cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Vladimir Yudovin <vla...@winguzone.com>
Subject Re: Will query on PK read entire partition?
Date Tue, 25 Apr 2017 18:27:29 GMT
Hi,



if you provide primary key C* will not scan whole partition, but will bloom filter to determinate
SSTable:

Cassandra uses Bloom filters to determine whether an SSTable has data for a particular row.
Bloom filters are unused for range scans, but are used for index scans.






Best regards, Vladimir Yudovin, 

Winguzone - Cloud Cassandra Hosting






---- On Fri, 21 Apr 2017 07:56:08 -0400 Alain RODRIGUEZ &lt;arodrime@gmail.com&gt;
wrote ----




Hi Oskar,



My guess (wait for confirmation maybe): When you read from a primary key + specific clustering
key or (range of clustering keys), Apache Cassandra will look for these specific values and
not read all the row. Yet it is important to know that a minimal block size of 64 KB is read
from the disk (not configurable in C* 2.0). Or if the table is compressed, the minimal read
size is a chunk, for which you can manually set the size. That's why when using small rows,
it is sometimes interesting to enable compression, even if you don't care about the data size...
This all has been improved a bit in 2.1 / 2.2 and greatly in C* 3.0+.



I might write a post about this, if I do, I will let you know. It's an interesting topic I
have been working on recently.



C*heers,

-----------------------

Alain Rodriguez - @arodream - alain@thelastpickle.com

France



The Last Pickle - Apache Cassandra Consulting

http://www.thelastpickle.com










2017-04-21 10:44 GMT+02:00 Oskar Kjellin &lt;oskar.kjellin@gmail.com&gt;:

If I have a table like this:



PRIMARY KEY ((userid),deviceid)



And I query

SELECT * FROM devices where userid= ? and deviceid = ?



Will cassandra read the entire partition for the userid? So if I lots of tombstones for userid,
will they get scanned?



I guess this depends on how the bloomfilter is working. Does it contain partitioning key or
primary key?



We're using 2.0.17 if it matters.



/Oskar










Mime
View raw message