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https://issues.apache.org/jira/browse/SOLR-5855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14579443#comment-14579443
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David Smiley commented on SOLR-5855:
------------------------------------
I was initially skeptical the stack traces would show anything of interest but
I am pleasantly mistaken. Apparently, getting the FieldInfos from
SlowCompositeReaderWrapper is a bottleneck. We look this up to determine if
there are payloads or not, so that we can then tell MemoryIndex to capture them
as well. FYI the call to get this was added recently in SOLR-6916
(Highlighting using payloads), its not related to term vectors -- this issue.
Can you please download the 5x branch, comment out the
{{scorer.getUsePayloads(...}} line (or set it to true if you want), and see how
it performs?
> re-use document term-vector Fields instance across fields in the
> DefaultSolrHighlighter
> ---------------------------------------------------------------------------------------
>
> Key: SOLR-5855
> URL: https://issues.apache.org/jira/browse/SOLR-5855
> Project: Solr
> Issue Type: Improvement
> Components: highlighter
> Affects Versions: Trunk
> Reporter: Daniel Debray
> Assignee: David Smiley
> Fix For: 5.2
>
> Attachments: SOLR-5855-without-cache.patch,
> SOLR-5855_with_FVH_support.patch, SOLR-5855_with_FVH_support.patch,
> highlight.patch
>
>
> 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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