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From Arun Allamsetty <arun.allamse...@gmail.com>
Subject Re: How to limit columns returned by a single row in HBase
Date Sat, 19 Jul 2014 20:41:23 GMT

I have an idea which might be just bulloni, but people learn from mistakes
and this is my attempt to learn. So if I properly understand user use case,
you want to get the first 500 records pertaining to a file based on its
file name. Since you want to limit the number of records written, I won't
recommend writing each record as a column. But what if instead, we could
create a composite key consisting of the file name and the timestamp
(epoch) in a fashion similar to as described in Flurry - The Delicate Art
of Organizing Data in HBase <http://www.flurry.com/2012/06/12/137492485>.
If you want the latest timestamp first, we can use Long.MAX_VALUE -
timestamp in the constructor for the composite key. Now to get the top 500
records for, let's say, *fileA* and *2014/06/14*, convert the date to epoch
time and create an object of the composite key class you created. Create a
*Scan* object, specifying it as the start row and use
*Scan#setMaxResultSize* to 500. That should give you only the top 500
records and I believe the performance won't be bad provided you have the
hardware to manage your data volume.

Experts, please correct me wherever I am wrong.


On Sat, Jul 19, 2014 at 9:23 AM, SiMaYunRui <mylpis@hotmail.com> wrote:

> Hi experts,
> I have a wide-flat table, and during scan, how can I limit columns
> returned by a single row, instead of all rows (what ColumnCountGetFilter
> does)? Because I need to scan multiple rows at the same time, and in client
> side to do aggregation.
> Put more background, I am designing an auditing tools, which records
> pattern of “(who) operates against (what) at (when)”. The search pattern is
> like, given time range from "2014/6/14 13:45" to "2014/6/24 7:15", list all
> files (what part, start-with search) be operated in DESC order of (when).
> I have tens of millions of records per day, and keep them 30 - 90 days. So
> I am thinking about two designs: a) rowkey as (file name)_(reverse of
> when), problem is that people want to use start-wth search to match
> multiple files, in this way, scan has to go thru all matches files, which
> could be huge and then client has to re-order them to display 500 records
> on top; It could be very slow;
> b) use wide-flat table, rowkey as (file_name)_(reverse of when (unit to
> day to partition)). qualifier is (reverse of when). This design can
> leverage the fact that qualifiers are in order to make fewer search than #a
> in my personal opinion. But I cannot put all operations on a single file in
> one row, because total number might exceeds multiple millions.
> So I am thinking of grouping data into the following shape by using #b.
> Then back to my original question, because I only need 500 records, if the
> row (file A)_(2014/06/14), contains more than that number, can I stop it
> and then continue to scan next row? And if I already get enough in (file
> A)_(2014/06/14), can I skip (file A)_(2014/06/13) and then continue to scan
> (file B)_(2014/06/14) which is a different file?
> Row: (file A)_(2014/06/14)
>    d:1341069600 value
>    d:1341069500 value
>    d:1341069400 value
> Row: (file A)_(2014/06/13)
>    d:1341059600 value
>    d:1341059500 value
>    d:1341059400 value
> Row: (file B)_(2014/06/14)
>    d:1341069700 value
>    d:1341069580 value
>    d:1341069401 value
> 发自 Windows 邮件

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