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HBase >> mail # user >> Re: HBase - Secondary Index


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RE: HBase - Secondary Index
Hi Anil,

>1. In your presentation you mentioned that region of Primary Table and
Region of Secondary Table are always located on the same region server. How
do you achieve it? By using the Primary table rowkey as prefix of  Rowkey
of Secondary Table? Will your implementation work if the rowkey of primary
table cannot be used as prefix in rowkey of Secondary table( i have this
limitation in my use case)?
First all there will be same number of regions in both primary and index tables. All the start/stop keys of the regions also will be same.
Suppose there are 2 regions on main table say for keys 0-10 and 10-20.  Then we will create 2 regions in index table also with same key ranges.
At the master balancing level it is easy to collocate these regions seeing the start and end keys.
When the selection of the rowkey that will be used in the index table is the key here.
What we will do is all the rowkeys in the index table will be prefixed with the start key of the region/
When an entry is added to the main table with rowkey as 5 it will go to the 1st region (0-10)
Now there will be index region with range as 0-10.  We will select this region to store this index data.
The row getting added into the index region for this entry will have a rowkey 0_x_5
I am just using '_' as a seperator here just to show this. Actually we wont be having any seperator.
So the rowkeys (in index region) will have a static begin part always.  Will scan time also we know this part and so the startrow and endrow creation for the scan will be possible.. Note that we will store the actual table row key as the last part of the index rowkey itself not as a value.
This is better option in our case of handling the scan index usage also at sever side.  There is no index data fetch to client side..

I feel your use case perfectly fit with our model

>2. Are you using an Endpoint or Observer for building the secondary index
table?
Observer

>3. "Custom balancer do collocation". Is it a custom load balancer of HBase
Master or something else?
It is a balancer implementation which will be plugged into Master

>4. Your region split looks interesting. I dont have much info about it. Can
you point to some docs on IndexHalfStoreFileReader?
Sorry I am not able to publish any design doc or code as the company has not decided to open src the solution yet.
Any particular query you come acorss pls feel free to aske me :)
You can see the HalfStoreFileReader class 1st..

-Anoop-
________________________________________
From: anil gupta [[EMAIL PROTECTED]]
Sent: Friday, December 14, 2012 2:11 PM
To: [EMAIL PROTECTED]
Subject: Re: HBase - Secondary Index

Hi Anoop,

Nice presentation and seems like a smart implementation. Since the
presentation only covered bullet points so i have couple of questions on
your implementation. :)

Here is a recap to my implementation and our previous discussion on
Secondary index:

Here is the link to previous email thread:
http://search-hadoop.com/m/1zWPMaaRtr .

The secondary index is stored in table "B" as rowkey B --> family:<rowkey
A>  . "<rowkey A>" is the column qualifier. Every row in B will only on
have one column "k" and the value of that column is the rowkey of A.

Suppose i am storing customer events in table A. I have two requirement for
data query:
1. Query customer events on basis of customer_Id and event_ID.
2. Query customer events on basis of event_timestamp and customer_ID.

70% of querying is done by query#1, so i will create
<customer_Id><event_ID> as row key of Table A.
Now, in order to support fast results for query#2, i need to create a
secondary index on A. I store that secondary index in B, rowkey of B is
<event_timestamp><customer_ID>.Every row stores the corresponding rowkey of
A.

HBase Querying approach:
1. Scan the secondary table by using prefix filter and startRow to get the
list of Rowkeys of Primary table.
2. Do a batch get on primary table by using HTable.get(List<Get>) method
using the list of Rowkeys obtained in step1.

The only issue is that in my solution i have at least two RPC calls. Once
each in step1 and step2 above. I want to reduce the number of RPC to 1 if
possible.
******Questions on your implementation:*********

1. In your presentation you mentioned that region of Primary Table and
Region of Secondary Table are always located on the same region server. How
do you achieve it? By using the Primary table rowkey as prefix of  Rowkey
of Secondary Table? Will your implementation work if the rowkey of primary
table cannot be used as prefix in rowkey of Secondary table( i have this
limitation in my use case)?
2. Are you using an Endpoint or Observer for building the secondary index
table?
3. "Custom balancer do collocation". Is it a custom load balancer of HBase
Master or something else?
4. Your region split looks interesting. I dont have much info about it. Can
you point to some docs on IndexHalfStoreFileReader?

Thanks,
Anil Gupta

On Tue, Dec 4, 2012 at 12:10 AM, Anoop Sam John <[EMAIL PROTECTED]> wrote:
Thanks & Regards,
Anil Gupta
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB