Aaron, What version are you using ?
1.1.9 Have you changed the bf_ chance ? The sstables need to be rebuilt for it to take affect. I did ( several times ) and I ran upgradesstables after Not sure what this means. Are you saying it's in a boat on a river, with tangerine trees and marmalade skies ? You nailed it. A significant number of reads are done from hundreds of sstables ( I have to add, compaction is apparently constantly 6000-7000 tasks behind and the vast majority of the reads access recently written data ) Take a look at the nodetool cfhistograms to get a better idea of the row size and use that info when consdiering the sstable size. It's around 1-20K, what should I optimise the LCS sstable size for? I suppose "I want to fit as many complete rows as possible in to a single sstable to keep file count down while avoiding compactions of oversized ( double digit gigabytes? ) sstables at higher levels ? " Do I have to run a major compaction after a change to sstable_size_in_mb ? The larger sstable size wouldn't really affect sstables on levels above L0 , would it? Thanks!! Andras From: aaron morton <aa...@thelastpickle.com<mailto:aa...@thelastpickle.com>> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Date: Tuesday 26 March 2013 21:46 To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Subject: Re: bloom filter fp ratio of 0.98 with fp_chance of 0.01 What version are you using ? 1.2.0 allowed a null bf chance, and I think it returned .1 for LCS and .01 for STS compaction. Have you changed the bf_ chance ? The sstables need to be rebuilt for it to take affect. and sstables read is in the skies Not sure what this means. Are you saying it's in a boat on a river, with tangerine trees and marmalade skies ? SSTable count: 22682 Lots of files there, I imagine this would dilute the effectiveness of the key cache. It's caching (sstable, key) tuples. You may want to look at increasing the sstable_size with LCS. Compacted row minimum size: 104 Compacted row maximum size: 263210 Compacted row mean size: 3041 Take a look at the nodetool cfhistograms to get a better idea of the row size and use that info when consdiering the sstable size. Cheers ----------------- Aaron Morton Freelance Cassandra Consultant New Zealand @aaronmorton http://www.thelastpickle.com On 26/03/2013, at 6:16 AM, Andras Szerdahelyi <andras.szerdahe...@ignitionone.com<mailto:andras.szerdahe...@ignitionone.com>> wrote: Hello list, Could anyone shed some light on how an FP chance of 0.01 coexist with a measured FP ratio of .. 0.98 ? Am I reading this wrong or are 98% of the requests hitting the bloom filter create a false positive while the "target" false ratio is 0.01? ( Also key cache hit ratio is around 0.001 and sstables read is in the skies ( non-exponential (non-) drop off for LCS ) but that should be filed under "effect" and not "cause"? ) [default@unknown] use KS; Authenticated to keyspace: KS [default@KS] describe CF; ColumnFamily: CF Key Validation Class: org.apache.cassandra.db.marshal.BytesType Default column value validator: org.apache.cassandra.db.marshal.BytesType Columns sorted by: org.apache.cassandra.db.marshal.BytesType GC grace seconds: 691200 Compaction min/max thresholds: 4/32 Read repair chance: 0.1 DC Local Read repair chance: 0.0 Replicate on write: true Caching: ALL Bloom Filter FP chance: 0.01 Built indexes: [] Compaction Strategy: org.apache.cassandra.db.compaction.LeveledCompactionStrategy Compaction Strategy Options: sstable_size_in_mb: 5 Compression Options: sstable_compression: org.apache.cassandra.io.compress.SnappyCompressor Keyspace: KS Read Count: 628950 Read Latency: 93.19921121869784 ms. Write Count: 1219021 Write Latency: 0.14352380885973254 ms. Pending Tasks: 0 Column Family: CF SSTable count: 22682 Space used (live): 119771434915 Space used (total): 119771434915 Number of Keys (estimate): 203837952 Memtable Columns Count: 13125 Memtable Data Size: 33212827 Memtable Switch Count: 15 Read Count: 629009 Read Latency: 88.434 ms. Write Count: 1219038 Write Latency: 0.095 ms. Pending Tasks: 0 Bloom Filter False Positives: 37939419 Bloom Filter False Ratio: 0.97928 Bloom Filter Space Used: 261572784 Compacted row minimum size: 104 Compacted row maximum size: 263210 Compacted row mean size: 3041 I upgraded sstables after changing the FP chance Thanks! Andras
