Datalab server implementation of VOSpace 2.0 specification

Our instantiation of the specification is done in a Java REST API over a tomcat server.

The VOSpace code uses a mysql database, usually running in the same machine as the Tomcat server does. The code connects to it via unix socket. (Typically when connecting to a database if the host is localhost as opposed to an ip address even if the identity 127.0.0.1, the client will try to use the unix socket file, which is much faster.) Archival data storage and accounts folders are mounted over NFS.

Also access to the VOSpace instance happens over proxy from the main web server.

We use the Apache Wink RESTful framework to facilitate some of the work that normally goes into the WEB-INF/web.xml file. The Apache Wink project has been retired since 2017. The code is very stable but if at some point it creates a problem we can always move the REST bindings to the web.xml file.

With Wink, instead of defining each of the REST APIs as entries in the web.xml, we use a text file: WEB-INF/application that lists all the available resources that implement the REST bindings.

E.g.\

Notice the NodeMessageBodyWriter and NodeMessageBodyReader java classes at the end of the list. These are used to serialize/deserialize the xml load to and from java objects. Something the WINK framework does automatically behind the scenes.

Note: The new VOSpace specification v. 2.1 is very similar to v. 2.0 except that it includes some improvements to the protocols and transfers but for the most part it is the same.

The VOSpace database is pretty simple and follows the data model, with only a handful of tables.

Main tables:\

• nodes
  Contains an entry for every file type on disk, which are referred as nodes. The most relevant attributes in a nodes entry are:

  • URI/identifier: A unique identifier for the node.
  • owner: owner of the node
  • location: where the node is actually on disk
  • depth: The subdirectory level

• properties
  Contains an entry for every file type/node on disk. The relation between the properties and nodes table are 1:1
  The attributes in this table are meta information on the node, such as read/write permissions, ctime, mtime, etc

• addl_props
  Additional metadata information.

• capabilities
  Matches a node with a capability. A capability is another service interface that can handle the node or its contents in a particular way. For instance, it might be a cutout service that knows how to cut images in a particular way.

• transfers and results
  When a job is requested these two tables will keep the transfer uri and state.

We've performed the following improvements on the code, see git commits:

• 34867f6a,821a5394,ccea0c77,529d7c5b
  Logging
• dfc8781a,dfc8781a
  SQL improvements
• 37733d4d
  Ignoring MD5 attribute
• 5074907c
  Duplicate copying effort bug
• 7df247d7,d265ddf6,ef81b369,0e8bbc76,b25a4b7d1be
  XML serialization performance improvement
• d59eb094
  Improving transfer DB and SQL inner workings.

There still a few more things it can be done:

• In the nodes & properties table:
  • create a column with a shorter unique identifier:
    i.e 8 byte numeric key and use that column to:
    • join against the properties table and other tables instead of using the very long identifier column.
    • ability to set the parent on nodes. I will make easier/faster to find a node's children.
  • shorten the identifier column and make its index more compact by removing the vospace + owner prefix, 30+ characters of redundant information.
• Make the properties table more compact by using integers, instead of characters, to describe the node permissions.
• Having a background job that calculates and sets each node/file MD5/SHA checksum

• java 1.8
• tomcat 5.5 and above

Under the ./java directory there is a build.xml ant file.

To list available ant commands/targets do:

ant -p
Buildfile: ./vospace/java/build.xml

        Ant build file for VOSpace 2.0

Main targets:

 clean    clean up
 compile  compile the source
 deploy   deploy to Tomcat webapps directory
 dist     generate the distribution
Default target: dist

by running ant or ant dist a vospace-2.0.war will be created. Then simply copy/drop that file into your tomcat webapps directory and restart tomcat server.

curl -v 'http://vostest.datalab.noirlab.edu:8080/vospace-2.0/vospace/nodes/ls_dr8?detail=min&uri=vos://datalab.noao!vospace/ls_dr8/south/tractor/275'

returns:

   <node xmlns="http://www.ivoa.net/xml/VOSpace/v2.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="vos:ContainerNode"
         uri="vos://datalab.noao!vospace/ls_dr8"
         busy="false">
         <properties />
         <nodes />
   </node>

See README file in the test directory for more information about how to run these tests.