Hi, This means I got a serious flaw in my column family design. At this moment I am storing sensor data into the database, rowkey is the sensor ID, supercolumn is the timestamp, and the different columns in the supercolumn are sensor readings.
This means with my current design it is almost impossible to ‘delete’ data from disk unless doing a major compaction on all the sstables ? (all sstables will contain the same rowkey) And at this moment new data is being loaded every 5 minutes, which means it would be big troubles to do the major compaction. Is this correct what I am thinking? Kind regards, Pieter Callewaert From: Yuki Morishita [mailto:mor.y...@gmail.com] Sent: dinsdag 22 mei 2012 16:21 To: user@cassandra.apache.org Subject: Re: supercolumns with TTL columns not being compacted correctly Data will not be deleted when those keys appear in other stables outside of compaction. This is to prevent obsolete data from appearing again. yuki On Tuesday, May 22, 2012 at 7:37 AM, Pieter Callewaert wrote: Hi Samal, Thanks for your time looking into this. I force the compaction by using forceUserDefinedCompaction on only that particular sstable. This gurantees me the new sstable being written only contains the data from the old sstable. The data in the sstable is more than 31 days old and gc_grace is 0, but still the data from the sstable is being written to the new one, while I am 100% sure all the data is invalid. Kind regards, Pieter Callewaert From: samal [mailto:samalgo...@gmail.com] Sent: dinsdag 22 mei 2012 14:33 To: user@cassandra.apache.org<mailto:user@cassandra.apache.org> Subject: Re: supercolumns with TTL columns not being compacted correctly Data will remain till next compaction but won't be available. Compaction will delete old sstable create new one. On 22-May-2012 5:47 PM, "Pieter Callewaert" <pieter.callewa...@be-mobile.be<mailto:pieter.callewa...@be-mobile.be>> wrote: Hi, I’ve had my suspicions some months, but I think I am sure about it. Data is being written by the SSTableSimpleUnsortedWriter and loaded by the sstableloader. The data should be alive for 31 days, so I use the following logic: int ttl = 2678400; long timestamp = System.currentTimeMillis() * 1000; long expirationTimestampMS = (long) ((timestamp / 1000) + ((long) ttl * 1000)); And using this to write it: sstableWriter.newRow(bytes(entry.id<http://entry.id>)); sstableWriter.newSuperColumn(bytes(superColumn)); sstableWriter.addExpiringColumn(nameTT, bytes(entry.aggregatedTTMs), timestamp, ttl, expirationTimestampMS); sstableWriter.addExpiringColumn(nameCov, bytes(entry.observationCoverage), timestamp, ttl, expirationTimestampMS); sstableWriter.addExpiringColumn(nameSpd, bytes(entry.speed), timestamp, ttl, expirationTimestampMS); This works perfectly, data can be queried until 31 days are passed, then no results are given, as expected. But the data is still on disk until the sstables are being recompacted: One of our nodes (we got 6 total) has the following sstables: [cassandra@bemobile-cass3 ~]$ ls -hal /data/MapData007/HOS-* | grep G -rw-rw-r--. 1 cassandra cassandra 103G May 3 03:19 /data/MapData007/HOS-hc-125620-Data.db -rw-rw-r--. 1 cassandra cassandra 103G May 12 21:17 /data/MapData007/HOS-hc-163141-Data.db -rw-rw-r--. 1 cassandra cassandra 25G May 15 06:17 /data/MapData007/HOS-hc-172106-Data.db -rw-rw-r--. 1 cassandra cassandra 25G May 17 19:50 /data/MapData007/HOS-hc-181902-Data.db -rw-rw-r--. 1 cassandra cassandra 21G May 21 07:37 /data/MapData007/HOS-hc-191448-Data.db -rw-rw-r--. 1 cassandra cassandra 6.5G May 21 17:41 /data/MapData007/HOS-hc-193842-Data.db -rw-rw-r--. 1 cassandra cassandra 5.8G May 22 11:03 /data/MapData007/HOS-hc-196210-Data.db -rw-rw-r--. 1 cassandra cassandra 1.4G May 22 13:20 /data/MapData007/HOS-hc-196779-Data.db -rw-rw-r--. 1 cassandra cassandra 401G Apr 16 08:33 /data/MapData007/HOS-hc-58572-Data.db -rw-rw-r--. 1 cassandra cassandra 169G Apr 16 17:59 /data/MapData007/HOS-hc-61630-Data.db -rw-rw-r--. 1 cassandra cassandra 173G Apr 17 03:46 /data/MapData007/HOS-hc-63857-Data.db -rw-rw-r--. 1 cassandra cassandra 105G Apr 23 06:41 /data/MapData007/HOS-hc-87900-Data.db As you can see, the following files should be invalid: /data/MapData007/HOS-hc-58572-Data.db /data/MapData007/HOS-hc-61630-Data.db /data/MapData007/HOS-hc-63857-Data.db Because they are all written more than an moth ago. gc_grace is 0 so this should also not be a problem. As a test, I use forceUserSpecifiedCompaction on the HOS-hc-61630-Data.db. Expected behavior should be an empty file is being written because all data in the sstable should be invalid: Compactionstats is giving: compaction type keyspace column family bytes compacted bytes total progress Compaction MapData007 HOS 11518215662 532355279724 2.16% And when I ls the directory I find this: -rw-rw-r--. 1 cassandra cassandra 3.9G May 22 14:12 /data/MapData007/HOS-tmp-hc-196898-Data.db The sstable is being 1-on-1 copied to a new one. What am I missing here? TTL works perfectly, but is it giving a problem because it is in a super column, and so never to be deleted from disk? Kind regards Pieter Callewaert | Web & IT engineer Be-Mobile NV<http://www.be-mobile.be/> | TouringMobilis<http://www.touringmobilis.be/> Technologiepark 12b - 9052 Ghent - Belgium Tel + 32 9 330 51 80 | Fax + 32 9 330 51 81 | Cell + 32 473 777 121
