Re: [Postgres-xc-general] ERROR: Failed to get pooled connections

[Vladimir S. <vst...@gm...>]

On Wed, Oct 24, 2012 at 08:08:32PM +0900, Michael Paquier wrote:

>    Sure, XC provides thanks to its architecture naturally transparency and scalability.

What does XC provides? My two rhetorical questions above imply answers
"NO".  Necessity to adapt application means cluster is not transparent.
Impossibility to extend cluster online means it is not scalable.

More over, this two issues are interrelated, because You should rewrite
"CREATE TABLE" statement every time you expand (read: recreate) Your
cluster. But this issue looks much worse if node fails containing tables
with different distributed schemas. This is uncontrollable model.

>    Load balancing can be provided between Coordinator and Datanodes
>    depending on applications, or at Coordinator level

It should not depend on application, it should be an cluster's global function.

>    For HA, Koichi is currently working on some tools to provide that,

Again: it should not be external tool, it should be internal, integral,
essential feature.

>    I am not sure you can that easily compare XC and mysql cluster,
>    both share the same architectures, but once of the main

I don't know what there is "the same", but in functionality it is
totally different. Mysql cluster has the precise and clear clustering
model:

1. If some nodes fail cluster continues to work as soon as there remains
at least one healthy node in every group.

2. No "CREATE TABLE ... DISTRIBUTE BY ..." statement. You just define
the number of replicas at configuration level. Yes, now there are only
one option is available that make sense with two replicas, but it is
enough.

3. Read and write scalability (i.e. LB) at the same time for all tables
(i.e. on the cluster level).

4. You can add data node online, i.e. without restarting (not to mention
"recreating" as for XC) cluster. Yes, only new data will go to the new
node in this case. But You can totally redistribute it with restart.

So it is full flagged cluster, that's not true for XC and it's a pity.

>    differences coming to my mind is that XC is far more flexible in
>    terms of license (BSD and not GPL), and like PostgreSQL, no company
>    has the control of its code like mysql products which Oracle relies

Yes, and this is why I am persuading all developers migrate to
Postgresql. But it is off topic here where we are discussing
functionality, but not an licence issues. 

Be tolerant to my criticism, I wouldn't say You made bad thing, I was
amazing when first read "write-scalable, synchronous multi-master,
transparent PostgreSQL cluster" in Your description that I completely
and exactly copied into description of my debian package, but I was
notably disappointed after my first test showing me that it is odd with
reality. It would not be so bad itself, as soon as it is young project,
but much worse that this discussion shows there are something wrong with
Your priorities and fundamental approach.

-- 

***************************
##  Vladimir Stavrinov
##  vst...@gm...
***************************