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https://issues.apache.org/jira/browse/LUCENE-5052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13937947#comment-13937947
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Mikhail Khludnev commented on LUCENE-5052:
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bq. it'd be better if the postings format wrapped another postings format, and
then only used the bitset when the docFreq was high enough
There are two orthogonal conceptions:
* particular format - let's generalize "bitset format" to "no-tf format", and
use WAH8, Elas-Fano with off-heap access (TODO). Thus, it works for spare
postings;
* API - how consumer can express his intention to use "no-tf" format? e.g.
TermFilter or TermsEnum.docs() with special flag;
I'd like to clarify use-case for this issue (issue summary might need to be
improved). It aims Solr's fq or even Heliosearch's GC-lightness. I suppose that
user can decide which fields to index with "no-tf" format, these are "string"
fields. Then, user requests filtering for these fields, no scoring is needed,
for sure.
[~mikemccand]
Hence, I don't think than conditional conditional triggering is a good choice,
however I don't know how to do it. I might not understand well how pulsing
codec is used (impl idea is clear, though), can you point me on its' usage.
Thanks!
> bitset codec for off heap filters
> ---------------------------------
>
> Key: LUCENE-5052
> URL: https://issues.apache.org/jira/browse/LUCENE-5052
> Project: Lucene - Core
> Issue Type: New Feature
> Components: core/codecs
> Reporter: Mikhail Khludnev
> Labels: features
> Fix For: 5.0
>
> Attachments: LUCENE-5052.patch, bitsetcodec.zip, bitsetcodec.zip
>
>
> Colleagues,
> When we filter we don’t care any of scoring factors i.e. norms, positions,
> tf, but it should be fast. The obvious way to handle this is to decode
> postings list and cache it in heap (CachingWrappingFilter, Solr’s DocSet).
> Both of consuming a heap and decoding as well are expensive.
> Let’s write a posting list as a bitset, if df is greater than segment's
> maxdocs/8 (what about skiplists? and overall performance?).
> Beside of the codec implementation, the trickiest part to me is to design API
> for this. How we can let the app know that a term query don’t need to be
> cached in heap, but can be held as an mmaped bitset?
> WDYT?
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