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From "Stu Hood" <stu.h...@rackspace.com>
Subject Re: CASSANDRA-1472 (bitmap indexes)
Date Tue, 09 Nov 2010 18:05:24 GMT
Interesting, thanks for the info.

Perhaps the limitation is that index queries involving multiple clauses are currently implemented
using brute-force filtering rather than an index join? The bitmap indexes have native support
for this type of join, but it's not being used yet.

To confirm: have you tried the same scenario with KEYS indexes? They use the same codepath
for multiple index expressions, and should experience the same timeouts. Also, can you rerun
the KEYS_BITMAP test with DEBUG logging enabled, to ensure that we aren't going into some
kind of infinite loop?

Thanks for the help,
Stu

-----Original Message-----
From: "dragos cernahoschi" <dragos.cernahoschi@gmail.com>
Sent: Tuesday, November 9, 2010 11:50am
To: dev@cassandra.apache.org
Subject: Re: CASSANDRA-1472 (bitmap indexes)

I'm running the query on three columns with cardinalities: 22, 17 and 10.
Interesting, if combining columns with cardinalities:

22 + 17 => no exception
22 + 10 => no exception
10 + 17 => timed out exception
22 + 17 + 10 => timed out exception


On Tue, Nov 9, 2010 at 6:29 PM, Stu Hood <stu.hood@rackspace.com> wrote:

> Can you tell me a little bit about your key distribution? How many unique
> values are indexed (the cardinality)?
>
> Until the OrBiC projection I mention on 1472 is implemented, the bitmap
> secondary indexes will perform terribly for high cardinality datasets.
>
> Thanks!
>
>
> -----Original Message-----
> From: "dragos cernahoschi" <dragos.cernahoschi@gmail.com>
> Sent: Tuesday, November 9, 2010 10:14am
> To: dev@cassandra.apache.org
> Subject: Re: CASSANDRA-1472 (bitmap indexes)
>
> Meantime the number of SSTable(s) reduced to just 7. Initially the
> compaction thread suffered the same problem of "too many open files" and
> couldn't do any compaction.
>
> But I'm still not able to run my tests: TimedOutException :(
>
> On Tue, Nov 9, 2010 at 5:51 PM, Stu Hood <stu.hood@rackspace.com> wrote:
>
> > Hmm, 500 sstables is definitely a degenerate case: did you disable
> > compaction? By default, Cassandra strives to keep the sstable count below
> > ~32, since accesses to separate sstables require seeks.
> >
> > In this case, the query will seek 500 times to check the secondary index
> > for each sstable: if it finds matches it will need to seek to find them
> in
> > the primary index, and seek again for the data file.
> >
> > -----Original Message-----
> > From: "dragos cernahoschi" <dragos.cernahoschi@gmail.com>
> > Sent: Tuesday, November 9, 2010 5:33am
> > To: dev@cassandra.apache.org
> > Subject: Re: CASSANDRA-1472 (bitmap indexes)
> >
> > There are about 500 SSTables (12GB of data including index data,
> > statistics...) The source data file had about 3GB/26 million rows.
> >
> > I only test with EQ expressions for now.
> >
> > Increasing the file limit resolved the problem, but now I'm getting
> > TimedOutException(s) from thrift when "querying" even with slice size of
> 1.
> > Is my machine too small (core 2 duo 2.93 2GB RAM Ubuntu 10.04) for such a
> > test?
> >
> > I really have some interesting sets of data to test indexes with and I
> want
> > to make a comparison between ordinary indexes and bitmap indexes.
> >
> > Thank you,
> > Dragos
> >
> > On Mon, Nov 8, 2010 at 6:42 PM, Stu Hood <stu.hood@rackspace.com> wrote:
> >
> > > Dragos,
> > >
> > > How many SSTables did you have on disk, and were any of your index
> > > expressions GT(E)/LT(E)?
> > >
> > > I expect that you are bumping into a limitation of the current
> > > implementation: it opens up to 128 file-handles per SSTable in the
> worst
> > > case for a GT/LT query (one per index bucket).
> > >
> > > A future version might remove that requirement, but for now, you should
> > > probably bump the file handle limit on your machine to at least 2^16.
> > >
> > > Thanks,
> > > Stu
> > >
> > >
> > > -----Original Message-----
> > > From: "dragos cernahoschi" <dragos.cernahoschi@gmail.com>
> > > Sent: Monday, November 8, 2010 10:05am
> > > To: dev@cassandra.apache.org
> > > Subject: CASSANDRA-1472 (bitmap indexes)
> > >
> > > Hi,
> > >
> > > I've got an exception during the following test:
> > >
> > > test machine: core 2 duo 2.93 2GB RAM Ubuntu 10.04
> > >
> > > test scenario:
> > > - 1 column family
> > > - about 15 columns
> > > - 7 indexed columns (bitmap)
> > > - 26 million rows (insert operation went fine)
> > > - thrift "query" on 3 of the indexed columns with get_indexed_slices
> > > (count:
> > > 100)
> > > - got the following exception:
> > >
> > > 10/11/08 17:52:40 ERROR service.AbstractCassandraDaemon: Fatal
> exception
> > in
> > > thread Thread[ReadStage:3,5,main]
> > > java.io.IOError: java.io.FileNotFoundException:
> > > /home/dragos/cassandra/data/keyspace/visit-e-814-4-Bitidx.db (Too many
> > open
> > > files)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.bitidx.SegmentIterator.open(SegmentIterator.java:78)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.bitidx.BitmapIndexReader.openBin(BitmapIndexReader.java:226)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.bitidx.BitmapIndexReader.iterator(BitmapIndexReader.java:214)
> > >    at
> > >
> >
> org.apache.cassandra.io.sstable.SSTableReader.scan(SSTableReader.java:523)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.secindex.KeysBitmapIndex.iterator(KeysBitmapIndex.java:103)
> > >    at
> > >
> >
> org.apache.cassandra.db.ColumnFamilyStore.scan(ColumnFamilyStore.java:1371)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.service.IndexScanVerbHandler.doVerb(IndexScanVerbHandler.java:41)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.net.MessageDeliveryTask.run(MessageDeliveryTask.java:51)
> > >    at
> > >
> > >
> >
> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
> > >    at
> > >
> > >
> >
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
> > >    at java.lang.Thread.run(Thread.java:662)
> > > Caused by: java.io.FileNotFoundException:
> > > /home/dragos/cassandra/data/keyspace/visit-e-814-4-Bitidx.db (Too many
> > open
> > > files)
> > >    at java.io.FileInputStream.open(Native Method)
> > >    at java.io.FileInputStream.<init>(FileInputStream.java:106)
> > >    at
> > >
> org.apache.avro.file.SeekableFileInput.<init>(SeekableFileInput.java:29)
> > >    at
> org.apache.avro.file.DataFileReader.<init>(DataFileReader.java:38)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.bitidx.SegmentIterator.open(SegmentIterator.java:72)
> > >    ... 10 more
> > > 10/11/08 17:52:40 ERROR service.AbstractCassandraDaemon: Fatal
> exception
> > in
> > > thread Thread[ReadStage:2,5,main]
> > > java.io.IOError: java.io.FileNotFoundException:
> > > /home/dragos/cassandra/data/keyspace/visit-e-1018-Index.db (Too many
> open
> > > files)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.util.BufferedSegmentedFile.getSegment(BufferedSegmentedFile.java:68)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.util.SegmentedFile$SegmentIterator.next(SegmentedFile.java:129)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.util.SegmentedFile$SegmentIterator.next(SegmentedFile.java:1)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.SSTableReader.getPosition(SSTableReader.java:455)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.sstable.SSTableReader.getFileDataInput(SSTableReader.java:572)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.columniterator.SSTableSliceIterator.<init>(SSTableSliceIterator.java:49)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.filter.SliceQueryFilter.getSSTableColumnIterator(SliceQueryFilter.java:72)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.filter.QueryFilter.getSSTableColumnIterator(QueryFilter.java:84)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.ColumnFamilyStore.getTopLevelColumns(ColumnFamilyStore.java:1190)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(ColumnFamilyStore.java:1082)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(ColumnFamilyStore.java:1052)
> > >    at
> > >
> >
> org.apache.cassandra.db.ColumnFamilyStore.scan(ColumnFamilyStore.java:1378)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.service.IndexScanVerbHandler.doVerb(IndexScanVerbHandler.java:41)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.net.MessageDeliveryTask.run(MessageDeliveryTask.java:51)
> > >    at
> > >
> > >
> >
> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
> > >    at
> > >
> > >
> >
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
> > >    at java.lang.Thread.run(Thread.java:662)
> > > Caused by: java.io.FileNotFoundException:
> > > /home/dragos/cassandra/data/keyspace/visit-e-1018-Index.db (Too many
> open
> > > files)
> > >    at java.io.RandomAccessFile.open(Native Method)
> > >    at java.io.RandomAccessFile.<init>(RandomAccessFile.java:212)
> > >    at java.io.RandomAccessFile.<init>(RandomAccessFile.java:98)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.util.BufferedRandomAccessFile.<init>(BufferedRandomAccessFile.java:142)
> > >    at
> > >
> > >
> >
> org.apache.cassandra.io.util.BufferedSegmentedFile.getSegment(BufferedSegmentedFile.java:62)
> > >    ... 16 more
> > >
> > > The same test worked fine with 1 million rows.
> > >
> > >
> > >
> >
> >
> >
>
>
>



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