17 Aug
2016
17 Aug
'16
10:10 a.m.
Thank you Thomas for your explanations.
You are completely right, you wrote it in the first mail. The generation of
the cache key is broken. I added now XWIKI-13632 for this.
If it is ok, I start preparing a PullRequest for XWIKI-13632 and then
a second one for XWIKI-13623.
Kind regards,
Fabian
2016-08-10 16:33 GMT+02:00 Thomas Mortagne <thomas.mortagne(a)xwiki.com>om>:
On Wed, Aug 10, 2016 at 12:41 PM, Fabian Pichler
<fabian.pichler(a)synventis.com> wrote:
right
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ok, if I understand correctly the API contract so
far is, that the
context
defines the database used and the reference of
the document to load
must only be taken relative to the given context. (old String fullName
and context-database interpretation).
Yes.
So, I think it would be better to compute the lookup key based on the
context database and the fullName computed out of the document reference.
Otherwise you would not get the same document in both situations.
1. from cache
2. freshly loaded
Yes this what I explained.
Anyway, I am not sure if it is a good idea to fix the key-issue as part
of
XWIKI-13623. I think that XWIKI-13623 should only
focus on the mentioned
memory visability and resulting data loss issue.
I did not told you to do it as part of XWIKI-13623 but you cannot do
XWIKI-13623 without cleaning a bit the way cache key is handled right
now in the method since from what I understood you depend on a proper
cache key (to access the right DocumentLoader) in the solution you
proposed.
Fabian.
2016-08-10 10:52 GMT+02:00 Thomas Mortagne <thomas.mortagne(a)xwiki.com>om>:
> On Wed, Aug 10, 2016 at 10:14 AM, Fabian Pichler
> <fabian.pichler(a)synventis.com> wrote:
> > Hi Thomas
> >
> > Thanks for responding and thanks for supporting the suggested
solution.
> >
> > I understand the doc.Key-issue that you mentioned. Yet, I think this
is
> not
> > a
> > XWikiCacheStore#loadXWikDoc concern. In my understanding the expected
> > document
> > to load is defined by the document-reference and the language. Thus
the
> > Hibernate-Store must be concerned in
setting the context database
> according
> > to the Wiki-Reference before loading the document. This is acctually
> already
> > done in the XWiki#getDocument call. I agree that this might be the
wrong
> > place to do it.
> > Thus, I would suggest to fix this issue in the XWikiHibernateStore on
a
> > seperate jira-issue.
>
> In an ideal world it would be fixed in XWikiHibernateStore I agree but
> this would break retro compatibility (yeah always a pain). That's why
> I talked about providing a new API.
>
> So right now in practice using a combination of context wiki and
> document reference is part of the API definition and can be applied at
> XWikiCacheStore too.
>
> Note that in practice this is actually a pretty rare case since anyone
> is supposed to use XWiki#getDocument which make sure the context
> contain the document wiki. But this can still happen since this is a
> very old and public API.
>
> > Maybe this could be combined with a significant performance
improvment
in
> > loading
> > the documents with fewer sql-queries per loading action.
> >
> > With XWIKI-13623 I try to tackle the issue about randomly loosing
> BaseObject
> > data because of an not thread safe construction and publication of
> > XWikiDocument
> > java objects in XWikiCacheStore. Because this issue gave us a big
> headache
> > in
> > production multiple times, I solved it in our project in the way
> mentioned.
> >
> > If the xwiki-dev team supports the suggested solution, I would be
willing
> to
proceed
> and prepare a pull request for an adapted XWikiCacheStore fix.
>
> Kind regards,
> Fabian
>
>
> 2016-08-08 12:07 GMT+02:00 Thomas Mortagne <thomas.mortagne(a)xwiki.com
:
> >
> >> XWikiCacheStore#loadXWikiDoc is actually a bit tricker than that > >> now for retro compatibility and
laziness (really need to rewrite this
> >> whole store API) reasons and before applying what you propose the way
> >> it deals with document uid should be modified a bit.
> >>
> >> Hibernate store is always loading the document from the wiki
indicated
> >> in the context completely ignoring
the wiki in the XWikiDocument
> >> object. That means that doc.getKey() may be different than the key of
> >> the document that will actually come from the hibernate store. So
> >> before adding DocumentLoader jingling a first thing to do is generate
> >> the initial cache key with a mix of the wiki id located in the
context
> >> and the XWikiDocument reference.
> >>
> >> Then what you propose sounds good.
> >>
> >> On Mon, Aug 8, 2016 at 8:53 AM, Fabian Pichler
> >> <fabian.pichler(a)synventis.com> wrote:
> >> > Hi devs
> >> >
> >> > http://jira.xwiki.org/browse/XWIKI-13623
> >> > I would like to discuss the suggested solution, before I start
> >> implementing
> >> > it:
> >> >
> >> > *I suggest the following solution:*
> >> > Introducing a nested DocumentLoader class which loads the document
> >> calling
> >> > the basestore loadXWikiDoc in a synchronized getDocOrLoad method.
The
> >> > DocumentLoader objects gets
instantiated in the cacheStore on a
cache
> >> miss.
> >> > It then gets stored in a ConcurrentHashMap using the same key
which is
> >> used
> >> > for the document cache (DocumentReference including language).
Using
> >> > putIfAbsent to insert the
DocumentLoader and calling the
synchronized
> >> load
> >> > method on the object in the map solves the memory visibility issue
and
> >> > moreover ensures that the same
XWikiDocument is not loaded multiple
> times
> >> > concurrently from the database. It is still possible to load
different
> > documents in parallel. A DocumentLoader will
load the XWikiDocument
only
> > once and the returns the identical
document object on any following
call
> of
> > the synchronized getDocOrLoad method.
> >
> > WDYT?
> >
> > Kind Regards,
> > Fabian
> > _______________________________________________
> > devs mailing list
> > devs(a)xwiki.org
> > http://lists.xwiki.org/mailman/listinfo/devs
>
>
>
> --
> Thomas Mortagne
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>
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