21 Oct
2010
21 Oct
'10
9:48 p.m.
On Wed, Oct 20, 2010 at 11:33, Ludovic Dubost <ludovic(a)xwiki.com> wrote:
Hi,
We do want the availability of file attachment storage (Sergiu has done an
implementation during the summer hackathon), but as Guillaume said it should
be to the choice of the administrator.
Now concerning database storage, about Hibernate, does it means streams are
not available at all in Hibernate or does it mean they don't always work ?
It works but does not really stream using MySQL. This is not a Hibernate
issue, but the way MySQL connector works.
If streams are available for the databases that
support it, which ones
support it ?
Oracle does it well.
Concerning your proposal, it's interesting as
indeed if we use streams for
everything else, we do get rid of the memory consuption issue for
attachments.
Now I have a few concerns:
- complexity and management of the data. What happens if we have a
corrupted DB and one of the chunks fails to save. We might end up with
invalid content.
- we also have to solve other large items (like attachment history or
recycle bin of attachments)
On a side note concerning the max_allowed_packet issue in MySQL, I was able
to change that value at runtime (from the mysql console). If this also works
using a remote connection, maybe we could hack and force a big value at
runtime.
This would be really great because the max_allowed_packet is killing us.
XWiki does not report it well in many cases and almost no customers reads
the documentation and sets the value properly. We also have seen in many
cases, where the database is shared with other applications, and there is
little access to the database configuration and to the ability of restart.
To make it short, the max_allowed_packet issue is a major issue when
operating XWiki.
For sure, but there is also issue with Term of Usages for dedicated MySQL
hosting provide by popular providers, especially when the database size is
not limited. Storing attachments in the database may be assimilated to using
the database as a file system, and such usage is sometimes disallowed.
Before we go into large fixes for that problem, could we maybe at least
check that we report errors properly (on a 2.0.5 we were not for sure at
least for attachment saving failure). We should also make sure we can always
delete even when we cannot read the data in memory. This is also not the
case when we cannot read the data because it's too big or because one of the
tables does not have any data.
I strongly agree.
I am +1 for alternative with appropriate configuration to have them
disabled.
Denis
Ludovic
Le 18/10/10 19:55, Caleb James DeLisle a écrit :
I talked with the Hibernate people about using streams and was told that
--
Denis Gervalle
SOFTEC sa - CEO
eGuilde sarl - CTO
it is not supported by all
databases.
As an alternative to the proposal below I would like to propose a
filesystem based storage mechanism.
The main advantage of using the database to store everything is that
administrators need only use
mysql_dump and they have their entire wiki backed up.
If we are to abandon that requirement, we can have much faster attachment
storage by using the
filesystem. For this, I propose BinaryStore interface remains the same but
com.xpn.xwiki.doc.BinaryObject would contain:
void addContent(InputStream content)
OutputStream addContent()
void clear()
InputStream getContent()
void getContent(OutputStream writeTo)
clear() would clear the underlying file whereas addContent would always
append to it.
The added column would look like this:
<class name="com.xpn.xwiki.store.doc.FilesystemBinaryObject"
table="filesystembinaryobject">
<id name="id" column="id">
<generator class="native" />
</id>
<property name="fileURI" type="string">
<column name="fileuri" length="255"
not-null="true"/>
</property>
</class>
This would as with the original proposal be useful for not only storing
attachments but attachment
history, deleted attachments and even document history or deleted
documents.
WDYT?
Caleb
On 10/15/2010 04:21 PM, Caleb James DeLisle wrote:
--
Ludovic Dubost
Blog: http://blog.ludovic.org/
XWiki: http://www.xwiki.com
Skype: ldubost GTalk: ldubost
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Because the storage of large attachments is
limited by database
constraints and the fact that the
JDBC does not allow us to stream content out of the database, I propose
we add a new database table
binarychunk.
The mapping will read as follows:
<class
name="com.xpn.xwiki.store.hibernate.HibernateBinaryStore$BinaryChunk"
table="binarychunk">
<composite-id unsaved-value="undefined">
<key-property name="id" column="id"
type="integer" />
<key-property name="chunkNumber" column="chunknumber"
type="integer" />
</composite-id>
<property name="content" type="binary">
<column name="content" length="983040"
not-null="true"/>
</property>
</class>
Notice the maximum length (983040 bytes) is a number which is divisible
by many common buffer sizes
and is slightly less than the default max_packet_size in mysql which
means that using the
xwikibinary table, we could store attachments of arbitrary size without
hitting mysql default limits.
com.xpn.xwiki.store.BinaryStore will contain:
@param toLoad a binary object with an id number set, will be loaded.
void loadObject(BinaryObject toLoad)
@param toStore a binary object, if no id is present then it will be given
one upon successful
store, if id is present then that id number will be used.
void storeObject(BinaryObject toStore)
This will be implemented by:
com.xpn.xwiki.store.hibernate.HibernateBinaryStore
com.xpn.xwiki.doc.BinaryObject will contain:
void setContent(InputStream content)
OutputStream setContent()
InputStream getContent()
void getContent(OutputStream writeTo)
Note: The get function and set functions will be duplicated with input or
output streams to maximize
ease of use.
This will be implemented by com.xpn.xwiki.doc.TempFileBinaryObject which
will store the binary
content in a temporary FileItem (see Apache commons fileupload).
+ This will be able to provide a back end for not only attachment
content, but for attachment
archive and document archive if it is so desired.
+ I have no intent of exposing it as public API at the moment.
WDYT?
Caleb
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