hadoop-common-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Per Steffensen <st...@designware.dk>
Subject Re: Routing and region deletes
Date Thu, 08 Dec 2011 14:41:42 GMT
Thanks for your reply!

Michel Segel skrev:
> Per Seffensen,
> I would urge you to step away from the keyboard and rethink your design.
Will do :-) But would actually still like to receive answers for my 
questions - just pretend that my ideas are not so stupid and let me know 
if it can be done
> It sounds like you want to replicate a date partition model similar to what you would
do if you were attempting this with HBase.
> HBase is not a relational database and you have a different way of doing things.
I know
> You could put the date/time stamp in the key such that your data is sorted by date.
But I guess that would not guarantee that records with timestamps from a 
specific day or month all exist in the same set of regions and that 
records with timestamps from other days or months all exist outside 
those regions, so that I can delete records from that day or month, just 
by deleting the regions.
> However, this would cause hot spots.  Think about how you access the data. It sounds
like you access the more recent data more frequently than historical data.
Not necessarily wrt reading, but certainly I (almost) only write new 
records with timestamps from the current day/month.
>   This is a bad idea in HBase.
> (note: it may still make sense to do this ... You have to think more about the data and
consider alternatives.)
> I personally would hash the key for even distribution, again depending on the data access
pattern.  (hashed data means you can't do range queries but again, it depends on what you
are doing...)
> You also have to think about how you purge the data. You don't just drop a region.
I know that this is not the "default" way of deleting data, but it is 
possible? Believe a region is basically just a folder with a set of 
files and deleting those would be a matter of a few ms. So if I can 
route all records with timestamps from a certain day or month to a 
designated set of regions, deleting all those records will be a matter 
of deleting #regions-in-that-set folders on disk - very quick. The 
alternative is to do 50mio+ single delete operations every day (or 1,5 
billion operations every month), and that will not even free up space 
immediately since the records will actually just be marked deleted (in a 
new file) - space will not be freed before next compaction of the 
involved regions (see e.g. http://outerthought.org/blog/465-ot.html).
>  Doing a full table scan once a month to delete may not be a bad thing.
But I dont believe one full table scan will be enough. For that to be 
possible, at least I would have to be able to provide HBase with all 1,5 
billion records to delete in one "delete"-call - thats probably not 
possible :-)
>  Again it depends on what you are doing...
> Just my opinion. Others will have their own... Now I'm stepping away from the keyboard
to get my morning coffee...
Enjoy. Then I will consider leaving work (its late afternoon in Europe)
> :-)
> Sent from a remote device. Please excuse any typos...
> Mike Segel
> On Dec 8, 2011, at 7:13 AM, Per Steffensen <steff@designware.dk> wrote:
>> Hi
>> The system we are going to work on will receive 50mio+ new datarecords every day.
We need to keep a history of 2 years of data (thats 35+ billion datarecords in the storage
all in all), and that basically means that we also need to delete 50mio+ datarecords every
day, or e.g. 1,5 billion every month. We plan to store the datarecords in HBase.
>> Is it somehow possible to tell HBase to put (route) all datarecords belonging to
a specific date or month to a designated set of regions (and route nothing else there), so
that deleting all data belonging to that day/month i basically deleting those regions entirely?
And is explicit deletion of entire regions possible at all?
>> The reason I want to do this is that I expect it to be much faster than doing explicit
deletion record by record of 50mio+ records every day.
>> Regards, Per Steffensen

  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message