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From Apache Wiki <wikidi...@apache.org>
Subject [Solr Wiki] Trivial Update of "UpdateXmlMessages" by YonikSeeley
Date Sun, 06 Nov 2011 23:06:58 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Solr Wiki" for change notification.

The "UpdateXmlMessages" page has been changed by YonikSeeley:
http://wiki.apache.org/solr/UpdateXmlMessages?action=diff&rev1=35&rev2=36

Comment:
reword

  A commit operation makes index changes visible to new search requests.
  A '''hard commit''' also calls fsync on the index files to ensure they have been flushed
to stable storage and no data loss will result from a power failure.
  
- A '''soft commit''' is much faster since it only makes index changes visible and does not
fsync index files or write a new index descriptor.  If the JVM crashes or there is a loss
of power, only changes that occurred before the last '''hard commit''' will be visible.  Search
collections that have near-real-time requirements (that want index changes to be quickly visible
to searches) will want to soft commit often but hard commit less frequently.
+ A '''soft commit''' is much faster since it only makes index changes visible and does not
fsync index files or write a new index descriptor.  If the JVM crashes or there is a loss
of power, changes that occurred after the last '''hard commit''' will be lost.  Search collections
that have near-real-time requirements (that want index changes to be quickly visible to searches)
will want to soft commit often but hard commit less frequently.
  
  An '''optimize''' is like a '''hard commit''' except that it forces all of the index segments
to be merged into a single segment first.  Depending on the use cases, this operation should
be performed infrequently, if at all, since it involves reading and re-writing the entire
index.  Segments are normally merged over time anyway (as determined by the merge policy),
and optimize just forces these merges to occur immediately.
  

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