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From Varun Sharma <va...@pinterest.com>
Subject Re: Get on a row with multiple columns
Date Sat, 09 Feb 2013 08:11:06 GMT
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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