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From: Apache Wiki <wikidiffs@apache.org>
To: Apache Wiki <wikidiffs@apache.org>
Date: Mon, 07 Dec 2009 08:43:02 -0000
Message-ID: <20091207084302.25164.83800@eos.apache.org>
Subject: 
 =?utf-8?q?=5BJackrabbit_Wiki=5D_Update_of_=22PersistenceManagerFAQ=22_by_?=
 =?utf-8?q?ThomasMueller?=

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Jackrabbit Wiki" fo=
r change notification.

The "PersistenceManagerFAQ" page has been changed by ThomasMueller.
http://wiki.apache.org/jackrabbit/PersistenceManagerFAQ?action=3Ddiff&rev1=
=3D33&rev2=3D34

--------------------------------------------------

- =3D Persistence Manager (PM) FAQ =3D
+ =3D=3D Persistence Manager =3D=3D
  =

+ <<TableOfContents>>
+ =

+ =3D=3D Overview =3D=3D
+ =

- =3D=3D What is a Persistence Manager (PM)? =3D=3D
+ =3D=3D=3D What Is a Persistence Manager (PM)? =3D=3D=3D
  The PM is an *internal* Jackrabbit component that handles the persistent =
storage of content nodes and properties. Property values are also stored in=
 the persistence manager, with the exception of large binary values (those =
are usually kept in the DataStore).
  =

  Each workspace of a Jackrabbit content repository uses a separate persist=
ence manager to store the content in that workspace. Also the Jackrabbit ve=
rsion handler uses a separate persistence manager. =

@@ -26, +30 @@

  The PM sits at the very bottom layer in jackrabbits system architecture. =

  Reliability, integrity and performance of the PM are *crucial* to the ove=
rall stability & performance of the repository. If e.g. the data that a PM =
is based upon is allowed to change through external means the integrity of =
the repository would be at risk (think of referential integrity / node refe=
rences e.g.).
  =

- =3D=3D=3D=3D Which Persistence Manager is the fastest? =3D=3D=3D=3D
+ =3D=3D=3D Which Persistence Manager Is the Fastest? =3D=3D=3D
  The bundle persistence managers are usually the fastest. Bundle persisten=
ce managers store each node together with all the properties as one unit. L=
arge binary properties are stored to the BLOBStore by default (or DataStore=
 if configured). Setting the minimum blob size for bundle persistence manag=
ers very high decreases the performance.
  =

  Storing the data in the file system does not require a database. Dependin=
g on the file system and database, database persistence managers are someti=
mes slower and sometimes faster than the Bundle``Fs``Persistence``Manager. =
When using a database, please note that embedded Java databases do not have=
 network overhead.
  =

- =3D=3D=3D=3D Consistency / Atomicy =3D=3D=3D=3D
+ =3D=3D=3D Consistency / Atomicy =3D=3D=3D
  =

  The database persistence managers are atomic if the database is atomic.
  =

  The current file based persistence managers are not always atomic. They d=
o support transactions in Jackrabbit, the exception is after a crash: When =
the process is stopped while a transaction is being written to disk (power =
failure, process killed, Runtime.halt() called, VM crash), some data of a t=
ransaction may be committed and some not. Theoretically, some nodes may be =
corrupt (depending how and when the system crashed). The algorithms used ar=
e minimizing this risk, for example the parent node is written last so in m=
ost cases there is no problem even after a crash. =

  =

- =3D=3D=3D=3D What's the PM responsibility? =3D=3D=3D=3D
+ =3D=3D=3D What's the PM Responsibility? =3D=3D=3D
  The PM interface was never intended as being a general SPI that you could=
 implement in order to integrate external datasources with proprietary form=
ats (e.g. a customers database). the reason why we abstracted the PM interf=
ace was to leave room for future performance optimizations that  would not =
affect the rest of the implementation (e.g. by storing the raw data in a b-=
tree based database instead of individual file).
  =

- =3D=3D=3D=3D How smart should a PM be? =3D=3D=3D=3D
+ =3D=3D=3D How Smart Should a PM Be? =3D=3D=3D
  A PM should not be 'intelligent'. It should not 'interpret' the data. The=
 only thing a PM should care about is to efficiently, consistently and reli=
ably store and read the data encapsulated in the passed nodeState & propert=
yState objects. Though it might be feasible to write a custom persistence m=
anager to represent existing legacy data in a level-1 (read-only) repositor=
y, I don't think the same is possible for a level-2 repository.  At a minim=
um, it certainly would not be recommended.
  =

- =3D=3D=3D=3D File System (FS) =3D=3D=3D=3D
+ =3D=3D=3D File System (FS) =3D=3D=3D
  =

  Jackrabbit uses the org.apache.jackrabbit.core.fs.FileSystem interface as=
 a file system abstraction. Although this interface does not cover all dire=
ct file system use of Jackrabbit, it still allows for flexibility in select=
ing where and how to store various parts of the repository. For example, be=
cause it is possible with Jackrabbit to configure separate file systems for=
 different system components (e.g., global repository state, workspaces, se=
arch indexes, versioning, etc), it might make sense to store the search ind=
exes on a fast disk and the archived node versions on a slower disk. =

  =

- =3D=3D=3D=3D What combination of FS and PM is the best choice? =3D=3D=3D=
=3D
+ =3D=3D=3D What Combination of FS and PM is the Best Choice? =3D=3D=3D
  It depends on your priorities. If you want to store your data in a RDBMS,=
 use Bundle``Db``Persistence``Manager in conjunction with either a Local``F=
ile``System or Db``File``System. If you want to store your data in an more =
readily accessible format (just in case ;), you might want to try an XML``P=
ersistence``Manager paired with a Local``File``System.
  =

  =3D=3D Available Implementations =3D=3D
  =

- =3D=3D=3D=3D Bundle Database PM =3D=3D=3D=3D
+ =3D=3D=3D Bundle Database PM =3D=3D=3D
   * Status: mature (the default persistence manager)
   * Depending on the database, one of the following:
     * org.apache.jackrabbit.core.persistence.bundle.Derby``Persistence``Ma=
nager (Apache Derby; Java)
@@ -69, +73 @@

   * The tables are automatically created. To create them manually, see [[M=
anuallyCreatingDatabaseTables]].
   * [[http://jackrabbit.apache.org/api/1.5/org/apache/jackrabbit/core/pers=
istence/bundle/BundleDbPersistenceManager.html|BundleDbPersistenceManager]]
  =

- =3D=3D=3D=3D Bundle File-System PM =3D=3D=3D=3D
+ =3D=3D=3D Bundle File-System PM =3D=3D=3D
   * Status: mature
   * If the JVM process is killed the repository might turn inconsistent
   * Not meant to be used in production environments (except for read-only =
uses)
@@ -77, +81 @@

   * Very fast if used with DataStore or BLOBStore
   * [[http://jackrabbit.apache.org/api/1.4/org/apache/jackrabbit/core/pers=
istence/bundle/BundleFsPersistenceManager.html|BundleFsPersistenceManager]]
  =

- =3D=3D=3D=3D In-Memory PM =3D=3D=3D=3D
+ =3D=3D=3D In-Memory PM =3D=3D=3D
   * Status: mature
   * All data is lost as soon as the repository is closed
   * org.apache.jackrabbit.core.persistence.mem.In``Mem``Persistence``Manag=
er
@@ -87, +91 @@

   * Very fast
   * [[http://jackrabbit.apache.org/api/1.4/org/apache/jackrabbit/core/pers=
istence/mem/InMemPersistenceManager.html|InMemPersistenceManager]]
  =

- =3D=3D=3D=3D Simple Database PM =3D=3D=3D=3D
+ =3D=3D=3D Simple Database PM =3D=3D=3D
   * Status: mature
   * Subclasses of org.apache.jackrabbit.core.persistence.db.Simple``Db``Pe=
rsistence``Manager
   * JDBC based; zero-deployment: schema is automatically created
@@ -95, +99 @@

   * Fast
   * [[http://jackrabbit.apache.org/api/1.4/org/apache/jackrabbit/core/pers=
istence/db/SimpleDbPersistenceManager.html|SimpleDbPersistenceManager]]
  =

- =3D=3D=3D=3D ObjectPersistenceManager =3D=3D=3D=3D
+ =3D=3D=3D ObjectPersistenceManager =3D=3D=3D
   * Status: obsolete, mature
   * If the JVM process is killed the repository might turn inconsistent
   * Not meant to be used in production environments =

   * Persists data in an abstract File``System using a simple binary serial=
ization format
  =

- =3D=3D=3D=3D XMLPersistenceManager =3D=3D=3D=3D
+ =3D=3D=3D XMLPersistenceManager =3D=3D=3D
   * Status: obsolete, mature
   * If the JVM process is killed the repository might turn inconsistent
   * Persists data in an abstract File``System using XML serialization form=
at
  =

- =3D=3D=3D=3D ORMPersistenceManager =3D=3D=3D=3D
+ =3D=3D=3D ORMPersistenceManager =3D=3D=3D
   * Status: obsolete, experimental & unfinished, still being maintained?
   * Referential integrity is possible, but not implemented
   * Not so easy to configure.
  =

- =3D=3D=3D=3D LocalFileSystem: =3D=3D=3D=3D
+ =3D=3D=3D LocalFileSystem: =3D=3D=3D
   * Status: mature
   * Slow on window boxes
  =

- =3D=3D=3D=3D MemoryFileSystem: =3D=3D=3D=3D
+ =3D=3D=3D MemoryFileSystem: =3D=3D=3D
   * Status: mature
   * All data is lost as soon as the repository is closed
   * For testing and small (read-only) workspaces =

   * Keeps all content in memory
   * Very fast
  =

- =3D=3D=3D=3D DbFileSystem: =3D=3D=3D=3D
+ =3D=3D=3D DbFileSystem: =3D=3D=3D
   * Status: mature
   * Atomic
   * Meant to be used in combination with a Database Persistence Manager as=
 repository & workspace file system=20