Thanks Chuck and Robert.
I'm currently catching, reverting and otherwise ignoring the exception
being thrown. I just didn't know if there was anything else I should
have been doing. I appreciate your time and help on this issue.
- Eric
On 12/2/05, Chuck Hill <[EMAIL PROTECTED]> wrote:
> Eric,
>
> As far as I know there is only one certain way to do this:
>
> 1. Add a unique constraint on descriptor in NewKeyword in the DB if
> you don't have one already
> 2. Keep the existing checks in place as they will catch much of the
> attempts at duplication
> 3. When a NewKeyword is saved, wrap the call to saveChanges() in an
> try...catch and catch EOGeneralAdaptorException
> 4. When you get an EOGeneralAdaptorException, inspect it to see if it
> is a violation of the unique constraint. If so, revert the EC and go
> on your way.
>
> Also, noticed that you checking for duplicates below only in
> NewKeywords and not also in the existing ones. You have probably
> handled that elsewhere, but I thought I would mention it.
>
>
> Regards,
> Chuck
>
>
> On Dec 2, 2005, at 11:01 AM, Eric Stewart wrote:
>
> > Chuck,
> >
> > You are right on all accounts.
> >
> > Here's a little broader understanding of the system. It's a content
> > finder, storage and retrieval system based on keywords. A client (a
> > client in general terms not Java client, be it browser or other
> > script) queries the system using a URL with the keyword in it (which
> > hits a direct action). The system then tries to reply with whatever
> > content it knows about that keyword.
> >
> > If the system has never seen the keyword, it is then stored in a
> > "NewKeyword" table which is basically operating as a stack for finding
> > content for keywords it's not aware of. Once an hour another
> > application is fired off via cron and a direct action which then
> > starts popping keywords out of the new keyword table, finds content
> > for them via spidering and saves the keyword and data into the
> > permanent keyword store tables. Then the system will be able to
> > provide content for that particular keyword from that point on.
> >
> > This system has over 4.5 million keywords and recieves on average 2
> > million request a day.
> >
> > But as I said, some sort of race condition is happening. I can't
> > figure out how to only make sure a new keyword isn't entered into the
> > new keyword table more than once.
> >
> > - Eric
> >
> > On 12/2/05, Chuck Hill <[EMAIL PROTECTED]> wrote:
> >> Hi Eric,
> >>
> >> I am not sure that I am following this correctly, so some questions
> >> below.
> >>
> >>
> >> On Dec 2, 2005, at 8:26 AM, Eric Stewart wrote:
> >>
> >>> Hello everyone,
> >>>
> >>> I'm having a problem where it appears I'm getting stale data from
> >>> the
> >>> editing context.
> >>>
> >>> I have a direct action that is inserting keywords into a database
> >>> table. The word itself (called "descriptor") is unique because I
> >>> don't
> >>> want the same keyword in the system twice.
> >>>
> >>> When a direct action request comes in for information about that
> >>> keyword, I check to see if that keyword is already in the system. If
> >>> not I add it.
> >>>
> >>> Here is the code I use to check for that keyword.
> >>>
> >>> /**
> >>> * Determines whether a new keyword with the given
> >>> descriptor is
> >>> present in the system.
> >>> */
> >>> public static boolean isPresentByDescriptor
> >>> (EOEditingContext ec,
> >>> String descriptor) {
> >>> NSDictionary args = new NSDictionary(descriptor,
> >>> "descriptor");
> >>> EOQualifier qual =
> >>> EOQualifier.qualifierToMatchAllValues(args);
> >>> EOFetchSpecification fs = new EOFetchSpecification
> >>> ("NewKeyword",
> >>> qual, null);
> >>>
> >>> // Make sure we fetch fresh data
> >>> fs.setRefreshesRefetchedObjects(true);
> >>>
> >>> // Find the keyword matching value
> >>> NSArray keywords = ec.objectsWithFetchSpecification
> >>> (fs);
> >>> if (keywords.count() == 0) {
> >>> // No match found
> >>> return false;
> >>> } else if (keywords.count() > 1) {
> >>> // More than one match found
> >>> if (NSLog.debugLoggingAllowedForLevel
> >>> (NSLog.DebugLevelCritical)) {
> >>> NSLog.debug.appendln("Duplicate new
> >>> keyword found matching: " +
> >>> descriptor);
> >>> }
> >>> return true;
> >>> } else {
> >>> // Match found return the keyword
> >>> return true;
> >>> }
> >>> }
> >>>
> >>> What is happening is I'm getting a lot of exceptions complaining
> >>> that
> >>> a keyword being added to the system is not unique, hence I can only
> >>> guess that data from the EC is stale and is not reflecting newly
> >>> inserted keywords.
> >>>
> >> By exception do you mean the debug message above, a unique constraint
> >> violation on the database, or something else?
> >>
> >>
> >>
> >>> This direct action is running on an application that has around 20
> >>> instances running. So some how one of the other instances is
> >>> inserting
> >>> a new keyword and the other instances continue to report it as not
> >>> being there.
> >>>
> >>
> >> You could have a race condition where two instances check the
> >> database for the same keyword, and see that it is not there. They
> >> they both insert it. The second one to commit will (attempt to)
> >> duplicate the value in the database. Is that what you are seeing?
> >> You can even see this on a single instance if you are dispatching
> >> requests concurrently.
> >>
> >>
> >>> Should I be using EditingContext.refaultAllObjects() or will this
> >>> not
> >>> solve my problem. What I don't want to happen is for this to
> >>> severely
> >>> degrade the performance of the application. I think I remember
> >>> EditingContext.invalidateAllObjects() causing a pretty poor
> >>> performance on high load applications, which this is. Is there some
> >>> other way to check whether the keyword is in the system or not
> >>> before
> >>> it's added without incurring such a severe penalty?
> >>>
> >> I would not suggest any of those solutions. Are the instances
> >> actually changing the descriptor of NewKeywords, just only inserting
> >> new ones? If they are only inserting new ones, there should not be
> >> an issue with actual stale data the way you are fetching it. I
> >> suspect your problem may lie elsewhere.
> >>
> >>
> >>> Is there anyway to refault JUST the data in a certain table or of a
> >>> certain type of EO and not all the data in an EditingContext.
> >>>
> >> You can do it object by object, but again, that does not seem to be
> >> the problem (or I am misunderstanding your situation).
> >>
> >> Chuck
> >>
> >> --
> >> Coming in 2006 - an introduction to web applications using WebObjects
> >> and Xcode http://www.global-village.net/wointro
> >>
> >> Practical WebObjects - for developers who want to increase their
> >> overall knowledge of WebObjects or who are trying to solve specific
> >> problems. http://www.global-village.net/products/
> >> practical_webobjects
> >>
> >>
> >>
> >>
> >>
> >
>
> --
> Coming in 2006 - an introduction to web applications using WebObjects
> and Xcode http://www.global-village.net/wointro
>
> Practical WebObjects - for developers who want to increase their
> overall knowledge of WebObjects or who are trying to solve specific
> problems. http://www.global-village.net/products/practical_webobjects
>
>
>
>
>
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