call sqlite3_busy_timeout() once per open database handle.
> 2. is it better to use sqlite3_busy_timeout with a very large value
> (around 10 seconds) or not to use it at all and to use code along the
> lines of the following to retry for as long as necessary (maybe with
> some protection against an indefinite loop)
>
> writeOK := false;
> repeat
>
> try
>
> <execute the writing sql>
> writeOK := true;
>
> except
>
> on e: ESQLITE3 do
> if e.ErrorCode= SQLITE_BUSY then
>
> writeOK := false;
>
> end
>
> until writeOK = true;
Do not wait forever or your application might stall. Also, your
application users would probably like some feedback if nothing happens -
even if it is "The database is currently busy. Please try again later".
For this I'd go for a reasonable sqlite3_busy_timeout() value. You can
also set up your custom busy handler with sqlite3_busy_handler(). Again,
this is set up just once for each database handle.
> 3. Am I correct in thinking that multiple reads (select sql) can be
> going on simultaneously in a multi user environment?
Yes. I suggest reading the pages at
DISQLite3.chm -> SQLite3 Documentation -> Atomic Commit
for a better understanding of concurrent reads and writes.
WAL mode usually improves concurrency over the rollback journal so I
suggest you try that, too.
And last but not least, keep both your read and write transactions as
short as possible.
> 4. There are several references in this mailing list to the DISQLite3
> HTML help file but I cannot seem to find it anywhere on my hard drive. I
> have lots of demo programs and source files but no .htm or .html file.
> Am I misunderstanding or it it located somewhere else?
The DISQLite3.chm file is located right at the root folder where you
extract your DISQLite3 archive:
DISQLite3_Extract\DISQLite3.chm
DISQLite3_Extract\Demos\...
Ralf
_______________________________________________
Delphi Inspiration mailing list
yunqa@xxxxxxxxxxxxx
//www.freelists.org/list/yunqa
Other related posts:
