- From: Ian Hickson <ian@hixie.ch>
- Date: Wed, 17 Oct 2007 06:18:38 +0000 (UTC)
On Fri, 5 Oct 2007, Scott Hess wrote:
> >
> > There isn't really a thread-global transaction, the transactions are
> > per-sequence-of-executeSql-calls, as in:
> >
> > executeSql('sql1', function (result) {
> > executeSql('sql2', function (result) {
> > executeSql('sql3', function (result) {
> > // this is all in one transaction
> > });
> > });
> > });
> > executeSql('sql4', function (result) {
> > executeSql('sql5', function (result) {
> > executeSql('sql6', function (result) {
> > // this is all in another transaction
> > });
> > });
> > });
> >
> > ...where the likely order of execution is sql1 and sql4 at the same
> > time, then sql2 and sql5, then sql3 and sql6, assuming all the
> > statements take the same amount of time.
>
> At least for SQLite, the implicit transaction, as I understand it, would
> result in sql1/2/3 executing in a transaction, and the transaction for
> sql4/5/6 either waiting for the sql1/2/3 transaction to complete, or
> failing due to locking errors. I don't think they can interleave if
> either of them opens a transaction, because SQLite locks at the database
> level.
Indeed, that's also possible.
> In general, I am of the opinion that you should either have no
> transactions, or explicit transactions, but never implicit transactions.
> This is a little different from a case like mysql, where you might make
> an explicit decision to do things without transactions in the interest
> of scalability, with the associated need to be very careful in how your
> system orders your execution. At least for SQLite, having a transaction
> for multiple statements is more efficient than not, and scalability
> isn't a huge issue. Even so, I think that implicit transactions are
> making a decision on behalf of the developer which the developer should
> be explicit about.
What are the disadvantages of implicit transactions?
What do other people think?
> I wasn't clear from the spec, but I think it would be possible to do the
> sequence-of-statements case like:
>
> executeSql('sql1', function (result) {
> closeTransaction();
> executeSql('sql2', function (result) {
> closeTransaction();
> executeSql('sql3', function (result) {
> });
> });
> });
>
> If not, then I think this would be a useful addition (if implicit
> transactions are retained).
Yes, that's possible. Let me know if the spec is still unclear on this; I
tried to clarify it. (I'll be adding examples in due course, by the way.)
> Explicit transactions could be as easy as:
>
> executeSql('sql1', function (result) {
> executeSqlInTransaction('sql2', function (result) {
> // Everything in here is in a transaction.
> executeSql('sql3', function (result) {
> });
> });
> });
That's a possibility, though we're trying to keep the API as thin as
possible.
--
Ian Hickson U+1047E )\._.,--....,'``. fL
http://ln.hixie.ch/ U+263A /, _.. \ _\ ;`._ ,.
Things that are impossible just take longer. `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 16 October 2007 23:18:38 UTC