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From Erik Forsberg <forsb...@opera.com>
Subject sstable size increase at compaction
Date Wed, 21 Mar 2012 15:36:45 GMT
Hi!

We're using the bulkloader to load data to Cassandra. During and after 
bulkloading, the minor compaction process seems to result in larger 
sstables being created. An example:

  INFO [CompactionExecutor:105] 2012-03-21 15:18:46,608 
CompactionTask.java (line 115) Compacting [SSTableReader(pat
h='/cassandra/OSP5/Data/OSP5-Data-hc-1755-Data.db'), (REMOVED A BUNCH OF 
OTHER SSTABLE PATHS), 
SSTableReader(path='/cassandra/OSP5/Data/OSP5-Data-hc-1749-Data.db'), 
SSTableReader(path='/cassandra/O
SP5/Data/OSP5-Data-hc-1753-Data.db')]

  INFO [CompactionExecutor:105] 2012-03-21 15:30:04,188 
CompactionTask.java (line 226) Compacted to 
[/cassandra/OSP5/Data/OSP5-Data-hc-3270-Data.db,].  84,214,484 to 
105,498,673 (~125% of original) bytes for 2,132,056 keys at 
0.148486MB/s.  Time: 677,580ms.

The sstables are compressed (DeflateCompressor with chunk size 128) on 
the Hadoop cluster before being transferred to Cassandra, and the CF has 
the same compression settings:

[default@Keyspace1] describe Data;
     ColumnFamily: Data (Super)
       Key Validation Class: org.apache.cassandra.db.marshal.UTF8Type
       Default column value validator: 
org.apache.cassandra.db.marshal.LongType
       Columns sorted by: 
org.apache.cassandra.db.marshal.LongType/org.apache.cassandra.db.marshal.UTF8Type
       GC grace seconds: 864000
       Compaction min/max thresholds: 4/32
       Read repair chance: 1.0
       DC Local Read repair chance: 0.0
       Replicate on write: true
       Caching: KEYS_ONLY
       Bloom Filter FP chance: 0.01
       Built indexes: []
       Compaction Strategy: 
org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
       Compression Options:
         chunk_length_kb: 128
         sstable_compression: 
org.apache.cassandra.io.compress.DeflateCompressor

Any clues on this?

Regards,
\EF

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