SDB Loading performance

Introduction

Performance reporting is an area prone to misinterpretation, and such reports should be liberally decorated with disclaimers. In our case there are an alarming number of variables: the hardware, the operating system, the database engine and its myriad parameters, the data itself, the queries, and planetary alignment.

Given this here is some basic information. You may find it sufficient:

  • Loading speed will be in the thousands of triples per second range. Expect to load around 5 million triples per hour.
  • Index layout is usually better than hash for loading speed. Hash loading is very bad on MySQL.
  • Hash layout is better for query speed.

We suggest that you don’t choose your database based on these figures. The performance is broadly similar, so if you already have a relational database installed this is your best option.

The Databases and Hardware

SDB supports a range of databases, but the figures here are limited to SQLServer and Postgresql. The hardware used was identical, although running linux (for Postgresql) and windows (for SQLServer).

Hardware

  • Dual AMD Opteron processors, 64 bit, 1.8 GHz.
  • 8 GB memory.
  • 80 GB disk for database.

Windows setup

  • Windows server 2003
  • Java 6 64 bit
  • SQLServer 2005

Linux setup

  • Redhat Enterprise Linux 4
  • Java 6 64 bit
  • Postgresql 8.2

The Dataset and Queries

We use the Lehigh University Benchmark http://swat.cse.lehigh.edu/projects/lubm/ and dbpedia http://dbpedia.org/, together with some example queries that each provides. You can find the queries in SDB/PerfTests.

LUBM

LUBM generates artificial datasets. To be useful one needs to apply reasoning, and this was done in advance of loading. The queries are quite stressful for SDB in that they are not very ground (in many neither subjects nor objects are present), and many produce very large result sets. Thus they are probably atypical of many SPARQL queries.

  • Size: 19 million triples (including inferred triples).

dbpedia

The dbpedia queries are, unlike LUBM, quite ground. dbpedia contains many large literals, in contrast to LUBM.

  • Size: 25 million triples.

Loading

All operations were performed using SDB’s command line tools. The data was loaded into a freshly formatted SDB store – although postgresql needs an ANALYSE to avoid silly planning – then the additional indexes were added.

Results

Benchmark Database loading Speed (tps) Index time (s) Size (MB)
LUBM Postgres (Hash) 4972 199 5124
LUBM Postgres (Index) 8658 176 3666
LUBM SQLServer (Hash) 8762 121 3200
LUBM SQLServer (Index) 7419 68 2029
DBpedia Postgres (Hash) 3029 298 10193
DBpedia Postgres (Index) 4293 227 6251
DBpedia SQLServer (Hash) 5345 162 6349
DBpedia SQLServer (Index) 4749 110 4930

Uniprot 700m loading: Tuning Helps

To illustrate the variability in loading speed, and emphasise the importance of tuning, consider the case of Uniprot http://dev.isb-sib.ch/projects/uniprot-rdf/. Uniprot contains (at the time of writing) around 700 million triples. We loaded these on to the SQLServer setup given above, but with the following changes:

  • The database was stored on a separate disk.
  • The database’s transactional logs were stored on yet another disk.

So the rdf data, database data, and log data were all on distinct disks.

Loading into an index-layout store proceeded at:

  • 11079 triples per second