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https://issues.apache.org/jira/browse/LUCENE-4536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13491456#comment-13491456
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Adrien Grand commented on LUCENE-4536:
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bq. This patch only changes the on-disk format right? The specialized in-memory
readers are still backed by native arrays (short[]/int[]/long[], etc.)?
Exactly.
bq. Ie, in general, I think the version constants should be created once and
then not changed (write once), and VERSION_CURRENT changes to point to
whichever is most recent.
Ok, I'll change it.
bq. That careful anonymous subclass in PackedInts to handle seeking to the end
when the last value is read is sort of sneaky ... this should only kick in when
reading the old (long-aligned) format right?
This only happens when reading the old format AND the number of bytes used to
serialized the array is not a multiple of 8. I'll add an assert to make sure
that this condition can only be true with the old format.
bq. Or ... maybe... we should not "promise" this (no trailing wasted bytes) in
the API?
bq. Or maybe we expose a new explicit method to "seek to the end of this packed
ints" or something (eg maybe "skipTrailingBytes").
These were my first ideas, but the truth is that I was very scared to break
something (for example doc values rely on the assumption that after reading the
last value of a direct array, the whole stream is consumed). Fixing PackedInts
to make sure those assumptions are still true looked easier to me as I was able
to create "fake" long-aligned packed ints and make sure that the whole stream
was consumed after reading the last value.
But your option makes perfect sense to me and I will do it if you think it is
cleaner.
Thanks for the review!
> Make PackedInts byte-aligned?
> -----------------------------
>
> Key: LUCENE-4536
> URL: https://issues.apache.org/jira/browse/LUCENE-4536
> Project: Lucene - Core
> Issue Type: Task
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: 4.1
>
> Attachments: LUCENE-4536.patch
>
>
> PackedInts are more and more used to save/restore small arrays, but given
> that they are long-aligned, up to 63 bits are wasted per array. We should try
> to make PackedInts storage byte-aligned so that only 7 bits are wasted in the
> worst case.
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