Thomas Mueller created OAK-853:
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Summary: Many child nodes: Diffing causes many calls to
MicroKernel.getNodes
Key: OAK-853
URL: https://issues.apache.org/jira/browse/OAK-853
Project: Jackrabbit Oak
Issue Type: Improvement
Components: core
Reporter: Thomas Mueller
Creating a flat hierarchy of the following form causes many calls to
MicroKernel.getNodes and is thus slow.
{code}
for (int i = 0; i < 10000; i++) {
root.addNode("test" + i, "nt:folder");
if (i % 1000 == 0) {
session.save();
}
}
{code}
As far as I see, this isn't just the case for MicroKernel based storage, but
also for the SegmentNodeStore. The reason seems to be that the optimization for
many child nodes in KernelNodeState.compareAgainstBaseState and
SegmentNodeState.compareAgainstBaseState that avoids iterating over all
children doesn't work.
The optimization uses:
{code}
if (base instanceof SegmentNodeState) ...
if (base instanceof KernelNodeState) ...
{code}
Ideally, the instanceof should be avoided, but I'm not sure how to do that yet.
Anyway, the problem is that "base" is a ModifiedNodeState so no optimization
can be used.
I was thinking, couldn't the ModifiedNodeState do a reverse diff in this case?
That is, inside ModifiedNodeState.compareAgainstBaseState, check if the "base"
parameter is a ModifiedNodeState, and the "base" field is not, then do a
reverse diff, which would be efficient. (We should probably not use "base" for
both the field name and the parameter; well that's a change for another time.)
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