Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@cassandra.apache.org
Received-SPF: neutral (nike.apache.org: local policy)
Message-ID: <4E0641DA.6040207@dude.podzone.net>
Date: Sat, 25 Jun 2011 14:15:22 -0600
From: AJ <aj@dude.podzone.net>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US;
 rv:1.9.2.18) Gecko/20110616 Lightning/1.0b2 Thunderbird/3.1.11
MIME-Version: 1.0
To: user@cassandra.apache.org
Subject: Re: Concurrency: Does C* support a Happened-Before relation between
 processes' writes?
References: <4E04D867.4090900@dude.podzone.net>
	<BANLkTimnw0DONPv_yDOU7fmGg9bbdMMeQw@mail.gmail.com>
	<4E056512.30100@dude.podzone.net>
 <BANLkTinRxWsLVjWKEknhYnQLp+0TffhYHQ@mail.gmail.com>
In-Reply-To: <BANLkTinRxWsLVjWKEknhYnQLp+0TffhYHQ@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

On 6/25/2011 8:24 AM, Edward Capriolo wrote:
> I played around with the bakery algorithm and had ok success the
> challenges are most implementations assume an n size array of fixed
> clients and when you get it working it turns out to be a good number
> of cassandra ops to acquire your bakery lock.
>

I was thinking rather than making certain that there is a column 
reserved for each node and having to keep it updated, you can just over 
allocate a large number that would always be enough, like 100.  A slice 
of 100 byte-sized values shouldn't be a significant perf hit vs 3 or 4.  
If you only have 3 nodes in your cluster and the last 97 go unused, that 
would be ok; it would be as if those non-existent "customers" never take 
a number.

For optimizing for C*, I think you can get away with minimal getSlices 
for the loops.  If you're lucky, you can fall through all of them using 
the results from only 1 getSlice.  Only if a process is "entering" or 
has a higher priority number will you need to wait and then do another 
getSlice and only a slice for the remaining columns.  I think my logic 
is correct; do you agree?

Did you have other problems other than performance?