If you don't want tombstones, don't generate them ;) More seriously, tombstones are generated when: - doing a DELETE - TTL expiration - set a column to NULL
However tombstones are an issue only if for the same value, you have many tombstones (i.e you keep overwriting the same values with datas and tombstones). Having 1 tombstone for 1 value is not an issue, having 1000 tombstone for 1 value is a problem. Do really your use case overwrite data with DELETE or NULL ? So that's why what you may want to know is how many tombstones you have on average when reading a value. This is available in: - nodetool cfstats ks.cf : Average tombstones per slice/Maximum tombstones per slice - JMX : org.apache.cassandra.metrics:keyspace=<ks>,name=TombstoneScannedHistogram,scope=<cf>,type=ColumnFamily Max/Count/99thPercentile/Mean 2016-11-15 10:05 GMT+01:00 Lu, Boying <boying...@dell.com>: > Thanks a lot for your help. > > > > We are using STCS strategy and not using TTL > > > > Is there any API that we can use to query the current number of tombstones > in a CF? > > > > > > > > *From:* Anuj Wadehra [mailto:anujw_2...@yahoo.co.in] > *Sent:* 2016年11月14日 22:20 > *To:* user@cassandra.apache.org > *Subject:* Re: Some questions to updating and tombstone > > > > Hi Boying, > > > > I agree with Vladimir.If compaction is not compacting the two sstables > with updates soon, disk space issues will be wasted. For example, if the > updates are not closer in time, first update might be in a big table by the > time second update is being written in a new small table. STCS wont compact > them together soon. > > > > Just adding column values with new timestamp shouldnt create any > tombstones. But if data is not merged for long, disk space issues may > arise. If you are STCS,just yo get an idea about the extent of the problem > you can run major compaction and see the amount of disk space created with > that( dont do this in production as major compaction has its own side > effects). > > > > Which compaction strategy are you using? > > Are these updates done with TTL? > > > > Thanks > Anuj > > > > On Mon, 14 Nov, 2016 at 1:54 PM, Vladimir Yudovin > > <vla...@winguzone.com> wrote: > > Hi Boying, > > > > UPDATE write new value with new time stamp. Old value is not tombstone, > but remains until compaction. gc_grace_period is not related to this. > > > > Best regards, Vladimir Yudovin, > > > *Winguzone <https://winguzone.com?from=list> - Hosted Cloud Cassandra > Launch your cluster in minutes.* > > > > > > ---- On Mon, 14 Nov 2016 03:02:21 -0500*Lu, Boying <boying...@dell.com > <boying...@dell.com>>* wrote ---- > > > > Hi, All, > > > > Will the Cassandra generates a new tombstone when updating a column by > using CQL update statement? > > > > And is there any way to get the number of tombstones of a column family > since we want to void generating > > too many tombstones within gc_grace_period? > > > > Thanks > > > > Boying > > > > -- Close the World, Open the Net http://www.linux-wizard.net
