Hi Nikolai, Thanks for those informations.
Please could you clarify a little bit what you call " 2014-11-24 4:37 GMT+01:00 Nikolai Grigoriev <ngrigor...@gmail.com>: > Just to clarify - when I was talking about the large amount of data I > really meant large amount of data per node in a single CF (table). LCS does > not seem to like it when it gets thousands of sstables (makes 4-5 levels). > > When bootstraping a new node you'd better enable that option from > CASSANDRA-6621 (the one that disables STCS in L0). But it will still be a > mess - I have a node that I have bootstrapped ~2 weeks ago. Initially it > had 7,5K pending compactions, now it has almost stabilized ad 4,6K. Does > not go down. Number of sstables at L0 is over 11K and it is slowly slowly > building upper levels. Total number of sstables is 4x the normal amount. > Now I am not entirely sure if this node will ever get back to normal life. > And believe me - this is not because of I/O, I have SSDs everywhere and 16 > physical cores. This machine is barely using 1-3 cores at most of the time. > The problem is that allowing STCS fallback is not a good option either - it > will quickly result in a few 200Gb+ sstables in my configuration and then > these sstables will never be compacted. Plus, it will require close to 2x > disk space on EVERY disk in my JBOD configuration...this will kill the node > sooner or later. This is all because all sstables after bootstrap end at L0 > and then the process slowly slowly moves them to other levels. If you have > write traffic to that CF then the number of sstables and L0 will grow > quickly - like it happens in my case now. > > Once something like https://issues.apache.org/jira/browse/CASSANDRA-8301 > is implemented it may be better. > > > On Sun, Nov 23, 2014 at 4:53 AM, Andrei Ivanov <aiva...@iponweb.net> > wrote: > >> Stephane, >> >> We are having a somewhat similar C* load profile. Hence some comments >> in addition Nikolai's answer. >> 1. Fallback to STCS - you can disable it actually >> 2. Based on our experience, if you have a lot of data per node, LCS >> may work just fine. That is, till the moment you decide to join >> another node - chances are that the newly added node will not be able >> to compact what it gets from old nodes. In your case, if you switch >> strategy the same thing may happen. This is all due to limitations >> mentioned by Nikolai. >> >> Andrei, >> >> >> On Sun, Nov 23, 2014 at 8:51 AM, Servando Muñoz G. <smg...@gmail.com> >> wrote: >> > ABUSE >> > >> > >> > >> > YA NO QUIERO MAS MAILS SOY DE MEXICO >> > >> > >> > >> > De: Nikolai Grigoriev [mailto:ngrigor...@gmail.com] >> > Enviado el: sábado, 22 de noviembre de 2014 07:13 p. m. >> > Para: user@cassandra.apache.org >> > Asunto: Re: Compaction Strategy guidance >> > Importancia: Alta >> > >> > >> > >> > Stephane, >> > >> > As everything good, LCS comes at certain price. >> > >> > LCS will put most load on you I/O system (if you use spindles - you may >> need >> > to be careful about that) and on CPU. Also LCS (by default) may fall >> back to >> > STCS if it is falling behind (which is very possible with heavy writing >> > activity) and this will result in higher disk space usage. Also LCS has >> > certain limitation I have discovered lately. Sometimes LCS may not be >> able >> > to use all your node's resources (algorithm limitations) and this >> reduces >> > the overall compaction throughput. This may happen if you have a large >> > column family with lots of data per node. STCS won't have this >> limitation. >> > >> > >> > >> > By the way, the primary goal of LCS is to reduce the number of sstables >> C* >> > has to look at to find your data. With LCS properly functioning this >> number >> > will be most likely between something like 1 and 3 for most of the >> reads. >> > But if you do few reads and not concerned about the latency today, most >> > likely LCS may only save you some disk space. >> > >> > >> > >> > On Sat, Nov 22, 2014 at 6:25 PM, Stephane Legay <sle...@looplogic.com> >> > wrote: >> > >> > Hi there, >> > >> > >> > >> > use case: >> > >> > >> > >> > - Heavy write app, few reads. >> > >> > - Lots of updates of rows / columns. >> > >> > - Current performance is fine, for both writes and reads.. >> > >> > - Currently using SizedCompactionStrategy >> > >> > >> > >> > We're trying to limit the amount of storage used during compaction. >> Should >> > we switch to LeveledCompactionStrategy? >> > >> > >> > >> > Thanks >> > >> > >> > >> > >> > -- >> > >> > Nikolai Grigoriev >> > (514) 772-5178 >> > > > > -- > Nikolai Grigoriev > (514) 772-5178 >
