Daniel Debray created SOLR-5855:
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Summary: Increasing solr highlight performance with caching
Key: SOLR-5855
URL: https://issues.apache.org/jira/browse/SOLR-5855
Project: Solr
Issue Type: Improvement
Components: highlighter
Affects Versions: 5.0
Reporter: Daniel Debray
Hi folks,
while investigating possible performance bottlenecks in the highlight component
i discovered two places where we can save some cpu cylces.
Both are in the class org.apache.solr.highlight.DefaultSolrHighlighter
First in method doHighlighting (lines 411-417):
In the loop we try to highlight every field that has been resolved from the
params on each document. Ok, but why not skip those fields that are not present
on the current document?
So i changed the code from:
for (String fieldName : fieldNames) {
fieldName = fieldName.trim();
if( useFastVectorHighlighter( params, schema, fieldName ) )
doHighlightingByFastVectorHighlighter( fvh, fieldQuery, req, docSummaries,
docId, doc, fieldName );
else
doHighlightingByHighlighter( query, req, docSummaries, docId, doc,
fieldName );
}
to:
for (String fieldName : fieldNames) {
fieldName = fieldName.trim();
if (doc.get(fieldName) != null) {
if( useFastVectorHighlighter( params, schema, fieldName ) )
doHighlightingByFastVectorHighlighter( fvh, fieldQuery, req,
docSummaries, docId, doc, fieldName );
else
doHighlightingByHighlighter( query, req, docSummaries, docId, doc,
fieldName );
}
}
The second place is where we try to retrieve the TokenStream from the document
for a specific field.
line 472:
TokenStream tvStream =
TokenSources.getTokenStreamWithOffsets(searcher.getIndexReader(), docId,
fieldName);
where..
public static TokenStream getTokenStreamWithOffsets(IndexReader reader, int
docId, String field) throws IOException {
Fields vectors = reader.getTermVectors(docId);
if (vectors == null) {
return null;
}
Terms vector = vectors.terms(field);
if (vector == null) {
return null;
}
if (!vector.hasPositions() || !vector.hasOffsets()) {
return null;
}
return getTokenStream(vector);
}
keep in mind that we currently hit the IndexReader n times where n = requested
rows(documents) * requested amount of highlight fields.
in my usecase reader.getTermVectors(docId) takes around 150.000~250.000ns on a
warm solr and 1.100.000ns on a cold solr.
If we store the returning Fields vectors in a cache, this lookups only take
25000ns.
I would suggest something like the following code in the
doHighlightingByHighlighter method in the DefaultSolrHighlighter class (line
472):
Fields vectors = null;
SolrCache termVectorCache = searcher.getCache("termVectorCache");
if (termVectorCache != null) {
vectors = (Fields) termVectorCache.get(Integer.valueOf(docId));
if (vectors == null) {
vectors = searcher.getIndexReader().getTermVectors(docId);
if (vectors != null) termVectorCache.put(Integer.valueOf(docId), vectors);
}
} else {
vectors = searcher.getIndexReader().getTermVectors(docId);
}
TokenStream tvStream = TokenSources.getTokenStreamWithOffsets(vectors,
fieldName);
and TokenSources class:
public static TokenStream getTokenStreamWithOffsets(Fields vectors, String
field) throws IOException {
if (vectors == null) {
return null;
}
Terms vector = vectors.terms(field);
if (vector == null) {
return null;
}
if (!vector.hasPositions() || !vector.hasOffsets()) {
return null;
}
return getTokenStream(vector);
}
4000ms on 1000 docs without cache
639ms on 1000 docs with cache
102ms on 30 docs without cache
22ms on 30 docs with cache
on an index with 190.000 docs with a numFound of 32000 and 80 different
highlight fields.
I think querys with only one field to highlight on a document does not benefit
that much from a cache like this, thats why i think an optional cache would be
the best solution there.
As i saw the FastVectorHighlighter uses more or less the same approach and
could also benefit from this cache.
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