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HBase, mail # dev - A general question on maxVersion handling when we have Secondary index tables

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RE: A general question on maxVersion handling when we have Secondary index tables
Ramkrishna.S.Vasudevan 2012-08-28, 08:51
Hi Jesse

Thanks lot for your reply.
-> Not maintaining timestamps in the sec index may cause problems when I
issue an delete on the main table and the corresponding things needs to be
deleted in the sec index.
-> As in the case I mentioned below
Index table will have
Val1_row1 (t)
Val2_row1 (t+2)
Val3_row1 (t+3)

Now my query says get me all the values greater than Val1 ideally only Val3
should be fetched.  But may be a direct scan on index table will not know he
should give me Val3_row3 alone.  Unless I know the number of existing
entries I will not be able to take a call as which one should be avoided and
which one to be considered. Any way on the main table for row1 only Val3
will be retrieved.

-> If I have a usecase like I will try to remove the older versions during
compaction of the index table how can we do it? Having all the older
versions also may lead to increase in the no of files and they may be
compacted.  But if I want to remove such olderversions during compaction
what can be the ways we can handle.  

These are some problems that come to my mind while we want to impl this.
Jesse, am I missing something here.  The prefixTrie stuff comes when we are
bothered about storage, yes using the prefixTrie stuff will help in storage.

And talking about the usage of sec index may be I cannot comment on that

> -----Original Message-----
> From: Jesse Yates [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, August 28, 2012 1:30 PM
> Subject: Re: A general question on maxVersion handling when we have
> Secondary index tables
> Ram,
> 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,
> everything
> should be good.
> You get a couple of wasted bytes from the TS, but with the prefixTrie
> stuff
> that should be pretty minimal overhead. If you do need to keep track of
> the
> 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:
> http://jyates.github.com/2012/07/09/consistent-enough-secondary-
> indexes.html)
> and its something I'm working on for Salesforce - open sourced at some
> point, promise!
> -Jesse
> -------------------
> Jesse Yates
> @jesse_yates
> jyates.github.com
> On Tue, Aug 28, 2012 at 12:24 AM, Ramkrishna.S.Vasudevan <
> > 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 I
> > query on main table for row1.
> >
> >
> >
> > Now in my index I will be having all the above 3 entries.  Now how
> can we
> > 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 not
> > 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.