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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "MemtableSSTable" by JonathanEllis
Date Thu, 12 May 2011 15:18:02 GMT
Dear Wiki user,

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

The "MemtableSSTable" page has been changed by JonathanEllis.
http://wiki.apache.org/cassandra/MemtableSSTable?action=diff&rev1=16&rev2=17

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  Since the input SSTables are all sorted by key, merging can be done efficiently, still requiring
no random i/o.  Once compaction is finished, the old SSTable files may be deleted: note that
in the worst case (a workload consisting of no overwrites or deletes) this will temporarily
require 2x your existing on-disk space used.  In today's world of multi-TB disks this is usually
not a problem but it is good to keep in mind when you are setting alert thresholds.
  
- SSTables that are obsoleted by a compaction are deleted asynchronously when the JVM performs
a GC.  You can force a GC from jconsole if necessary, but Cassandra will force one itself
if it detects that it is low on space.  A compaction marker is also added to obsolete sstables
so they can be deleted on startup if the server does not perform a GC before being restarted.
+ SSTables that are obsoleted by a compaction are deleted asynchronously when the JVM performs
a GC.  If a GC does not occur before Cassandra is shut down, Cassandra will remove them when
it restarts. You can force a GC from jconsole if necessary, but Cassandra will force one itself
if it detects that it is low on space.  A compaction marker is also added to obsolete sstables
so they can be deleted on startup if the server does not perform a GC before being restarted.
  
  ColumnFamilyStoreMBean exposes sstable space used as getLiveDiskSpaceUsed (only includes
size of non-obsolete files) and getTotalDiskSpaceUsed (includes everything).
  

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