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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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
> > > To: [EMAIL PROTECTED]
> > > 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 <[EMAIL PROTECTED]> 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