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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-2555) Remove shared doc stores
Date Fri, 23 Jul 2010 16:26:50 GMT


Michael McCandless commented on LUCENE-2555:


bq. What are the performance implications of removing shared doc stores?

I agree we have to test this when this patch is complete. My hope is that we save in other
places (removing the interleaving step of the per-thread postings, no wait queue that serializes
writing to doc stores) so that overall we won't be slower.

Also, remember that shared doc stores is not as good an opto as it used to be, because we
are now able to bulk-copy both stored fields and term vectors during merging.

However, bulk merging only happens if the field name -> number mapping is congruent, b/w
the merged segment and the one segment being merged.

Unfortunately, you can easily unexpectedly break this (see LUCENE-1737) but eg adding diff't
fields to your docs, or adding same fields just in a different order.

> Remove shared doc stores
> ------------------------
>                 Key: LUCENE-2555
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: Realtime Branch
> With per-thread DocumentsWriters sharing doc stores across segments doesn't make much
sense anymore.
> See also LUCENE-2324.

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