"remember is used more IO than STS" Are you meaning during compactions ? Because I thought that LCS should decrease the number of disks reads (since 90% of the data aren't spread across multiple sstables and C* needs to read only a file to find the entire row) while not compacting right ?
2013/3/28 aaron morton <aa...@thelastpickle.com> > 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 ) > > So that's not good. > If IO is saturated then maybe LCS is not for you, remember is used more IO > than STS. > Otherwise look at the compaction yaml settings to see if you can make it > go faster but watch out that you don't hurt normal requests. > > CHeers > > ----------------- > Aaron Morton > Freelance Cassandra Consultant > New Zealand > > @aaronmorton > http://www.thelastpickle.com > > On 28/03/2013, at 7:00 AM, Wei Zhu <wz1...@yahoo.com> wrote: > > Welcome to the wonderland of SSTableSize of LCS. There is some discussion > around it, but no guidelines yet. > > I asked the people in the IRC, someone is running as high as 128M on the > production with no problem. I guess you have to test it on your system and > see how it performs. > > Attached is the related thread for your reference. > > -Wei > > ----- Original Message ----- > From: "Andras Szerdahelyi" <andras.szerdahe...@ignitionone.com> > To: user@cassandra.apache.org > Sent: Wednesday, March 27, 2013 1:19:06 AM > Subject: Re: bloom filter fp ratio of 0.98 with fp_chance of 0.01 > > > 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 > > Reply-To: " user@cassandra.apache.org " < user@cassandra.apache.org > > Date: Tuesday 26 March 2013 21:46 > To: " user@cassandra.apache.org " < 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 > 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 > <attachment.eml> > > >
