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 <st...@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
