Peter Keegan wrote:
I ran a query performance tester against 8-cpu and 16-cpu Xeon servers
(16/32 cpu hyperthreaded). on Linux. Here are the results:
8-cpu: 275 qps
16-cpu: 305 qps
(the dual-core Opteron servers are still faster)
Here is the stack trace of 8 of the 16 query threads during the test:
at org.apache.lucene.index.SegmentReader.document(SegmentReader.java
:281)
- waiting to lock <0x0000002adf5b2110> (a
org.apache.lucene.index.SegmentReader)
at org.apache.lucene.search.IndexSearcher.doc(IndexSearcher.java:83)
at org.apache.lucene.search.MultiSearcher.doc(MultiSearcher.java
:146)
at org.apache.lucene.search.Hits.doc(Hits.java:103)
SegmentReader.document is a synchronized method. I have one stored field
(binary, uncompressed) with and average length of 0.5Kb. The retrieval of
this stored field is within this synchronized code. Since I am using
MMapDirectory, does this retrieval need to be synchronized?
Yes, since in FieldReader the file positions must be synchronized.
The way to avoid this would be to:
1. Add a clone() method to FieldReader that clones it's two IndexInputs.
2. Add a ThreadLocal to SegmentReader whose value is a cloned FieldReader.
3. Use the ThreadLocal's FieldReader in the document() method.
TermInfosReader has a similar optimization, using a ThreadLocal
containing a SegmentTermEnum for each thread.
Doug
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