Lukas Eder created OAK-808:
------------------------------
Summary: Significant performance issue in TargetImportHandler's
prefix mapping handling
Key: OAK-808
URL: https://issues.apache.org/jira/browse/OAK-808
Project: Jackrabbit Oak
Issue Type: Bug
Components: jcr
Affects Versions: 0.7
Reporter: Lukas Eder
While playing around with Oak, I have observed a significant performance
bottleneck in
{code}
org.apache.jackrabbit.oak.jcr.xml.TargetImportHandler
{code}
The problem can be seen in the attached Screenshot taken from a Yourkit
profiling session. The TargetImportHandler contains a reference to a
"documentContext" ListMultimap, which acts like a stack of prefix <-> namespace
mappings. To the outside, however, it is exposed as "documentPrefixMap", a
regular prefix <-> namespace mapping map, which only references the last
namespace for a prefix.
What's problematic here: "documentPrefixMap" is eagerly copied from
"documentContext" every time the latter is modified, which may happen a lot in
upstream products, such as Adobe CQ5. Instead, "documentPrefixMap" should be a
Map view exposing the desired data. An example implementation using Guava:
{code}
// Create this view once, in the constructor
this.documentPrefixMap = Maps.transformValues(documentContext.asMap(),
new Function<Collection<String>, String>() {
@Override
public String apply(Collection<String> input) {
return Iterables.getLast(input, null);
}
});
{code}
The above implementation might work, as "documentPrefixMap" is a read-only view
of the "documentContext" map. More explicit, verbose implementations may prove
to be even faster.
Before I write a patch, please let me know what you think.
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