Ah of course - question makes total sense.
But no: this is not the case: I am not constantly asking the same
question since the tree is deep enough. Most data nodes are level 5 from
the root. So the parents getting queried will be different most of the time.
Since the parent nodes are created the queries stop there and don't
propagate toward the root.
And I am seeing the high values all the time. Best that it gets is 0.15.
Daniel
On 27.10.10 18:37, Mike Malone wrote:
I think he was asking about queries, not data. The data may be
randomly distributed by way of a hash on the key, but if your queries
are heavily skewed (e.g., if you query for "foo" a lot more than
"foo/bar", and "foo" randomly happens to trigger a false positive) the
skew in your query pattern could cause a seemingly strange spike in
false positives.
With a hierarchical data model it's not unlikely that this sort of
skew exists since you'd tend to query for items towards the root of
the hierarchy more frequently.
Mike
On Wed, Oct 27, 2010 at 2:14 PM, Daniel Doubleday
<daniel.double...@gmx.net <mailto:daniel.double...@gmx.net>> wrote:
Hm -
not sure if I understand the random question. We are using RP. But
I wouldn't know why that should matter.
I thought that the bloom filter hash function should evenly
distribute no matter what keys come in.
Keys are '/' separated strings (aka paths :-))
I do bulk inserts like: (1000 rows at a time, with ~ 50 cols each)
[
{'a/b/foo': cols},
{'a/b/bar': cols},
{'a/b/baz': cols}
]
and before that I would query for 'a/b'. Recursively as in mkdir -p
If parent paths are missing they would be inserted with the bulk
insert.
The value for BloomFilterFalseRatio has been in the range of 0.19
- 0.59 in the last couple of hours. Mostly around 0.3
We're on 0.6.6 btw
On Oct 27, 2010, at 3:58 PM, Jonathan Ellis wrote:
> This is not expected, no. How random are your queries? If you
have a
> couple outlier rows causing the false positives that are being
queried
> over and over then that could just be the luck of the draw.
>
> On Wed, Oct 27, 2010 at 5:24 AM, Daniel Doubleday
> <daniel.double...@gmx.net <mailto:daniel.double...@gmx.net>> wrote:
>> Hi people
>>
>> We are currently moving our second use case from mysql to
cassandra. While importing the data (ongoing) I noticed that the
BloomFilterFalseRation seems to be pretty high compared to another
CF which is in used in production right now.
>>
>> Its a hierarchical data model and I cannot avoid to do a read
before inserting multiple columns.
>>
>> I see a false positive ration of 0.28 while in my other CF it
is 0.00025.
>>
>> The CF has 5 live sstables whiel I read that ratio. At that
time I inserted ~ 200k rows with a total of 1M cols. Row keys are
pretty large unfortunately (key.length() ~ 60)
>>
>> Just wanted to check if this value is to be expected.
>>
>>
>>
>> Thanks,
>> Daniel
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
