Re: Cluster performance with data node down

Stewart Smith wrote:
> On Wed, 2007-08-15 at 20:02 +0200, Giulio Ferro wrote:
>
>> What we are talking about here is a query which on a single machine
>> configuration (no cluster) takes less than .3 sec. to complete.
>>
>> So we have
>> Time to complete select query :
>> *) single machine - no cluster : < 0.3 seconds
>> *) cluster - 2/2 data nodes : < 0.4 seconds
>> *) cluster - 1/2 data nodes : > 12 seconds.
>>
>> What we have here is a configuration without any workload (except
>> the query I execute). As far as I can tell there is no task here which
>> can benefit from parallelization.
>>
>> But even if it were, parallelization could in no way account for a
>> difference in execution of a factor of 30 (12 / 0.4)
>>
>> As a software architect my guess is that here we have something
>> of an anomaly in the way things are managed in a degraded cluster.
>>
>> I could also add data nodes, but unless some of you explains to me
>> how this could really set things right I'm still thinking we are barking
>> at the wrong tree...
>>
>
> What queries? on what tables? on what data set? EXPLAIN output?
>
> cluster configuration?
>
>

Again, from original message:

Here's the setup:
2 sql node + 2 data node interconnected by a gigabit switch used just by the cluster.
Mysql version : 5.1.20
Freebsd 6.2 stable amd64 (source update : 2 days ago) DataMemory : 6500M
IndexMemory : 500M
Tables are created in a tablespace

Under normal circumstances and after the first query, the performance is acceptable : standard select queries in my test db take about .3 / .4 sec
to complete.

The problems start when I take a data node down (gracefully, with the command "<nodeid> stop"). When I do that the time to complete the same queries rises to an unacceptable 12 seconds and stays that way.

Then I start the node again and performances go back to what they were before.

The query is a simple select on a single table. The tables contains about 330.000 entries. The queries executed are like this: select * from <tablename> where <varchar_field> = '....'; select * from <tablename> where <varchar_field> like '%....%';

<varchar_field> is a varchar(255) and is also an index.

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explain output:

+----+-------------+----------------+------+---------------+------+---------+------+--------+-----------------------------------+
| id | select_type | table          | type | possible_keys | key  | 
key_len | ref  | rows   | Extra                             |
+----+-------------+----------------+------+---------------+------+---------+------+--------+-----------------------------------+
|  1 | SIMPLE      |  | ALL  | NULL          | NULL | NULL    

+----+-------------+----------------+------+---------------+------+---------+------+--------+-----------------------------------+

I hope it helps.

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