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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-5693) don't write deleted documents on flush
Date Thu, 22 May 2014 00:23:38 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-5693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14005450#comment-14005450
] 

Robert Muir commented on LUCENE-5693:
-------------------------------------

{quote}
I disagree: I think we discover places that are "relying" on deleted docs behavior, i.e. test
bugs. When I did this on LUCENE-5675 there were only a few places that relied on deleted docs.
{quote}

That's not the complexity i'm concerned about. I'm talking about bugs in lucene itself because
shit like the following happens:
* various codec apis unable to cope with writing 0 doc segments because all the docs were
deleted
* various codec apis with corner case bugs because stuff like 'maxdoc' in segmentinfo they
are fed is inconsistent with what they saw.
* various index/search apis unable to cope with docid X appears in codec api Y but not codec
api Z where its expected to exist.
* slow O(n) passes thru indexwriter apis to recalculate and reshuffle ordinals and stuff like
that.
* corner case bugs like incorrect statistics.
* additional complexity inside indexwriter/codecs to handle this, when just merging away would
be better.

So if we want to rename the issue to "as a special case, don't write deleted postings on flush"
and remove the TODO about changing this for things like DV, then I'm fine.

But otherwise, if this is intended to be a precedent of how things should work, then I strongly
feel we should not do this. The additional complexity and corner cases are simply not worth
it.

> don't write deleted documents on flush
> --------------------------------------
>
>                 Key: LUCENE-5693
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5693
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>         Attachments: LUCENE-5693.patch
>
>
> When we flush a new segment, sometimes some documents are "born deleted", e.g. if the
app did a IW.deleteDocuments that matched some not-yet-flushed documents.
> We already compute the liveDocs on flush, but then we continue (wastefully) to send those
known-deleted documents to all Codec parts.
> I started to implement this on LUCENE-5675 but it was too controversial.
> Also, I expect typically the number of deleted docs is 0, or small, so not writing "born
deleted" docs won't be much of a win for most apps.  Still it seems silly to write them, consuming
IO/CPU in the process, only to consume more IO/CPU later for merging to re-delete them.



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