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From Solvannan R M <solvanna...@zoho.com.INVALID>
Subject Re: HBase Scan consumes high cpu
Date Fri, 13 Sep 2019 13:29:32 GMT
Hi Anoop,

    We have executed the query with the qualifier set like you advised. 
But we dont get the results for the range but only the specified 
qualifier cell is returned.

Query & Result:

hbase(main):008:0> get 'mytable', 'MY_ROW', 
{COLUMN=>["pcf:\x00\x16\xDFx"], 
FILTER=>ColumnRangeFilter.new(Bytes.toBytes(1499000.to_java(:int)), 
true, Bytes.toBytes(1499010.to_java(:int)), false)}
COLUMN CELL
  pcf:\x00\x16\xDFx                 timestamp=1568380663616, 
value=\x00\x16\xDFx
1 row(s) in 0.0080 seconds

hbase(main):009:0>


Is there any other way to get arond this ?.


Regards,

Solvannan R M


On 2019/09/13 04:53:45, Anoop John wrote:
 > Hi>
 > When you did a put with a lower qualifier int (put 'mytable',>
 > 'MY_ROW', "pcf:\x0A", "\x00") the system flow is getting a valid cell 
at>
 > 1st step itself and that getting passed to the Filter. The Filter is 
doing>
 > a seek which just avoids all the in between deletes and puts 
processing..>
 > In 1st case the Filter wont get into action at all unless the scan flow>
 > sees a valid cell. The delete processing happens as 1st step before the>
 > filter processinf step happening.>
 >
 > In this case I am wondering why you can not add the specific 1st 
qualifier>
 > in the get part itself along with the column range filter. I mean>
 >
 > get 'mytable', 'MY_ROW', {COLUMN=>['pcf: *1499000 * '],>
 > FILTER=>ColumnRangeFilter.new(Bytes.toBytes(1499000.to_java(:int)),>
 > true, Bytes.toBytes(1499010.to_java(:int)), false)}>
 >
 > Pardon the syntax it might not be proper for the shell.. Can this be 
done?>
 > This will make the scan to make a seek to the given qualifier at 1st 
step>
 > itself.>
 >
 > Anoop>
 >
 > On Thu, Sep 12, 2019 at 10:18 PM Udai Bhan Kashyap (BLOOMBERG/ 
PRINCETON) <>
 > ukashyap1@bloomberg.net> wrote:>
 >
 > > Are you keeping the deleted cells? Check 'VERSIONS' for the column 
family>
 > > and set it to 1 if you don't want to keep the deleted cells.>
 > >>
 > > From: user@hbase.apache.org At: 09/12/19 12:40:01To:>
 > > user@hbase.apache.org>
 > > Subject: Re: HBase Scan consumes high cpu>
 > >>
 > > Hi,>
 > >>
 > > As said earlier, we have populated the rowkey "MY_ROW" with integers>
 > > from 0 to 1500000 as column qualifiers. Then we have deleted the>
 > > qualifiers from 0 to 1499000.>
 > >>
 > > We executed the following query. It took 15.3750 seconds to execute.>
 > >>
 > > hbase(main):057:0> get 'mytable', 'MY_ROW', {COLUMN=>['pcf'],>
 > > FILTER=>ColumnRangeFilter.new(Bytes.toBytes(1499000.to_java(:int)),>
 > > true, Bytes.toBytes(1499010.to_java(:int)), false)}>
 > > COLUMN CELL>
 > > pcf:\x00\x16\xDFx timestamp=1568123881899,>
 > > value=\x00\x16\xDFx>
 > > pcf:\x00\x16\xDFy timestamp=1568123881899,>
 > > value=\x00\x16\xDFy>
 > > pcf:\x00\x16\xDFz timestamp=1568123881899,>
 > > value=\x00\x16\xDFz>
 > > pcf:\x00\x16\xDF{ timestamp=1568123881899,>
 > > value=\x00\x16\xDF{>
 > > pcf:\x00\x16\xDF| timestamp=1568123881899,>
 > > value=\x00\x16\xDF|>
 > > pcf:\x00\x16\xDF} timestamp=1568123881899,>
 > > value=\x00\x16\xDF}>
 > > pcf:\x00\x16\xDF~ timestamp=1568123881899,>
 > > value=\x00\x16\xDF~>
 > > pcf:\x00\x16\xDF\x7F timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x7F>
 > > pcf:\x00\x16\xDF\x80 timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x80>
 > > pcf:\x00\x16\xDF\x81 timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x81>
 > > 1 row(s) in 15.3750 seconds>
 > >>
 > >>
 > > Now we inserted a new column with qualifier 10 (\x0A), such that it>
 > > comes earlier in lexicographical order. Now we executed the same 
query.>
 > > It only took 0.0240 seconds.>
 > >>
 > > hbase(main):058:0> put 'mytable', 'MY_ROW', "pcf:\x0A", "\x00">
 > > 0 row(s) in 0.0150 seconds>
 > > hbase(main):059:0> get 'mytable', 'MY_ROW', {COLUMN=>['pcf'],>
 > > FILTER=>ColumnRangeFilter.new(Bytes.toBytes(1499000.to_java(:int)),>
 > > true, Bytes.toBytes(1499010.to_java(:int)), false)}>
 > > COLUMN CELL>
 > > pcf:\x00\x16\xDFx timestamp=1568123881899,>
 > > value=\x00\x16\xDFx>
 > > pcf:\x00\x16\xDFy timestamp=1568123881899,>
 > > value=\x00\x16\xDFy>
 > > pcf:\x00\x16\xDFz timestamp=1568123881899,>
 > > value=\x00\x16\xDFz>
 > > pcf:\x00\x16\xDF{ timestamp=1568123881899,>
 > > value=\x00\x16\xDF{>
 > > pcf:\x00\x16\xDF| timestamp=1568123881899,>
 > > value=\x00\x16\xDF|>
 > > pcf:\x00\x16\xDF} timestamp=1568123881899,>
 > > value=\x00\x16\xDF}>
 > > pcf:\x00\x16\xDF~ timestamp=1568123881899,>
 > > value=\x00\x16\xDF~>
 > > pcf:\x00\x16\xDF\x7F timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x7F>
 > > pcf:\x00\x16\xDF\x80 timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x80>
 > > pcf:\x00\x16\xDF\x81 timestamp=1568123881899,>
 > > value=\x00\x16\xDF\x81>
 > > 1 row(s) in 0.0240 seconds>
 > > hbase(main):060:0>>
 > >>
 > >>
 > > We were able to reproduce the result consistently same, the pattern>
 > > being bulk insert followed by bulk delete of most of the earlier 
columns.>
 > >>
 > >>
 > > We observed the following behaviour while debugging the StoreScanner>
 > > (regionserver).>
 > >>
 > > Case 1:>
 > >>
 > > 1. When StoreScanner.next() is called, it starts to iterate over the>
 > > cells from the start of the rowkey.>
 > >>
 > > 2. As all the cells are deleted (from 0 to 1499000), we could see>
 > > alternate delete and put type cells. Now, the>
 > > NormalUserScanQueryMatcher.match() returns>
 > > ScanQueryMatcher.MatchCode.SKIP and>
 > > ScanQueryMatcher.MatchCode.SEEK_NEXT_COL for Delete and Put type cell>
 > > respectively. This iteration happens throughout the range of 0 to 
1499000.>
 > >>
 > > 3. This happens until a valid Put type cell is encountered, where the>
 > > matcher applies the ColumnRangeFilter to the cell, which in turm 
returns>
 > > ScanQueryMatcher.MatchCode.SEEK_NEXT_USING_HINT. In the next 
iteration>
 > > it seeks directly to the desired column.>
 > >>
 > >>
 > > Case 2:>
 > >>
 > > 1. When StoreScanner.next() is called, it starts to iterate over the>
 > > cells from the start of the rowkey.>
 > >>
 > > 2. When the Put cell of qualifier 10 (\x0A) is encountered, the 
matcher>
 > > returns ScanQueryMatcher.MatchCode.SEEK_NEXT_USING_HINT. In the next>
 > > iteration it seeks directly to the desired column.>
 > >>
 > >>
 > > Please let us know if this behaviour is intentional or it could be 
avoided.>
 > >>
 > > Regards,>
 > >>
 > > Solvannan R M>
 > >>
 > >>
 > > On 2019/09/10 17:12:36, Josh Elser wrote:>
 > > > Deletes are held in memory. They represent data you have to 
traverse >>
 > > > until that data is flushed out to disk. When you write a new cell>
 > > with a >>
 > > > qualifier of 10, that sorts, lexicographically, "early" with 
respect>
 > > to >>
 > > > the other qualifiers you've written.>>
 > > >>
 > > > By that measure, if you are only scanning for the first column in 
this >>
 > > > row which you've loaded with deletes, it would make total sense 
to me >>
 > > > that the first case is slow and the second fast is fast>>
 > > >>
 > > > Can you please share exactly how you execute your "query" for>
 > > both(all) >>
 > > > scenarios?>>
 > > >>
 > > > On 9/10/19 11:35 AM, Solvannan R M wrote:>>
 > > > > Hi,>>
 > > > > >>
 > > > > We have been using HBase (1.4.9) for a case where timeseries data>
 > > is continuously inserted and deleted (high churn) against a single>
 > > rowkey. The column keys would represent timestamp more or less. 
When we>
 > > scan this data using ColumnRangeFilter for a recent time-range, 
scanner>
 > > for the stores (memstore & storefiles) has to go through contiguous>
 > > deletes, before it reaches the requested timerange data. While using>
 > > this scan, we could notice 100% cpu usages in single core by the>
 > > regionserver process.>>
 > > > > >>
 > > > > So, for our case, most of the cells with older timestamps will be>
 > > in deleted state. While traversing these deleted cells, the 
regionserver>
 > > process causing 100% cpu usage in single core.>>
 > > > > >>
 > > > > We tried to trace the code for scan and we observed the following>
 > > behaviour.>>
 > > > > >>
 > > > > 1. While scanner is initialized, it seeked all the store-scanners>
 > > to the start of the rowkey.>>
 > > > > 2. Then it traverses the deleted cells and discards it (as it was>
 > > deleted) one by one.>>
 > > > > 3. When it encounters a valid cell (put type), it applies the>
 > > filter and it returns SEEK_TO_NEXT_USING_HINT.>>
 > > > > 4. Now the scanner seeks to the required key directly and 
returning>
 > > the results quickly then.>>
 > > > > >>
 > > > > For confirming the mentioned behaviour, we have done a test:>>
 > > > > 1. We have populated a single rowkey with column qualifier as a>
 > > range of integers of 0 to 1500000 with random data.>>
 > > > > 2. We then deleted the column qualifier range of 0 to 1499000.>>
 > > > > 3. Now the data is only in memsore. No store file exists.>>
 > > > > 4. Now we scanned the rowkey with ColumnRangeFilter[1499000,>
 > > 1499010).>>
 > > > > 5. The query took 12 seconds to execute. During this query, a>
 > > single core is completely used>>
 > > > > 6. Then we put a new cell with qualifier 10.>>
 > > > > 7. Executed the same query, it took 0.018 seconds to execute.>>
 > > > > >>
 > > > > Kindly check this and advise !.>>
 > > > > >>
 > > > > Regards,>>
 > > > > Solvannan R M>>
 > > > > >>
 > > >>
 > >>
 > >>
 > >>
 >

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