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From Varun Sharma <va...@pinterest.com>
Subject Re: Get on a row with multiple columns
Date Sat, 09 Feb 2013 08:05:33 GMT
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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