20 Oct
2010
20 Oct
'10
11:33 a.m.
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 ?
If streams are available for the databases that support it, which ones
support it ?
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.
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.
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 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
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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