Re: False positive increasing

[Ariel Weisberg]

Jeff is probably correct. I skimmed over the fact that it's just
increasing by one every few minutes so I went on about a different
scenario.

On Mon, Jul 3, 2017, at 01:46 PM, Jeff Jirsa wrote:
> 
> 
> On 2017-07-03 06:55 (-0700), Jean Carlo 
> wrote: 
> > Hello
> > 
> > Lately I am observing that the false positives of one of my nodes are
> > increasing in a continous way (1 per 5min)
> > 
> 
> There's probably one partition that has a false positive entry, and you
> read it once every 5 minutes. Bloom filters are probabilistic, false
> positives are OK, it just causes a little bit of extra disk IO. 
> 
> > Bloom filter false positives: 532
> > Bloom filter false ratio: 0.01449
> > Bloom filter space used: 1.34 MB
> > Bloom filter off heap memory used: 1.33 MB
> > 
> > At the same time I can see that the duration of GC has increased also
> > 
> > There is a link between the increasment of the GC and the bloom filter ?
> > 
> 
> Probably not in any meaningful way (like mentioned above, false positive
> causes some extra disk IO to check one extra sstable, but it's not going
> to really impact GC in any meaningful way if it's truly a false
> positive).
> 
> 
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Re: False positive increasing

[Jeff Jirsa]

On 2017-07-03 06:55 (-0700), Jean Carlo  wrote: 
> Hello
> 
> Lately I am observing that the false positives of one of my nodes are
> increasing in a continous way (1 per 5min)
> 

There's probably one partition that has a false positive entry, and you read it 
once every 5 minutes. Bloom filters are probabilistic, false positives are OK, 
it just causes a little bit of extra disk IO. 

> Bloom filter false positives: 532
> Bloom filter false ratio: 0.01449
> Bloom filter space used: 1.34 MB
> Bloom filter off heap memory used: 1.33 MB
> 
> At the same time I can see that the duration of GC has increased also
> 
> There is a link between the increasment of the GC and the bloom filter ?
> 

Probably not in any meaningful way (like mentioned above, false positive causes 
some extra disk IO to check one extra sstable, but it's not going to really 
impact GC in any meaningful way if it's truly a false positive).


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Re: False positive increasing

[Ariel Weisberg]

Hi,

The number of false positives may be increasing because more filters are
being consulted on each query. The number of filters consulted on each
query is a function of number of sstables consulted.
You may be seeing an increase in number of tables consulted if
compaction is falling behind. I'm not an expert on the operational
playbook for compaction falling behind, but you can change the
compaction throttle, disable gossip so compaction can catch up (this can
go wrong), add capacity by adding nodes.
If it's just one node you may also want to look into why that node
is a hot spot. Is there a single large partition that could be
causing issues?
Ariel

On Mon, Jul 3, 2017, at 09:55 AM, Jean Carlo wrote:
> Hello
> Lately I am observing that the false positives of one of my nodes are
> increasing in a continous way (1 per 5min)> 
> Bloom filter false positives: 532
> Bloom filter false ratio: 0.01449
> Bloom filter space used: 1.34 MB
> Bloom filter off heap memory used: 1.33 MB
> At the same time I can see that the duration of GC has increased also> 
> There is a link between the increasment of the GC and the bloom
> filter ?> 
> Jean Carlo
> 

False positive increasing

[Jean Carlo]

Hello

Lately I am observing that the false positives of one of my nodes are
increasing in a continous way (1 per 5min)

Bloom filter false positives: 532
Bloom filter false ratio: 0.01449
Bloom filter space used: 1.34 MB
Bloom filter off heap memory used: 1.33 MB

At the same time I can see that the duration of GC has increased also

There is a link between the increasment of the GC and the bloom filter ?

Jean Carlo