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From "Andy Seaborne (Commented) (JIRA)" <>
Subject [jira] [Commented] (JENA-178) SPARQL Results serialization is slow for some formats with large result sets
Date Tue, 27 Dec 2011 11:50:30 GMT


Andy Seaborne commented on JENA-178:

I changed all Stacks<> in ARQ to Deque<>.  This was a Java6 change due that I'd
not got round to doing.  

This changed XML from about 7000 to 5000 (not completely sound test though - the machine was
long running TDB tests at the time so the absolute number isn't meaningful).

The test program Jena178 does not allow for JITting.  Attached is Jena178_ResultSetSpeed.
 It makes more difference to the first-run tests presumably because low-level code is being
worked out and it benefits later code.

The JSON looks slow and IndentedWriter is a common component.  It does do per-character poking.
 Making it final did not help.  Checking for newlines in printed strings makes some difference.

BufferingWriter looks suspicious even after the encoder improvements after looking with visualvm.
 It should buffer in string-space, not in byte-space.

We could swap to StAX.  Any reason why not?

Current figures:

-- checking for newlines inside strings
XMLSAX out took: 273
XMLStax out took: 272
XML out took: 1940
XML in took: 397
TSV out took: 128
TSV in took: 330
JSON out took: 1782
JSON in took: 746
-- not checking for newlines inside strings.
XMLSAX out took: 326
XMLStax out took: 274
XML out took: 840
XML in took: 452
TSV out took: 130
TSV in took: 306
JSON out took: 908
JSON in took: 761

OpenJDK Runtime Environment (IcedTea6 1.11pre) (6b23~pre11-0ubuntu1.11.10)
OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)

> SPARQL Results serialization is slow for some formats with large result sets
> ----------------------------------------------------------------------------
>                 Key: JENA-178
>                 URL:
>             Project: Jena
>          Issue Type: Bug
>          Components: ARQ
>    Affects Versions: ARQ 2.9.0
>         Environment: Windows 7 Enterprise 64 bit
>            Reporter: Rob Vesse
>            Assignee: Damian Steer
>             Fix For: ARQ 2.9.1
>         Attachments:, Jena178.patch,,,
> The SPARQL XML and JSON Result formats are very slow when the result set is large.  This
is surprising to me since both formats are relatively simple and should lend themselves to
fairly fast streaming serialization and parsing.
> The following are observed performance figures comparing SPARQL XML, SPARQL JSON and
SPARQL TSV results format.  This is the averaged time over 5 runs to retrieve the first 50,000
triples from the dataset with a simple SELECT * WHERE { ?s ?p ?o } LIMIT 50000 via a HTTP
request to Fuseki and iterate over the results on the client.
> SPARQL XML = 15.25 seconds
> SPARQL JSON = 10.9 seconds
> SPARQL TSV = 0.54 seconds
> Now obviously TSV is way simpler to serialize and parse than XML/JSON but these serializers
and parsers should not be 20-30 times slower IMO
> Also for comparison note that doing an equivalent CONSTRUCT { ?s ?p ?p } WHERE { ?s ?p
?o } LIMIT 50000 takes only about 2s and that is using RDF/XML serialization which I would
have expected to be slower because RDF/XML is more complex to generate than either SPARQL
XML/JSON results.  I haven't dived into the code in detail to investigate why this is slow
yet but do the Jena team have any thoughts on this?

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