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https://issues.apache.org/jira/browse/LUCENE-10033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17402726#comment-17402726
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weizijun commented on LUCENE-10033:
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Hi, [~jpountz], [~gsmiller], I am not familiar with luceneutil yet, I am
working on it. After I get the results, I will send the test results.
I found the key reason, that why common compression algorithms have a nice
compression ratio in time series data.
The data sets of the time series line are often similar. But in a block, there
The time series line data sets are continuous, and often similar, but there may
be multiple time series line data sets in a block, but the data difference
between the time series line may be large. And time series metric fields are
often double.
I push a test case named `testTimeSeries` in
TestDocValuesEncoder,TestLZ4DocValuesEncoder,TestDeltaLZ4DocValuesEncoder.
The encode length result is :
||Encoder||Length||
|DocValuesEncoder|1036|
|LZ4DocValuesEncoder|46|
|DeltaLZ4DocValuesEncoder|49|
> Encode doc values in smaller blocks of values, like postings
> ------------------------------------------------------------
>
> Key: LUCENE-10033
> URL: https://issues.apache.org/jira/browse/LUCENE-10033
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Time Spent: 1h
> Remaining Estimate: 0h
>
> This is a follow-up to the discussion on this thread:
> https://lists.apache.org/thread.html/r7b757074d5f02874ce3a295b0007dff486bc10d08fb0b5e5a4ba72c5%40%3Cdev.lucene.apache.org%3E.
> Our current approach for doc values uses large blocks of 16k values where
> values can be decompressed independently, using DirectWriter/DirectReader.
> This is a bit inefficient in some cases, e.g. a single outlier can grow the
> number of bits per value for the entire block, we can't easily use run-length
> compression, etc. Plus, it encourages using a different sub-class for every
> compression technique, which puts pressure on the JVM.
> We'd like to move to an approach that would be more similar to postings with
> smaller blocks (e.g. 128 values) whose values get all decompressed at once
> (using SIMD instructions), with skip data within blocks in order to
> efficiently skip to arbitrary doc IDs (or maybe still use jump tables as
> today's doc values, and as discussed here for postings:
> https://lists.apache.org/thread.html/r7c3cb7ab143fd4ecbc05c04064d10ef9fb50c5b4d6479b0f35732677%40%3Cdev.lucene.apache.org%3E).
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