I read that the change was made because Cassandra does not work well when they are off. This makes sense because cassandra uses bloom filters to decide if a row can be deleted without major compaction. However since LCS does not major compact without bloom filters you can end up in cases where rows never get deleted.


On Thu, Mar 7, 2013 at 4:30 PM, Wei Zhu <wz1975@yahoo.com> wrote:
Where did you read that bloom filters are off for LCS on 1.1.9?

Those are the two issues I can find regarding this matter:


Looks like in 1.2, it defaults at 0.1, not sure about 1.1.X


----- Original Message -----
From: "Michael Theroux" <mtheroux2@yahoo.com>
To: user@cassandra.apache.org
Sent: Thursday, March 7, 2013 1:18:38 PM
Subject: Bloom filters and LCS


(Hopefully) Quick question.

We are running Cassandra 1.1.9.

I recently converted some tables from Size tiered to Leveled Compaction.  The amount of space for Bloom Filters on these tables went down tremendously (which is expected, LCS in 1.1.9 does not use bloom filters).

However, although its far less, its still using a number of megabytes.  Why is it not zero?

                Column Family: XXXX
                SSTable count: 526
                Space used (live): 7251063348
                Space used (total): 7251063348
                Number of Keys (estimate): 23895552
                Memtable Columns Count: 45719
                Memtable Data Size: 21207173
                Memtable Switch Count: 579
                Read Count: 21773431
                Read Latency: 4.155 ms.
                Write Count: 16183367
                Write Latency: 0.029 ms.
                Pending Tasks: 0
                Bloom Filter False Positives: 2442
                Bloom Filter False Ratio: 0.00245
                Bloom Filter Space Used: 44674656
                Compacted row minimum size: 73
                Compacted row maximum size: 105778
                Compacted row mean size: 1104