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From "Bruce Li" <...@tirawireless.com>
Subject Jackrabbit = Big Trouble??
Date Thu, 26 Jul 2007 22:23:52 GMT
I have been in this Jackrabbit Community for a couple of months since I joined repository project
two months ago.

 

First, I respect and appreciate all hard works contributed in current JackRabbit project and
definitely I am sure a lot of developers benefit from this project. There are some people
contribute their JackRabbit working experience like David Nuescheler, who collects "7 DR Rules",
which is precious since current lack of document of JackRabbit, and they are "real" working
experiences. 

 

However, I also heard some negative voice from this community like "JackRabbit is dead (for
us)" from Frédéric Esnault. I suffer some troubles from JackRabbit and it seems foundational
problems. I would like to share all my experience with you, and any feedback or good suggestion
is definitely what I want.

 

Since these troubles are "big" troubles for enterprise use of JackRabbit 1.3, let's discuss
it from beginning.

 

Question 1: 

Why do you select JackRabbit rather than Database as your repository solution?

 

There are a lot of answers for this question and it seems that everybody who joins this community
has already known the answers (It may be formal document which was approved by your CTO).
 However, my opinion, this is the basic question really need to be discussed here.

 

To answer this question, some technical key words to support Jackrabbit may be "JCR API",
"Lucene Search Engine" and so on. However, as the user of JackRabbit, I would like to list
the two key concerns why I select JackRabbit as repository solution from Product Point of
View:

 

1.	Quick and effective data search/fetch from volume content repository
2.	Build-in content version/revision control without extra code

 

Now let me describe the big troubles I met in my use: 

1.	Quick and effective data search or fetch from volume content repository

 

Experience: There are not many data on my repository which contains hundreds of two major
object nodes, each node (object) contains less than 20 properties (fields), including the
other 5 child nodes (nested small objects) and one of two major nodes(object) has one binary
data (up to 1 megabyte). Unfortunately, the performance is not acceptable when I navigate
nodes of the major nodes. The main problem is the build-in Cache Manager of JackRabbit resizes
which costs uncertain time, which result the operation very slow sometimes.  It is not easy
to read those codes when debugging Jackrabbit for performance tuning because there is no document
about the logic behind the index resizing. 

 

2.	Content version/revision control

Experience: This function works well on Jackrabbit v1.3. The main problem is that all revision
(except base revision) of node are lost when export/import data from one repository to another
repository. I am discussing this issue because it concerns the repository backup.

 

I just found in JackRabbit v1.3, there is no way to backup repository using DB as persistence
manager. I mean that there is no way to re-index based on data on DB. The following is my
case:

 

In one repository server, the index (in file system) is corrupt which causes all search failure.
However, all data (in DB) is still alive, where you can iterate all of them. After clean the
whole repository file system (most of them are index information), Jackrabbit can not correctly
re-build index based on the data on DB. If it happens on production repository, it means:
"My God, I am going to be fired". As I know, Jackrabbit v1.1 can successfully re-index (creating
totally new repository index (file system) based on DB data).

 

As the alternative solution to backup repository, I try to export/import all nodes from repository
to another repository using JCR Export API (exportSystemView). The good news is that JackRabbot
v1.3 successfully builds index (the whole file system) during the importing process; the bad
news is that it lost all revision of all versioning nodes. Can you image how frustrate I am
when I realize there is no way to backup repository based on DB data?

 

I just got the answer for the re-index issue for Jackrabbit v1.3: You CAN NOT delete all file
system. Only delete all indexes but keep the other folders. Jackrabbit can re-index successfully
when it starts up. 

 

Question 2: 

How can developer correctly use Jackrabbit (JCR) as their repository solution?

 

The expert of jackrabbit may see that I use object to describe node and you may think it is
not the pattern you are using Jackrabbit. So the question is raised as "Which is the best
practices (pattern) to use Jackrabbit (JCR) as repository solution."

 

>From this community, I see a lot of developers use Jackrabbit by fetching contents by
path. It means that they do not need treat node as object, instead, they put content on repository
as asset, which can be easily and effectively retrieved by a given path. This pattern exactly
meets the truth of "The simplicity is the best".

 

My use of Jackrabbit is based on the business requirement, which need to navigate most of
nodes and reference nodes, check child nodes and properties to find the proper content by
a couple of business rules. I would like to say that all performance issues are raised by
nodes iteration process. Even more, I have created generic classes using java reflect package
for bi-directory mapping between nodes and objects. For performance improvement, the mapping
supports generic child nodes lazy loading. However, it seems all these jobs do not solve the
performance problem although they sound pretty "professional".  You may ask me: if you have
such business requirement, why not go to DB and build the full relationship for your business
model? J2EE developers all know how powerful java-db world is: the mature ORM tool (e.g. Hibernate),
transaction management, batch data fetching, performance tuning and so on. However, my question
is: "Is there any good pattern in current jackrabbit to effectively handle data fetching with
week relationship?" 

 

Now it is time to say some words to the jackrabbit developers and contributors what I really
want to say for the whole community:

 

My begs:

Guide, document and sample code is the king for any open source. How frustrating for Jackrabbit
developers find the incorrect pattern is applied by users on their projects. On the other
hand, how frustrating for JackRabbit users can not find the good pattern to follow, which
can save their bunch of time. From product point of view, the search by XPath or XQuery or
SQL is not foundational issue. The foundational issue is one effective search means covers
most of important requirements from real world and the document can be found in jackrabbit
web site.

 

 

I do believe Jackrabbit is qualified project and I really hope all "best features" are documented,
demoed and used by the whole community.

 

Thanks 

 

Bruce

 

 

 

  

 

 

 

 

 

 


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