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

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Use of MD5 as row keys - is this safe?

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

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?