DBpedia Snapshot (Virtuoso PAGO) for Microsoft Azure Cloud

Content Index

Introduction

What is this offering about?

Cloud Hosted Pay-As-You-Go (PAGO) edition of a preconfigured Virtuoso instance that includes a pre-loaded an optimized DBpedia 2021-12 Snapshot Edition Knowledge Graph.

Who is this for?

Any architect, systems integrator, or developer that seeks an application- or service-specific instance of DBpedia for high-performance and scalable interaction with its powerful Knowledge Graph.

What need is addressed by this offering?

Access to the DBpedia Knowledge Graph without the constraints enforced by the “Fair Use” policy of the general public instance.

Prerequisites

Deployment via Azure Marketplace Offer Page

  1. From the Azure Marketplace search for the keyword DBpedia to locate the available DBpedia offering and select the PAGO offer:




  2. Click on the GET IT NOW button to start the subscription and deployment of the DBpedia PAGO offer:




  3. Select Continue to start the deployment process in the Azure Portal.




  4. Select the Create button to start the VM configuration manually or select the Start with a pre-set configuration to start the a pre set configuration.




  5. From the Basics tab choose the Resource group , which can be an existing or new group; set the Virtual machine name to call the deployment; set the Region to deploy from; for SSH public key source` choose to either use and existing or public key to be used.






  6. From the Disks tab, typically the defaults can be used, or additional disks can be added as required.




  7. From the Networking tab, typically the defaults can be used.




  8. For the remaining Management, Advanced and Tags tabs the defaults can also be used and the Create + Review button selected to validate the deployment




  9. Once the Validation passed message occurs, click on the Create button to start the deployment




  10. The Your deployment is complete message is display once successfully completed.




  11. Click on the Goto resource button to load the Overview page of the successfully deployed VM, from which the Public IP address can be copied for use to access the VM via ssh and http.




DBpedia Snapshot (Virtuoso PAGO) Database Interaction via Web Interface

Once online, your DBpedia Snapshot instance will be ready for use from —

  • Basic Linked Data Exploration Page — an obvious starting point
http://{azure-cloud-vm-dns-name-or-ip-address}/resource/DBpedia
  • Faceted Browsing Endpoint
http://{azure-cloud-vm-dns-name-or-ip-address}/fct
  • Advanced Faceted Browsing Page
http://{azure-cloud-vm-dns-name-or-ip-address}/describe/?uri=http://dbpedia.org/resource/DBpedia
  • SPARQL Query Service Endpoint
http://{azure-cloud-vm-dns-name-or-ip-address}/sparql
  • Virtuoso Instance Administration Page (Virtuoso Conductor)
http://{azure-cloud-vm-dns-name-or-ip-address}/conductor

Administering the Virtuoso Instance via SSH

  1. Make a ssh connection to the VM using the public key ( pem-file ) and username ( ubuntu by default) chosen when creating the deployment, and the Public IP address from the previous section as follows:
    ssh -i {pem-file} azureuser@{Public IP address}
  1. Once connected it is strongly recommended to update the VM to get the latest operating system and Virtuoso updates with the command:
    sudo apt-get upgrade
  1. Check the Virtuoso server is automatically started post deployment with the command:
    sudo service virtuoso status
  1. The following commands can be used to Administer the Virtuoso server:
  • Start the Virtuoso Server:
    sudo service virtuoso start
  • Stop the Virtuoso Server:
   sudo service virtuoso stop
  • Restart the Virtuoso Server:
    sudo service virtuoso restart
  • Check status of Virtuoso Server:
    sudo service virtuoso status
  1. Determine the random password set for the dba user with the command:
    sudo cat /opt/virtuoso/database/.initial-password
  1. A SQL connection can then be made Virtuoso with the isql command line tool with the command on port 1111 :
    isql 1111
  1. Typical output for running these steps are:
$ ssh -i certificates/virtuoso.pem ubuntu@54.221.25.206
The authenticity of host '54.221.25.206 (54.221.25.206)' can't be established.
ECDSA key fingerprint is SHA256:QGsOFcQoa4x5DBavtdHWDQUUQtBdHJ/OkizKep8UOcM.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '54.221.25.206' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 18.04.5 LTS (GNU/Linux 5.4.0-1025-aws x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Fri Jan 29 12:41:03 UTC 2021

  System load:  0.0                Processes:           104
  Usage of /:   2.0% of 116.27GB   Users logged in:     0
  Memory usage: 4%                 IP address for eth0: 10.0.0.214
  Swap usage:   0%


 * Canonical Livepatch is available for installation.
   - Reduce system reboots and improve kernel security. Activate at:
     https://ubuntu.com/livepatch

9 packages can be updated.
0 updates are security updates.


Last login: Tue Sep 22 19:26:19 2020 from 108.26.205.225
ubuntu@ip-10-0-0-214:~$ cd /opt/virtuoso/database
ubuntu@ip-10-0-0-214:/opt/virtuoso/database$ sudo bash
root@ip-10-0-0-214:/opt/virtuoso/database# cat .initial-password 
i-0343ad51fe5e4f196
root@ip-10-0-0-214:/opt/virtuoso/database# service virtuoso status
● virtuoso.service - OpenLink Virtuoso Database
   Loaded: loaded (/lib/systemd/system/virtuoso.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2021-01-29 12:04:31 UTC; 38min ago
  Process: 878 ExecStart=/opt/virtuoso/bin/virtuoso-start.sh $VIRTUOSO_DB_NAMES (code=exited, status=0/SUC
 Main PID: 1170 (virtuoso)
    Tasks: 15 (limit: 4915)
   CGroup: /system.slice/virtuoso.service
           └─1170 ./virtuoso

Jan 29 12:04:25 ip-10-0-0-214 systemd[1]: Starting OpenLink Virtuoso Database...
Jan 29 12:04:26 ip-10-0-0-214 virtuoso-start.sh[878]: Starting Virtuoso instance in [database]
Jan 29 12:04:26 ip-10-0-0-214 virtuoso-start.sh[878]:   - Starting the database
Jan 29 12:04:31 ip-10-0-0-214 systemd[1]: Started OpenLink Virtuoso Database.
root@ip-10-0-0-214:/opt/virtuoso/database# /opt/virtuoso/bin/isql 1111
OpenLink Virtuoso Interactive SQL (Virtuoso)
Version 08.03.3319 as of Sep  1 2020
Type HELP; for help and EXIT; to exit.

Enter password for dba :
Connected to OpenLink Virtuoso
Driver: 08.03.3319 OpenLink Virtuoso ODBC Driver
SQL> status('');
REPORT
VARCHAR
_______________________________________________________________________________

OpenLink Virtuoso VDB Server
Version 08.03.3319-pthreads for Linux as of Sep  1 2020 
Started on: 2021-01-29 12:45 GMT+0
CPU: 0.05% RSS: 148MB PF: 0
 
Database Status:
  File size 67108864, 8192 pages, 5733 free.
  20000 buffers, 1115 used, 85 dirty 0 wired down, repl age 0 0 w. io 0 w/crsr.
  Disk Usage: 1074 reads avg 0 msec, 0% r 0% w last  23 s, 138 writes flush          0 MB/s,
    34 read ahead, batch = 17.  Autocompact 0 in 0 out, 0% saved.
Gate:  166 2nd in reads, 0 gate write waits, 0 in while read 0 busy scrap. 
Log = virtuoso.trx, 8325 bytes
VDB: 0 exec 0 fetch 0 transact 0 error
2309 pages have been changed since last backup (in checkpoint state)
Current backup timestamp: 0x0000-0x00-0x00
Last backup date: unknown
Clients: 1 connects, max 1 concurrent
RPC: 6 calls, 1 pending, 1 max until now, 0 queued, 0 burst reads (0%), 0 second 0M large, 10M max
Checkpoint Remap 38 pages, 0 mapped back. 0 s atomic time.
    DB master 8192 total 5733 free 38 remap 1 mapped back
   temp  256 total 251 free
 
Lock Status: 0 deadlocks of which 0 2r1w, 0 waits,
   Currently 1 threads running 0 threads waiting 0 threads in vdb.

24 Rows. -- 2 msec.
SQL> 

Performance Tuning

There are a range of Azure VM instance types with different system memory and CPU combinations. Collectively, the factors above affect the performance of your Virtuoso instance. Thus, use Azure VM Instance Type s with more memory and CPU cores for best performance.

Note: This VM is configured to use minimal system memory. For the instance type chosen, the NumberOfBuffer and MaxDirtyBuffers parameters in the /opt/virtuoso/database/virtuoso.ini configuration file should be increased to match the available memory, as detailed in the Virtuoso Performance Tuning Guide, for example –

VM Instance Type System RAM Number Of Buffers Max Dirty Buffers
B2MS 8 GB 680000 500000
B4MS 15 GB 1360000 1000000
M32S 32 GB 2720000 2000000
M64LS 64 GB 5450000 4000000

– and the Virtuoso server restarted as detailed above.

Extrapolate the NumberOfBuffer and MaxDirtyBuffers parameters accordingly for different sized VMs.

Troubleshooting

If the Virtuoso server fails to start:

  • Run the command sudo service virtuoso status to see if the Virtuoso server is running
  • Check the /opt/virtuoso/database/virtuoso.log file to see why the server might have failed to start
  • Ensure there file /opt/virtuoso/database/virtuoso.lck does not exist before starting the server
  • Attempt to start the Virtuoso server with the command sudo service virtuoso start
  • Run the command sudo service virtuoso status again to see if the Virtuoso server is running
  • If it is now running attempt a connect via the SQL or HTTP interfaces are detailed above

Additional Information Sources