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https://issues.apache.org/jira/browse/HBASE-47?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12592873#action_12592873
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Andrew Purtell commented on HBASE-47:
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Please see attached patch "hbase-ttl-0.1.patch".
These items were easy:
- Add get and set TTL to HColumnDescriptor
- Change shell's CREATE TABLE statement so it takes a TTL parameter for column
families (and also ALTER TABLE, etc.)
- Compactor should screen out cells past TTL
This item was more involved due to memcache:
- Update HStore methods (get, put, etc) to check HStoreKey's timestamps against
TTL value when doing anything
I have done some simple testing and it works for me. I have not written a more
involved test case yet because there are two changes I had to make to Memcache
which might be not so nice, so maybe this is ok or maybe it needs more work or
some rethinking.
First, in order to enforce TTLs, Memcache has to be aware of them. I noticed
that effectively a Memcache is associated with a HStore, so I made the
association explicit by converting the Memcache constructor to accept a HStore
as the sole parameter. In this way Memcache can pick up TTLs from the
HColumnDescriptor associated with its associated HStore.
Second, I modified Memcache to discard cells with expired TTLs from the map.
Otherwise with short TTLs and small values maybe many hundreds or thousands of
expired cells may accumulate and need to be repeatedly and unnecessarily
iterated through for every getFull, or get, etc. But, due to how the code is
structured, currently expired cells may be dropped from both the memcache map
and the snapshot map. Possibly removing entries from the snapshot map violates
some assumptions made elsewhere. Avoiding this in my estimation would require
some refactoring.
> option to set TTL for columns in hbase
> --------------------------------------
>
> Key: HBASE-47
> URL: https://issues.apache.org/jira/browse/HBASE-47
> Project: Hadoop HBase
> Issue Type: New Feature
> Components: hql, regionserver
> Reporter: Billy Pearson
> Priority: Minor
>
> I would like to see the option to have a TTL on the columns in hbase this
> feature could be helpfully in removing stale data from large datasets with
> out havening to do a full scan of the dataset and then issuing deletes.
> Example
> Say I am crawling pages and only refreshing pages based on a set score and
> some pages doe not get updated over X days the old version of the page gets
> removed from the data set.
> Say I am striping out links form html and storing them say a link is removed
> from a page then I would need to issue a delete statement to remove that
> links form the data set with a ttl the link data would remove its self if not
> updated in x secs. These are just examples based on crawling like nutch but I
> can foresee many apps using this option.
> This is a feature in bigtables thats is handled when bigtable does
> garbage-collection.
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