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From Wei Tan <w...@us.ibm.com>
Subject Re: A general question on maxVersion handling when we have Secondary index tables
Date Tue, 28 Aug 2012 15:52:19 GMT
Thanks for sharing a pointer to your implementation. 
My two cents:
timestamp is a way to do MVCC and setting every KV with the same TS will 
get concurrency control very tricky and error prone, if not impossible
I think Ram is talking about the dead entry in the index table rather than 
data table. Deleting old index entries upfront when there is a new put 
might be a choice.

Best Regards,

Wei Tan 
Research Staff Member 
IBM T. J. Watson Research Center
19 Skyline Dr, Hawthorne, NY  10532
wtan@us.ibm.com; 914-784-6752

From:   Jesse Yates <jesse.k.yates@gmail.com>
To:     dev@hbase.apache.org, 
Date:   08/28/2012 04:00 AM
Subject:        Re: A general question on maxVersion handling when we have 
Secondary index tables


If I understand correctly, I think you can design your index such that you
don't actually use the timestamp (e.g. everything gets put with a TS = 10 
or some other non-special, relatively small number that's not 0 as I'd
worry about that in HBase ;) Then when you set maxVersions to 1, 
should be good.

You get a couple of wasted bytes from the TS, but with the prefixTrie 
that should be pretty minimal overhead. If you do need to keep track of 
timestamp you should be able to munge that back up into the column
qualifier (and just know that that last 64 bits is the timestamp). Again a
little more CPU cost, but its really not that big of an overhead. It seems
like you don't really care about the TS though, in which case this should
be pretty simple.

Out of curiosity, what are people using for their secondary indexing
solutions? I know there are a bunch out there, but don't know what people
have adopted, what they like/dislike, design tradeoffs made and why.

Disclaimer: I recently proposed a secondary indexing solution myself
(shameless self-plug:
and its something I'm working on for Salesforce - open sourced at some
point, promise!

Jesse Yates

On Tue, Aug 28, 2012 at 12:24 AM, Ramkrishna.S.Vasudevan <
ramkrishna.vasudevan@huawei.com> wrote:

> Hi All
> When we try to build any type of secondary indices for a given table how
> can
> one handle maxVersions in the secondary index tables.
> For eg,
> I have inserted
>  Row1  -  Val1  => t
> Row1 - Val2 => t+1
> Row1 - Val3. => t+2
> Ideally if my max versions is only one then Val3 should be my result If 
> query on main table for row1.
> Now in my index I will be having all the above 3 entries.  Now how can 
> remove the older entries from the index table that does not fit into
> maxVersions.
> Currently while scanning and the code that avoids the max Versions does 
> give any hooks to know the entries skipped thro versions.
> So any suggestions on this, I am still seeing the code for any other
> options
> but suggestions welcome.
> Regards
> Ram

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