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From Varun Sharma <va...@pinterest.com>
Subject Re: Get on a row with multiple columns
Date Sat, 09 Feb 2013 08:29:01 GMT
Yeah, I meant true...

On Sat, Feb 9, 2013 at 12:17 AM, lars hofhansl <larsh@apache.org> wrote:

> Should be set to true. If tcpnodelay is set to true, Nagle's is disabled.
>
> -- Lars
>
>
>
> ________________________________
>  From: Varun Sharma <varun@pinterest.com>
> To: user@hbase.apache.org; lars hofhansl <larsh@apache.org>
> Sent: Saturday, February 9, 2013 12:11 AM
> Subject: Re: Get on a row with multiple columns
>
>
> Okay I did my research - these need to be set to false. I agree.
>
>
> On Sat, Feb 9, 2013 at 12:05 AM, Varun Sharma <varun@pinterest.com> wrote:
>
> I have ipc.client.tcpnodelay, ipc.server.tcpnodelay set to false and the
> hbase one - [hbase].ipc.client.tcpnodelay set to true. Do these induce
> network latency ?
> >
> >
> >On Fri, Feb 8, 2013 at 11:57 PM, lars hofhansl <larsh@apache.org> wrote:
> >
> >Sorry.. I meant set these two config parameters to true (not false as I
> state below).
> >>
> >>
> >>
> >>
> >>----- Original Message -----
> >>From: lars hofhansl <larsh@apache.org>
> >>To: "user@hbase.apache.org" <user@hbase.apache.org>
> >>Cc:
> >>Sent: Friday, February 8, 2013 11:41 PM
> >>Subject: Re: Get on a row with multiple columns
> >>
> >>Only somewhat related. Seeing the magic 40ms random read time there. Did
> you disable Nagle's?
> >>(set hbase.ipc.client.tcpnodelay and ipc.server.tcpnodelay to false in
> hbase-site.xml).
> >>
> >>________________________________
> >>From: Varun Sharma <varun@pinterest.com>
> >>To: user@hbase.apache.org; lars hofhansl <larsh@apache.org>
> >>Sent: Friday, February 8, 2013 10:45 PM
> >>Subject: Re: Get on a row with multiple columns
> >>
> >>The use case is like your twitter feed. Tweets from people u follow. When
> >>someone unfollows, you need to delete a bunch of his tweets from the
> >>following feed. So, its frequent, and we are essentially running into
> some
> >>extreme corner cases like the one above. We need high write throughput
> for
> >>this, since when someone tweets, we need to fanout the tweet to all the
> >>followers. We need the ability to do fast deletes (unfollow) and fast
> adds
> >>(follow) and also be able to do fast random gets - when a real user loads
> >>the feed. I doubt we will able to play much with the schema here since we
> >>need to support a bunch of use cases.
> >>
> >>@lars: It does not take 30 seconds to place 300 delete markers. It takes
> 30
> >>seconds to first find which of those 300 pins are in the set of columns
> >>present - this invokes 300 gets and then place the appropriate delete
> >>markers. Note that we can have tens of thousands of columns in a single
> row
> >>so a single get is not cheap.
> >>
> >>If we were to just place delete markers, that is very fast. But when
> >>started doing that, our random read performance suffered because of too
> >>many delete markers. The 90th percentile on random reads shot up from 40
> >>milliseconds to 150 milliseconds, which is not acceptable for our
> usecase.
> >>
> >>Thanks
> >>Varun
> >>
> >>On Fri, Feb 8, 2013 at 10:33 PM, lars hofhansl <larsh@apache.org> wrote:
> >>
> >>> Can you organize your columns and then delete by column family?
> >>>
> >>> deleteColumn without specifying a TS is expensive, since HBase first
> has
> >>> to figure out what the latest TS is.
> >>>
> >>> Should be better in 0.94.1 or later since deletes are batched like Puts
> >>> (still need to retrieve the latest version, though).
> >>>
> >>> In 0.94.3 or later you can also the BulkDeleteEndPoint, which basically
> >>> let's specify a scan condition and then place specific delete marker
> for
> >>> all KVs encountered.
> >>>
> >>>
> >>> If you wanted to get really
> >>> fancy, you could hook up a coprocessor to the compaction process and
> >>> simply filter all KVs you no longer want (without ever placing any
> >>> delete markers).
> >>>
> >>>
> >>> Are you saying it takes 15 seconds to place 300 version delete
> markers?!
> >>>
> >>>
> >>> -- Lars
> >>>
> >>>
> >>>
> >>> ________________________________
> >>>  From: Varun Sharma <varun@pinterest.com>
> >>> To: user@hbase.apache.org
> >>> Sent: Friday, February 8, 2013 10:05 PM
> >>> Subject: Re: Get on a row with multiple columns
> >>>
> >>> We are given a set of 300 columns to delete. I tested two cases:
> >>>
> >>> 1) deleteColumns() - with the 's'
> >>>
> >>> This function simply adds delete markers for 300 columns, in our case,
> >>> typically only a fraction of these columns are actually present - 10.
> After
> >>> starting to use deleteColumns, we starting seeing a drop in cluster
> wide
> >>> random read performance - 90th percentile latency worsened, so did 99th
> >>> probably because of having to traverse delete markers. I attribute
> this to
> >>> profusion of delete markers in the cluster. Major compactions slowed
> down
> >>> by almost 50 percent probably because of having to clean out
> significantly
> >>> more delete markers.
> >>>
> >>> 2) deleteColumn()
> >>>
> >>> Ended up with untolerable 15 second calls, which clogged all the
> handlers.
> >>> Making the cluster pretty much unresponsive.
> >>>
> >>> On Fri, Feb 8, 2013 at 9:55 PM, Ted Yu <yuzhihong@gmail.com> wrote:
> >>>
> >>> > For the 300 column deletes, can you show us how the Delete(s) are
> >>> > constructed ?
> >>> >
> >>> > Do you use this method ?
> >>> >
> >>> >   public Delete deleteColumns(byte [] family, byte [] qualifier) {
> >>> > Thanks
> >>> >
> >>> > On Fri, Feb 8, 2013 at 9:44 PM, Varun Sharma <varun@pinterest.com>
> >>> wrote:
> >>> >
> >>> > > So a Get call with multiple columns on a single row should be
much
> >>> faster
> >>> > > than independent Get(s) on each of those columns for that row.
I am
> >>> > > basically seeing severely poor performance (~ 15 seconds) for
> certain
> >>> > > deleteColumn() calls and I am seeing that there is a
> >>> > > prepareDeleteTimestamps() function in HRegion.java which first
> tries to
> >>> > > locate the column by doing individual gets on each column you
want
> to
> >>> > > delete (I am doing 300 column deletes). Now, I think this should
> ideall
> >>> > by
> >>> > > 1 get call with the batch of 300 columns so that one scan can
> retrieve
> >>> > the
> >>> > > columns and the columns that are found, are indeed deleted.
> >>> > >
> >>> > > Before I try this fix, I wanted to get an opinion if it will make
a
> >>> > > difference to batch the get() and it seems from your answer, it
> should.
> >>> > >
> >>> > > On Fri, Feb 8, 2013 at 9:34 PM, lars hofhansl <larsh@apache.org>
> >>> wrote:
> >>> > >
> >>> > > > Everything is stored as a KeyValue in HBase.
> >>> > > > The Key part of a KeyValue contains the row key, column family,
> >>> column
> >>> > > > name, and timestamp in that order.
> >>> > > > Each column family has it's own store and store files.
> >>> > > >
> >>> > > > So in a nutshell a get is executed by starting a scan at
the row
> key
> >>> > > > (which is a prefix of the key) in each store (CF) and then
> scanning
> >>> > > forward
> >>> > > > in each store until the next row key is reached. (in reality
it
> is a
> >>> > bit
> >>> > > > more complicated due to multiple versions, skipping columns,
etc)
> >>> > > >
> >>> > > >
> >>> > > > -- Lars
> >>> > > > ________________________________
> >>> > > > From: Varun Sharma <varun@pinterest.com>
> >>> > > > To: user@hbase.apache.org
> >>> > > > Sent: Friday, February 8, 2013 9:22 PM
> >>> > > > Subject: Re: Get on a row with multiple columns
> >>> > > >
> >>> > > > Sorry, I was a little unclear with my question.
> >>> > > >
> >>> > > > Lets say you have
> >>> > > >
> >>> > > > Get get = new Get(row)
> >>> > > > get.addColumn("1");
> >>> > > > get.addColumn("2");
> >>> > > > .
> >>> > > > .
> >>> > > > .
> >>> > > >
> >>> > > > When internally hbase executes the batch get, it will seek
to
> column
> >>> > "1",
> >>> > > > now since data is lexicographically sorted, it does not need
to
> seek
> >>> > from
> >>> > > > the beginning to get to "2", it can continue seeking, henceforth
> >>> since
> >>> > > > column "2" will always be after column "1". I want to know
> whether
> >>> this
> >>> > > is
> >>> > > > how a multicolumn get on a row works or not.
> >>> > > >
> >>> > > > Thanks
> >>> > > > Varun
> >>> > > >
> >>> > > > On Fri, Feb 8, 2013 at 9:08 PM, Marcos Ortiz <mlortiz@uci.cu>
> wrote:
> >>> > > >
> >>> > > > > Like Ishan said, a get give an instance of the Result
class.
> >>> > > > > All utility methods that you can use are:
> >>> > > > >  byte[] getValue(byte[] family, byte[] qualifier)
> >>> > > > >  byte[] value()
> >>> > > > >  byte[] getRow()
> >>> > > > >  int size()
> >>> > > > >  boolean isEmpty()
> >>> > > > >  KeyValue[] raw() # Like Ishan said, all data here is
sorted
> >>> > > > >  List<KeyValue> list()
> >>> > > > >
> >>> > > > >
> >>> > > > >
> >>> > > > >
> >>> > > > > On 02/08/2013 11:29 PM, Ishan Chhabra wrote:
> >>> > > > >
> >>> > > > >> Based on what I read in Lars' book, a get will return
a
> result a
> >>> > > Result,
> >>> > > > >> which is internally a KeyValue[]. This KeyValue[]
is sorted
> by the
> >>> > key
> >>> > > > and
> >>> > > > >> you access this array using raw or list methods
on the Result
> >>> > object.
> >>> > > > >>
> >>> > > > >>
> >>> > > > >> On Fri, Feb 8, 2013 at 5:40 PM, Varun Sharma <
> varun@pinterest.com
> >>> >
> >>> > > > wrote:
> >>> > > > >>
> >>> > > > >>  +user
> >>> > > > >>>
> >>> > > > >>> On Fri, Feb 8, 2013 at 5:38 PM, Varun Sharma
<
> >>> varun@pinterest.com>
> >>> > > > >>> wrote:
> >>> > > > >>>
> >>> > > > >>>  Hi,
> >>> > > > >>>>
> >>> > > > >>>> When I do a Get on a row with multiple column
qualifiers.
> Do we
> >>> > sort
> >>> > > > the
> >>> > > > >>>> column qualifers and make use of the sorted
order when we
> get
> >>> the
> >>> > > > >>>>
> >>> > > > >>> results ?
> >>> > > > >>>
> >>> > > > >>>> Thanks
> >>> > > > >>>> Varun
> >>> > > > >>>>
> >>> > > > >>>>
> >>> > > > >>
> >>> > > > >>
> >>> > > > > --
> >>> > > > > Marcos Ortiz Valmaseda,
> >>> > > > > Product Manager && Data Scientist at UCI
> >>> > > > > Blog: http://marcosluis2186.**posterous.com<
> >>> > > > http://marcosluis2186.posterous.com>
> >>> > > > > Twitter: @marcosluis2186 <http://twitter.com/**marcosluis2186<
> >>> > > > http://twitter.com/marcosluis2186>
> >>> > > > > >
> >>> > > > >
> >>> > > >
> >>> > >
> >>> >
> >>>
> >>
> >>
> >
>

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