Configuring Virtuoso for Scale
Table of Contents
Background
OpenLink Virtuoso is an engine of many features. It incorporates a database engine, Web server, RDF quad-store, SPARQL processor, and the OpenLink Data Spaces (ODS) suite of applications for bookmarks, briefcase, wiki, webmail, etc.
Naturally, each of these features has its dependencies and consequences for resource usage, be that in-memory or on disk.
Here we present an overview of 3 possible configurations for Virtuoso.
For comparison, we use Virtuoso Open-Source Edition (VOS) compiled on Debian GNU/Linux ("Testing" distribution).
Structure of a Virtuoso Installation
A typical Virtuoso installation comprises the following files/areas:
Directory | Description | Files | Size |
---|---|---|---|
/usr/bin/ |
Vital operating binaries for server and command-line client | virtuoso-t isql-v isql-vw |
9.2 M |
/usr/share/virtuoso/vad/ |
ODS and other packages (rdf_mappers/sponger, tutorial, demo, isparql, etc.) | rdf_mappers_dav.vad doc_dav.vad |
131 M |
/usr/lib/ |
client drivers for ODBC & JDBC | jdbc-2.0/virtjdbc*.jar virtodbc*.so |
12 M |
/usr/lib/virtuoso/hosting/ |
Runtime loadable plugins for hosting and wiki markup | wikiv.so mediawiki.so creolewiki.so |
3.6 M |
/var/lib/virtuoso/vsp/ |
Splash-page for top-level web interface | vsp/ vsmx/ images/ frames/ css/ index.html etc. |
1.5 M |
/usr/share/doc/virtuoso-opensource/ |
Misc README data for OS platform | README.Debian README.CVS.gz etc. |
128 K |
/usr/lib/jena/ |
Java class modules for using Virtuoso from Jena | virt_jena.jar |
56 K |
/usr/lib/sesame/ |
Java class modules for using Virtuoso from Sesame | virt_sesame2.jar |
56 K |
/var/lib/virtuoso/db |
Default database directory | virtuoso.ini virtuoso.db |
12 M |
Operation
When the server is run against a given .ini file, it looks for a database at the name and location specified in that file. If none is found, the server will create an empty database with minimal system schema.
If it finds an appropriate directory containing *.vad files (set in the virtuoso.ini file during `make install'), Virtuoso will install the Conductor package by default.
From there on, the Virtuoso administrator is expected to use the Conductor, <http://localhost:8890/conductor/>, to install further packages such as the ODS application suite, etc.
After a checkpoint, a virtuoso.db file forms a portable unit encapsulating the entirety of a database instance, and can be moved between servers, so you can implement custom applications and schemas using the client interfaces (SQL/ODBC/JDBC) and avoid installing any of the packages, even the Conductor, should you so desire.
Configuration Options
The following parameters in a virtuoso.ini file defining a Virtuoso instance control the resource consumption and performance:
[Database] |
|||
DatabaseFile |
virtuoso.db |
Filename of database file | docs |
FileExtend |
200 |
The amount of 8K-sized pages by which the database file automatically grows when the current file is not large enough. | docs |
MaxCheckpointRemap |
2000 |
Controls how many pages may be stored other than their logical page during checkpoints | docs |
Striping |
0 |
Enables the database file-striping mechanism | docs |
[Parameters] |
|||
ServerThreads |
20 |
maximum number of threads (SQL+HTTP) used in the server - should be close to the number of concurrent connections | docs |
CheckpointInterval |
60 |
interval (minutes) at which Virtuoso will automatically make a database checkpoint | docs |
NumberOfBuffers |
2000 |
controls the amount of RAM (8K pages) used by Virtuoso to cache database files | docs |
MaxDirtyBuffers |
1200 |
The maximum number of modified buffers to store before writing | |
MaxStaticCursorRows |
5000 |
the maximum number of rows returned by a static cursor | docs |
FreeTextBatchSize |
100000 |
the amount of text data processed in one batch of the free-text index during batch reindexing | docs |
[HTTPServer] |
|||
ServerThreads |
10 |
Maximum concurrent HTTP sessions; must be less than the overall database ServerThreads | docs |
MaxKeepAlives |
10 |
A maximum number of HTTP sockets with KeepAlive connections | docs |
KeepAliveTimeout |
10 |
Timeout (s) before an idle HTTP connection is closed | docs |
HTTPThreadSize |
280000 |
Stack-size of an HTTP thread for handling connection and processing | docs |
[Striping] |
|||
Segment1 |
100M, db-seg1-1.db, db-seg1-2.db |
Segment-specification for disk-striping | docs |
Segment2 |
100M, db-seg2-1.db |
||
[SPARQL] |
|||
ResultSetMaxRows |
100000 |
Maximum number of rows in a SPARQL resultset | docs |
[Plugins] |
|||
LoadPath |
/usr/lib/virtuoso/hosting |
Directory in which to search for plugins | docs |
Load1 |
plain, wikiv |
Main ODS-Wiki markup parser | |
Load2 |
plain, mediawiki |
Auxilliary MediaWiki markup parser module for ODS-Wiki | |
Load3 |
plain, creolewiki |
Auxilliary Creole wiki markup parser module for ODS-Wiki | |
Load4 |
plain, im |
ImageMagick plugin used by ODS-Gallery | |
Load5 |
plain, wbxml2 |
WbXML plugin used by the SyncML package | |
Load6 |
plain, hslookup |
Required for some Sponger Cartridge operations | |
Load7 |
Hosting, hosting_php.so |
Module for hosting PHP scripts within Virtuoso | |
;Load8 |
Hosting,hosting_perl.so |
Module for hosting Perl scripts within Virtuoso (unsupported at present) | |
;Load9 |
Hosting,hosting_python.so |
Module for hosting Python scripts within Virtuoso (unsupported at present) | |
;Load10 |
Hosting,hosting_ruby.so |
Module for hosting Ruby scripts within Virtuoso (unsupported at present) | |
;Load11 |
msdtc,msdtc_sample |
For Microsoft XA transaction support |
Notes:
- Striping is an obvious way to control the amount of disk-space used; by default, striping is off (0) so the [Striping] section does not come into play.
- The checkpoint-interval setting is simply the amount of time for which a temporary database will grow before being checkpointed into the main virtuoso.db file, so a choice is scenario-dependent; for a given incoming transaction rate, a short interval will give frequent smaller checkpoints while specifying a longer interval will make fewer, slower, checkpoints.
- The numbers of threads in the database engine as a whole and specifically allocated to the HTTP server will control performance, and each thread will cost a given amount of memory also.
- Naturally you can disable any or all unused plugins for further reduce the memory footprint; for example, if not running ODS-Wiki, you can remove the wikiv, mediawiki and creolewiki plugins.
We have a documentation page on tuning Virtuoso for RDF usage.
Analysis
Virtuoso provides the status()
command, which
may be executed through the SQL interface (e.g.,
isql-v(1)).
The resultset from this command is documented here, but we highlight
specifically consideration of the
NumberOfBuffers
parameter; from
status()
output you will see how many buffers
the server is actually using so you can tailor the allocated
number accordingly.
Default
By default, the Debian virtuoso-opensource package enables all possible hosting options except Mono.
package .deb | 58 M |
server binary, /usr/bin/virtuoso-t | 8.3 M |
default database with Conductor installed | 37 M |
Virtual memory allocation | 354 M |
Resident memory used | 125 M |
Embedded / Minimal
The minimum that is required to run Virtuoso is the server
executable (virtuoso-t
, or in commercial
edition, virtuoso-iodbc-t
) compiled with as few
options as possible, and the virtuoso.ini
file.
From there, the first time the server is run against the
virtuoso.ini
, it will create the empty database
(virtuoso.db
) with minimal schema.
The most important parameter to consider when optimizing
for size is NumberOfBuffers
.
By applying a few changes to virtuoso.ini
,
one can quite dramatically reduce the memory footprint:
[Database] FileExtend = 100 ; down from 200 MaxCheckpointRemap = 1000 ; down from 2000 [TempDatabase] MaxCheckpointRemap = 1000 ; down from 2000 [Parameters] ServerThreads = 5 ; down from 10 CheckpointInterval = 10 ; down from 60 NumberOfBuffers = 100 ; down from 2000 MaxDirtyBuffers = 50 ; down from 1200 SchedulerInterval = 5 ; down from 10 FreeTextBatchSize = 1000 ; down from 100000 [HTTPServer] ServerThreads = 2 ; down from 5 KeepAliveTimeout = 5 ; down from 10 HTTPThreadSize = 10000 ; down from 280000 [Client] SQL_PREFETCH_ROWS = 10 ; down from 100 SQL_PREFETCH_BYTES = 4096 ; down from 16000 [Replication] ServerEnable = 0 ; changed from 1 [Zero Config] ;ServerName = virtuoso (SAUCE) ; commented-out [SPARQL] ResultSetMaxRows = 10000 ; down from 100000 [Plugins] ; ... ; comment-out all plugins
Result:
default empty database with no Conductor installed | 12M |
Virtual memory allocation | 150M |
Resident memory used | 70M |
Executing status()
shows that 1000 buffers
are allocated and only 270 are in use.
Comparison with LAMP
On the same machine, we installed Apache 2.x and MySQL 5.0 server using standard Debian GNU/Linux packages:
bash$ sudo apt-get install mysql-server apache2
This is not quite comparing like with like; Virtuoso includes not only HTTP and SQLinterfaces, but also a complete RDF Quad-store, SPARQL processor, free-text indexer, etc. However, out-of-the-box MySQL and Apache consumptions compare to the above-tuned Virtuoso as follows:
Apache | MySQL | Virtuoso | |
package *.deb | 45.6 M | - | 58 M |
server binary | 0.3 M | 7 M | 8.3 M |
default empty database | - | 21 M | 12 M |
virtual memory allocation | 229 M | 123 M | 350 M |
resident memory usage | 2.8 M | 15 M | 70 M |
Enterprise-wide
In larger installations, the NumberOfBuffers parameter should be increased, but there is no point in making the process so large it has to swap. Therefore we recommend about 60% memory should be allocated to buffers.
As an example, we consider two instances: our own web-server, www.openlinksw.com (running on Debian GNU/Linux), and DBpedia.org (running on Sun Solaris).
www | DBpedia | |
Virtual memory allocated | 2734M | 6257M |
Resident memory | 662M (65%) | 6216M (38%) |
Striping | 0 | 0 |
CheckpointInterval | 120 | 60 |
NumberOfBuffers | 20000, 18511 used | 100000, 99964 used |
MaxDirtyBuffers | 8000 | 40000 |
MaxCheckpointRemap | 16000 | 80000 |
FreeTextBatchSize | 100000 | 100000 |
ServerThreads | 10 | 1000 |
HTTP ServerThreads | 250 | 100 |
HTTPThreadSize | 280000 | 10000000 |
Plugins | only wikiv | wikiv, imagemagick, wbxml2 |
SPARQL ResultSetMaxRows | 1000 | 1000 |
References
- Virtuoso performance diagnostics
- Virtuoso performance tuning