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HBase, mail # user - schema help


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Re: schema help
Rita 2011-08-25, 15:12
Thats very good to know.
I cant do the scan thru hbase shell?

On Thu, Aug 25, 2011 at 11:03 AM, Ian Varley <[EMAIL PROTECTED]> wrote:

> The rows don't need to be inserted in order; they're maintained in
> key-sorted order on the disk based on the architecture of HBase, which
> stores data sorted in memory and periodically flushes to immutable files in
> HDFS (which are later compacted to make read access more efficient). HBase
> keeps track of which physical files might contain a given key range, and
> only reads the ones it needs to.
>
> To do a query through the java API, you could create a scanner with a
> startrow that is the concatenation of your value for fieldA and the start
> time, and an endrow that has the current time.
>
> http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/Scan.html
>
> Ian
>
> On Aug 25, 2011, at 9:53 AM, Rita wrote:
>
> Thanks for your reponse.
>
> 30 million rows is the best case :-)
>
> Couple of questions about doing, [fieldA][time] as my key:
>  Would I have to insert in order?
>  If no, how would hbase know to stop scanning the entire table?
>  How would a query actually look like, if my key was [fieldA time]?
>
> As a matter of fact, I can do 100% of my queries. I will leave the 5% out
> of my project/schema.
>
>
> On Thu, Aug 25, 2011 at 10:13 AM, Ian Varley <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]>> wrote:
> Rita,
>
> There's no need to create separate tables here--the table is really just a
> "namespace" for keys. A better option would probably be having one table
> with "[fieldA][time]" (the two fields concatenated) as your row key. Then,
> you can seek directly to the start of your records in constant time, and
> then scan forward until you get to the end of the data (linear time in the
> size of data you expect to get back).
>
> The downside of this is that for the 5% of your queries that aren't in this
> form, you may have to do a full table scan. (Alternately, you could also
> maintain secondary indexes that help you get the data back with less than a
> full table scan; that would depend on the nature of the queries).
>
> In general, a good rule of thumb when designing a schema in HBase is, think
> first about how you'd ideally like to access the data. Then structure the
> data to match that access pattern. (This is obviously not ideal if you have
> lots of different access patterns, but then, that's what relational
> databases are for. Most commercial relational DBs wouldn't blink at doing
> analytical queries against 30 million rows.)
>
> Ian
>
> On Aug 25, 2011, at 9:03 AM, Rita wrote:
>
> Hello,
>
> I am trying to solve a time related problem. I can certainly use opentsdb
> for this but was wondering if anyone had a clever way to create this type
> of
> schema.
>
> I have an inventory table,
>
> time (unix epoch), fieldA, fieldB, data
>
>
> There are about 30 million of these entries.
>
> 95% of my queries will look like this:
> show me where fieldA=zCORE from range [1314180693 to now]
>
> for fieldA, there is a possibility of 4000 unique items.
> for fieldB, there is a possibility of 2 unique items (bool).
>
> So, I was thinking of creating 4000*2 tables and place the data like that
> so
> I can easly scan.
>
> Any thoughts about this? Will hbase freak out if i have 8000 tables?
>
>
>
>
>
>
> --
> --- Get your facts first, then you can distort them as you please.--
>
>
>
>
> --
> --- Get your facts first, then you can distort them as you please.--
>
>
--
--- Get your facts first, then you can distort them as you please.--