At the DataStax Cassandra Summit 2013 last week, Al Tobey from Ooyala recommended ss_table_size_in_mb be set at 256mb unless you have a fairly small data set.  The talk was "Extreme Cassandra Optimization," and it was superbly informative, I highly recommend it once DataStax gets the videos online.


On Mon, Jun 17, 2013 at 1:35 AM, Wei Zhu <wz1975@yahoo.com> wrote:
Correction, the largest I heard is 256MB SSTable size.


From: "Wei Zhu" <wz1975@yahoo.com>
To: user@cassandra.apache.org
Sent: Sunday, June 16, 2013 10:28:25 PM

Subject: Re: Large number of files for Leveled Compaction

default value of 5MB is way too small in practice. Too many files in one directory is not a good thing. It's not clear what should be a good number. I have heard people are using 50MB, 75MB, even 100MB. Do your own test o find a "right" number.

-Wei


From: "Franc Carter" <franc.carter@sirca.org.au>
To: user@cassandra.apache.org
Sent: Sunday, June 16, 2013 10:15:22 PM
Subject: Re: Large number of files for Leveled Compaction



On Mon, Jun 17, 2013 at 2:59 PM, Manoj Mainali <mainalimanoj@gmail.com> wrote:
Not in the case of LeveledCompaction. Only SizeTieredCompaction merges smaller sstables into large ones. With the LeveledCompaction, the sstables are always of fixed size but they are grouped into different levels.

You can refer to this page http://www.datastax.com/dev/blog/leveled-compaction-in-apache-cassandra on details of how LeveledCompaction works.


Yes, but it seems I've misinterpreted that page ;-(

I took this paragraph

In figure 3, new sstables are added to the first level, L0, and immediately compacted with the sstables in L1 (blue). When L1 fills up, extra sstables are promoted to L2 (violet). Subsequent sstables generated in L1 will be compacted with the sstables in L2 with which they overlap. As more data is added, leveled compaction results in a situation like the one shown in figure 4.

to mean that once a level fills up it gets compacted into a higher level

cheers
 
Cheers
Manoj


On Mon, Jun 17, 2013 at 1:54 PM, Franc Carter <franc.carter@sirca.org.au> wrote:
On Mon, Jun 17, 2013 at 2:47 PM, Manoj Mainali <mainalimanoj@gmail.com> wrote:
With LeveledCompaction, each sstable size is fixed and is defined by sstable_size_in_mb in the compaction configuration of CF definition and default value is 5MB. In you case, you may have not defined your own value, that is why your each sstable is 5MB. And if you dataset is huge, you will see a lot of sstable counts.


Ok, seems like I do have (at least) an incomplete understanding. I realise that the minimum size is 5MB, but I thought compaction would merge these into a smaller number of larger sstables ?

thanks


Cheers

Manoj


On Fri, Jun 7, 2013 at 1:44 PM, Franc Carter <franc.carter@sirca.org.au> wrote:

Hi,

We are trialling Cassandra-1.2(.4) with Leveled compaction as it looks like it may be a win for us.

The first step of testing was to push a fairly large slab of data into the Column Family - we did this much faster (> x100) than we would in a production environment. This has left the Column Family with about 140,000 files in the Column Family directory which seems way too high. On two of the nodes the CompactionStats show 2 outstanding tasks and on a third node there are over 13,000 outstanding tasks. However from looking at the log activity it looks like compaction has finished on all nodes.

Is this number of files expected/normal ?

cheers

--

Franc Carter | Systems architect | Sirca Ltd

franc.carter@sirca.org.au | www.sirca.org.au

Tel: +61 2 8355 2514

Level 4, 55 Harrington St, The Rocks NSW 2000

PO Box H58, Australia Square, Sydney NSW 1215






--

Franc Carter | Systems architect | Sirca Ltd

franc.carter@sirca.org.au | www.sirca.org.au

Tel: +61 2 8355 2514

Level 4, 55 Harrington St, The Rocks NSW 2000

PO Box H58, Australia Square, Sydney NSW 1215






--

Franc Carter | Systems architect | Sirca Ltd

franc.carter@sirca.org.au | www.sirca.org.au

Tel: +61 2 8355 2514

Level 4, 55 Harrington St, The Rocks NSW 2000

PO Box H58, Australia Square, Sydney NSW 1215