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https://issues.apache.org/jira/browse/JENA-813?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14204914#comment-14204914
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Rob Vesse commented on JENA-813:
--------------------------------
Ideally the iterators here should be constructed lazily as possible rather than
needing to request and append together all the iterators in advance but this
looks like quite a big refactor so I wanted to get some input on how best to
resolve this
> In-memory DatasetGraph is extremely slow to iterate over when lots of named
> graphs are used
> -------------------------------------------------------------------------------------------
>
> Key: JENA-813
> URL: https://issues.apache.org/jira/browse/JENA-813
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
> Affects Versions: Jena 2.12.1
> Reporter: Rob Vesse
> Attachments: SlowDatasetGraph.java
>
>
> Discovered this accidentally in the course of debugging a test case which
> seemed to running exceptionally slow. Basically the in-memory
> {{DatasetGraph}} implementation will perform extremely poorly when trying to
> iterate all quads it contains.
> This problem manifests at relatively small scales and shows a marked
> difference between small numbers of quads in a single graph versus the quads
> in individual graphs. In my testing with only a few thousand quads placing
> them in a single graph versus many individual graphs can see 5/6 orders of
> magnitude performance difference.
> I will attach code to reproduce and show my log output from running this on
> my system (Mac OS X Mavericks - Quad Core - 8GB RAM):
> {noformat}
> 0 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Testing with
> 1000 quads
> 31 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 44 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 1000 quads
> in 1 graphs
> 64 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took 0.009692
> seconds to iterate over 1000 quads in 1 graphs
> 64 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 85 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 1000 quads
> in 1000 graphs
> 779 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took 0.693548
> seconds to iterate over 1000 quads in 1000 graphs
> 779 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Testing with
> 2000 quads
> 779 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 788 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 2000 quads
> in 1 graphs
> 788 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took 0.000047
> seconds to iterate over 2000 quads in 1 graphs
> 788 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 821 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 2000 quads
> in 2000 graphs
> 7735 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took 6.914044
> seconds to iterate over 2000 quads in 2000 graphs
> 7735 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Testing with
> 3000 quads
> 7735 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 7743 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 3000 quads
> in 1 graphs
> 7743 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took 0.000032
> seconds to iterate over 3000 quads in 1 graphs
> 7743 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 7767 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 3000 quads
> in 3000 graphs
> 36233 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took
> 28.465885 seconds to iterate over 3000 quads in 3000 graphs
> 36233 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Testing with
> 4000 quads
> 36233 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 36234 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 4000 quads
> in 1 graphs
> 36235 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took
> 0.000033 seconds to iterate over 4000 quads in 1 graphs
> 36235 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 36253 [main] INFO org.apache.jena.playground.SlowDatasetGraph - DatasetGraph
> implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has 4000 quads
> in 4000 graphs
> 109646 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took
> 73.393265 seconds to iterate over 4000 quads in 4000 graphs
> 109646 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Testing
> with 5000 quads
> 109646 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 109648 [main] INFO org.apache.jena.playground.SlowDatasetGraph -
> DatasetGraph implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has
> 5000 quads in 1 graphs
> 109648 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took
> 0.000066 seconds to iterate over 5000 quads in 1 graphs
> 109648 [main] DEBUG com.hp.hpl.jena.shared.LockMRSW - Lock : main
> 109654 [main] INFO org.apache.jena.playground.SlowDatasetGraph -
> DatasetGraph implementation com.hp.hpl.jena.sparql.core.DatasetGraphMaker has
> 5000 quads in 5000 graphs
> 249867 [main] INFO org.apache.jena.playground.SlowDatasetGraph - Took
> 140.212082 seconds to iterate over 5000 quads in 5000 graphs
> {noformat}
> From debugging my best guess is this is down to how
> {{DatasetGraphCollection}} (and it's hierarchy) build the quads iterator by
> iterating over the graph names and then iterating over the individual graphs
> appending the iterators together. Something in the structuring means
> accessing and appending all those individual iterators is drastically slow
> compared to iterating a single graph.
> A related bug is that given a sufficiently large number of graphs attempts to
> iterate will fail with a {{StackOverflowError}}, the culprit in this case is
> {{IteratorCons}}.
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