Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
HBase >> mail # user >> Use of MD5 as row keys - is this safe?


Copy link to this message
-
Re: Use of MD5 as row keys - is this safe?
Le 20/07/2012 18:22, Jonathan Bishop a écrit :
> Hi,
>
> I know it is a commonly suggested to use an MD5 checksum to create a row
> key from some other identifier, such as a string or long. This is usually
> done to guard against hot-spotting and seems to work well.
>
> My concern is that there no guard against collision when this is done - two
> different strings or longs could produce the same row-key. Although this is
> very unlikely, it is bothersome to consider this possibility for large
> systems.
>
> So what I usually do is concatenate the MD5 with the original identifier...
>
> MD5(id) + id
>
> which assures that the rowkey is both randomly distributed and unique.
>
> Is this necessary, or is it the common practice to just use the MD5
> checksum itself?
>
> Thanks,
>
> Jon

Hello Jonathan,

md5(id)+id is the good way to avoid hotspotting and insure uniqueness.

md5(id)[0]+id could be an other way to limit randomness of the rowid on
16 values
You can now combine (with OR logic) 16 filters in a scanner (on for each
letter available in md5 digest)
it limits the balance on 16 potentials regions olso.

Cheers,

--
Damien