The attached patch seems to do it. The thinking-out-loud patch in my
earlier email wasn't right (I'd kept an interim edit from the
PRAGMA-based approach).
I can't think of a reason to have EXCLUSIVE as the default.
-scott
On 10/10/07, Scott Hess <[EMAIL PROTECTED]> wrote:
> On 10/10/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> > "Scott Hess" <[EMAIL PROTECTED]> wrote:
> > > We've just had a bit of discussion on the Google Gears team about some
> > > cases where failure of an UPDATE/DELETE/INSERT while within a
> > > transaction is unexpected. Well, that and that when you're
> > > multi-threaded you can hit some hard-to-understand cases.
> > >
> > > One suggestion was to use BEGIN IMMEDIATE for explicit transactions,
> > > rather than BEGIN. And it seemed to us like that might be a
> > > reasonable default, given that Gears encourages multiple threads
> > > hitting the same database.
> > >
> > > It looks pretty easy to make this happen (one-line mod to parse.y),
> > > and BEGIN DEFERRED is supported syntax for those who really do mean
> > > that. Does anyone have a strong argument for why we're descending
> > > into a pit of despair by considering this?
> >
> > Many (most?) of the other teams using SQLite in situations
> > similar to Gears have their own separate methods for starting,
> > committing, and rolling back transactions. They don't run
> > BEGIN, COMMIT, or ROLLBACK statements - they call their own
> > built-in methods which in turn runs BEGIN, COMMIT, and
> > ROLLBACK on the user's behalf. If you used this approach,
> > then you could easily revise your method to call BEGIN IMMEDIATE
> > instead of just BEGIN. You could also do the BUSY retry
> > handling that Ken suggests.
>
> Indeed, there has been past discussion about whether we should do some
> sort of transaction API which integrated with the language (for
> instance, automating ROLLBACK on uncaught exceptions). It may be that
> this is the time for that to come back to the fore.
>
> > If you really want to use SQL instead of a separate method,
> > I would suggest a compile-time switch to make IMMEDIATE the
> > default in place of DEFERRED - not a pragma. We already have
> > way too many pragmas. I will be happy to add a compile-time
> > option to make IMMEDATE the default behavior. I will require
> > rather more convincing to add another pragma.
>
> That's a reasonable position to take. For Gears, it would be super
> easy to just make the change directly to parse.y, and I _think_ that I
> understand things well enough to implement
> SQLITE_TRANSACTION_DEFAULT_IMMEDIATE or something along those lines.
>
> Thinking out loud, it looks to me like the change would be something like:
>
> cmd ::= BEGIN transtype(Y) trans_opt. {sqlite3BeginTransaction(pParse, Y);}
> trans_opt ::= .
> trans_opt ::= TRANSACTION.
> trans_opt ::= TRANSACTION nm.
> %type transtype {int}
> + %ifdef SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
> + transtype(A) ::= . {A = TK_IMMEDIATE;}
> + %endif
> + %ifndef SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
> transtype(A) ::= . {A = 0;}
> + %endif
> transtype(A) ::= DEFERRED(X). {A = @X;}
> transtype(A) ::= IMMEDIATE(X). {A = @X;}
> transtype(A) ::= EXCLUSIVE(X). {A = @X;}
> cmd ::= COMMIT trans_opt. {sqlite3CommitTransaction(pParse);}
> cmd ::= END trans_opt. {sqlite3CommitTransaction(pParse);}
> cmd ::= ROLLBACK trans_opt. {sqlite3RollbackTransaction(pParse);}
>
> I can wrap that up better tomorrow. And maybe even think of a better
> define than SQLITE_TRANSACTION_DEFAULT_IMMEDIATE :-).
>
> -scott
>
Index: src/parse.y
===================================================================
RCS file: /sqlite/sqlite/src/parse.y,v
retrieving revision 1.234
diff -u -r1.234 parse.y
--- src/parse.y 21 Aug 2007 10:44:16 -0000 1.234
+++ src/parse.y 11 Oct 2007 17:39:57 -0000
@@ -113,7 +113,12 @@
trans_opt ::= TRANSACTION.
trans_opt ::= TRANSACTION nm.
%type transtype {int}
+%ifdef SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
+transtype(A) ::= . {A = TK_IMMEDIATE;}
+%endif SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
+%ifndef SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
transtype(A) ::= . {A = TK_DEFERRED;}
+%endif SQLITE_TRANSACTION_DEFAULT_IMMEDIATE
transtype(A) ::= DEFERRED(X). {A = @X;}
transtype(A) ::= IMMEDIATE(X). {A = @X;}
transtype(A) ::= EXCLUSIVE(X). {A = @X;}
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