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https://issues.apache.org/jira/browse/LUCENE-4161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13417054#comment-13417054
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Adrien Grand commented on LUCENE-4161:
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Hi! I think {{PackedInts.Format.PACKED.nblocks(bitsPerValue, n)}} should help.
It returns the number of {{long}} blocks required to store {{n}}
{{bitsPerValue}}-bits values.
On your pfor branch, I'm afraid instantiating a PackedInts.ReaderIterator for
every block would hurt performance since blocks only contain 128 values. Maybe
the easiest way to go would be to try to replace calls to
{{PackedIntsDecompress.decode*}} with calls to
{{PackedInts.BulkOperation.get/set}}. These methods are not exposed yet and
only work with longs but if it looks good to you, I should be able to come up
with something in the next few days...
> Make PackedInts usable by codecs
> --------------------------------
>
> Key: LUCENE-4161
> URL: https://issues.apache.org/jira/browse/LUCENE-4161
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/store
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: 4.0-ALPHA
>
> Attachments: LUCENE-4161.patch, LUCENE-4161.patch
>
>
> Some codecs might be interested in using
> PackedInts.{Writer,Reader,ReaderIterator} to read and write fixed-size values
> efficiently.
> The problem is that the serialization format is self contained, and always
> writes the name of the codec, its version, its number of bits per value and
> its format. For example, if you want to use packed ints to store your
> postings list, this is a lot of overhead (at least ~60 bytes per term, in
> case you only use one Writer per term, more otherwise).
> Users should be able to externalize the storage of metadata to save space.
> For example, to use PackedInts to store a postings list, one should be able
> to store the codec name, its version and the number of bits per doc in the
> header of the terms+postings list instead of having to write it once (or
> more!) per term.
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