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From yonghu <yongyong...@gmail.com>
Subject Re: What happened in hlog if data are deleted cuased by ttl?
Date Wed, 22 Aug 2012 08:19:08 GMT
I can fully understand normal deletion. But, in my point of view, ttl
deletion is different than the normal deletion. The insertion of ttl
data is recorded in hlog. But the ttl deletion is not recorded by
hlog. So, it failure occurs, should the ttl data be reinserted to data
or can we discard the certain ttl data? Moreover, ttl deletion is not
executed at data compaction time. Scanner needs to periodically scan
each Store file to execute deletion.



On Tue, Aug 21, 2012 at 5:29 PM, jmozah <jmozah@gmail.com> wrote:
> This helped me http://hadoop-hbase.blogspot.in/2011/12/deletion-in-hbase.html
> ./Zahoor
> HBase Musings
> On 14-Aug-2012, at 6:54 PM, Harsh J <harsh@cloudera.com> wrote:
>> Hi Yonghu,
>> A timestamp is stored along with each insert. The ttl is maintained at
>> the region-store level. Hence, when the log replays, all entries with
>> expired TTLs are automatically omitted.
>> Also, TTL deletions happen during compactions, and hence do not
>> carry/need Delete events. When scanning a store file, TTL-expired
>> entries are automatically skipped away.
>> On Tue, Aug 14, 2012 at 3:34 PM, yonghu <yongyong313@gmail.com> wrote:
>>> My hbase version is 0.92. I tried something as follows:
>>> 1.Created a table 'test' with 'course' in which ttl=5.
>>> 2. inserted one row into the table. 5 seconds later, the row was deleted.
>>> Later when I checked the log infor of 'test' table, I only found the
>>> inserted information but not deleted information.
>>> Can anyone tell me which information is written into hlog when data is
>>> deleted by ttl or in this situation, no information is written into
>>> the hlog. If there is no information of deletion in the log, how can
>>> we guarantee the data recovered by log are correct?
>>> Thanks!
>>> Yong
>> --
>> Harsh J

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