AllegroGraph 2.0 Performance Tuning

AllegroGraph is a Persistent Database for RDF Triples designed especially for 64-bit systems to support huge databases. We have succesfully loaded databases containing several billions of triples using an AMD OpteronTM 844 running at 1.8 GHz, with 128 KB of L1 cache, 1MB of L2 cache, 16 GB of ECC RAM, and running Linux 2.6.18.

Please read the following guidelines for configuring your system.

Performance Tuning Tips For 64-bit Systems

There are two important variables that you can use to tune memory use.

[1] ags.setDefaultExpectedResources();

The main factor that determines memory usage is the number of unique resources and literals present and their total size in the RDF input file(s). One way to optimize the number of triples in your system is to set the number of expected resources when opening a triple store. This will immediately allocate the right amount of memory and your image size won't grow much beyond that. If you set the initial value too small, the string table will have to be rebuilt, possibly many times, and more memory will be used.

[2] ags.setChunkSize()

Before the triples are committed to disk they are indexed in memory. This variable determines how many triples will be indexed at a time. If you have only 4 Gig you might consider reducing the default setting for this variable somewhat.

A typical run of the 44 Million Triples Wikipedia RDF file on a 16 GB AMD Opteron running Linux yields the following results:

Table 1, Wikipedia RDF File, 44 Million Triples

The parameter setting for DefaultExpectedResource is 10,000,000 and the ChunkSize is set to 10,000,000.

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