Re: Snapshots mysteriously vanishing?
Re: Snapshots mysteriously vanishing?
- Subject: Re: Snapshots mysteriously vanishing?
- From: Alexis Tual <email@hidden>
- Date: Wed, 3 Nov 2010 13:11:08 +0100
Hi and thanks for your detailed answer,
just adding my 2ct :
we've got the same errors in the same environment : deep nested editing context's. (WO 5.3 + Wonder, don't know about 5.4 though)
At that time, the only workarounds we found were :
- when possible, reducing the level of nested (basically only 1 level of nested ec)
- or as someone mentioned, using parentEC.setRetainsRegisteredObjects(true)
Cheers,
Alex
Le 3 nov. 2010 à 11:39, Sobanski, Jedrzej a écrit :
> Hi,
>
> After spending quite some time on similar problem I would like to share what solved the issue in my case.
>
> ENVIRONMENT
> We had a scenario that ALWAYS caused this to happen. There was too much code to make it a separate app, but basically it involved inserting, updating and deleting objects, with nesting editing contexts up to 2 levels deep several times. Whenever we saved changes in nested editing context, it was no longer used and simply abandoned (so never saved changes twice on the same EC). Application never crashed on saving changes in nested editing context, but did always crash at the end of the test scenario when saving changes in the root editing context. I tried to reduce our test scenario, but removing some of test steps did only cause the issue to happen more rarely rather than always. Test involved just bunch of operations and none of them appeared to be crucial or unneeded. Root EC was locked in Session#awake() and unlocked in Session#sleep(). It didn't matter whether we were using EODatabaseContext or ERXDatabaseContext. Code (probably) didn't violate any of EOF commandments or at least I wasn't able to find such (or I fixed them where I'd found such violations).
>
> The only EO related properties set are
> er.extensions.ERXEnterpriseObject.updateInverseRelationships=false
> er.extensions.ERXEnterpriseObject.applyRestrictingQualifierOnInsert=true
> I'm not sure if those had any importance for this issue.
>
> EXCEPTIONS
> Problem was revealing itself in two ways:
> a) java.lang.IllegalStateException: rowDiffsForAttributes: snapshot in com.webobjects.eoaccess.EODatabaseOperation {_dbSnapshot = {}; ....
> b) ObjectNotAvailableException: No ... found with globalID: ...
>
> In both cases cause was the same - _dbSnapshot was null at some point, while it shouldn't. Sometimes, depending on the order of operations happening when saving changes, EOEditingContext did change that _dbSnapshot value from null to an empty array and that's why we were getting sometimes two different exceptions for the same scenario which implies that both errors have common cause.
>
> WHAT SOLVED IT IN MY CASE
> I spent quite some time on it trying to find the root cause, though none of advices I was able to find, did help. Eventually disposing each nested editing context after saving its changes (in my case they were not used anymore) solved this issue.
>
> --
> Regards,
> Jedrzej Sobanski
>
> On Apr 1, 2010, at 7:03 PM, Chuck Hill wrote:
>
>
> On Apr 1, 2010, at 5:24 AM, Marc Guenther wrote:
>
> Hi all,
>
> I spent quite some time now on this problem. I found a way to
> reproduce it, still I have no idea what to do about it.
>
> Can you share what that is?
>
>
> What I don't understand, if this is a known bug, and people are
> actually experiencing it, why have I never heard about it, and why
> is there no fix? This seems to be a major problem.
>
> I also found, that this also happens on WO5.2.3, which makes it even
> worse. I wonder why it has never bitten us before. Or maybe it has,
> but now some customer discovered some peculiar workflow which
> triggers this more often than usual.
>
>
> I don't recall seeing anything like this for a long time. I suspect
> that your customer theory may be true.
>
>
> Chuck
>
>
>
> James and Johann, (or everyone who has this problem), which version
> of WO are you using? Are we all talking about 5.4.3 here?
>
> On 25.03.2010, at 21:38, Mike Schrag wrote:
> I don't have a patch you can easily apply. The workaround on your
> side is to not let the EO in the parent EC garbage collect
> (basically, keep a reference to the parent EO around for any EO
> that you fault into child EC).
>
> Would a parentEC.setRetainsRegisteredObjects(true) help?
>
> Also there is a EODatabaseContext.disableSnapshotRefCounting()
> method, which completely disabled the refcounting mechanism. But I
> guess that would run out of memory very fast?
>
> There's not an easy recovery from this -- you have to toss your EC
> stack ... or .. maybe you could refetch the snapshot underneath it,
> but i think you're probably left with a __retainCount of -1 at that
> point, so probably even that won't help you.
>
> No, I don't want this to occur at all :)
>
> Have a happy easter,
> Marc
>
> I think this could be fixed pretty easily in wonder by overriding
> ERXGenericRecord.__setRetainCount .. When count is set >0, call
> back to your EC and retain the object in a dict and when it drops
> to 0, release that ref.
>
> On Mar 25, 2010, at 4:25 PM, Brook, James wrote:
>
> Mike,
>
> That sounds all too familiar to me. We are experiencing errors
> just like that. We have a feature that creates nested editing
> contexts several levels deep and fetches EOs all the way down to
> the bottom. Do you know of a workaround, patch or some way to
> recover from the bug you mention? I seem to remember a similar bug
> years ago in the days when EOF kept strong references. We are
> using Wonder.
>
> Sorry for selfishly jumping in. Disappearing snapshots are causing
> us lots of pain because whole instances of our application become
> useless.
>
> --
> James
> ________________________________________
> From: webobjects-dev-bounces
> +jbrook=email@hidden<mailto:+jbrook=email@hidden> [webobjects-dev-bounces+jbrook=email@hidden
> ] On Behalf Of Mike Schrag [email@hidden]
> Sent: 25 March 2010 20:20
> To: Marc Guenther
> Cc: email@hidden<mailto:email@hidden>
> Subject: Re: Snapshots mysteriously vanishing?
>
> by any chance was this an EO in a parent editing context that
> also existed in a child editingcontext?
>
> I don't think so, but I'm not sure. That particular EO could have
> been in all differents ECs at the time, as it's entity is used
> all over the place.
>
> Do you have anything specific in mind?
> yeah, there's a bug with refcounting of eo's in child ec's if the
> parent ec copy of the EO gets garbage collected ... the result of
> this bug is disappearing snapshots. this specifically applies to
> eo's fetched into a child that were already fetched into the
> parent, though, not to peer ec's.
>
> ms
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> --
> Chuck Hill Senior Consultant / VP Development
>
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