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Revathi Rangachari | 1 Mar 2012 19:16
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query_cache_type and Aborted Clients

Hi 

Can anyone please let me know: 
(1) if query_cache_type is disabled, will it result in the number of 'Aborted Clients' getting increased.  

The possible explanation I have is that because the slow queries are taking a long time to execute, and the
fact that the query_cache_type is also disabled, will it result in the clients getting disconnected from
the server due to wait_timeout set both at the mysql level and application level?  

In my mysql setup the wait_timeout is 30 secs and the query_cache_type is disabled. I have an ever
increasing number of Aborted Clients 

+------------------+--------+
| Variable_name    | Value  |
+------------------+--------+
| Aborted_clients  | 661117 |
| Aborted_connects | 156    |
+------------------+--------+

The wait_timeout at application level is 5 secs.

Thanks in advance for any explanation on my query
Revathi R

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Rick James | 1 Mar 2012 22:23
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Re: query_cache_type and Aborted Clients

Which wait_timeout?  There are about 3 -- session vs global and 
interactive versus batch.

query_cache is (probably) totally independent of connections.

Aborted_clients is since startup, and will be "ever increasing" -- 
useless without dividing by something:

Aborted_clients/Uptime -- if > 1, then increase wait_timeout
Aborted_clients/Connections -- if > 30, then increase wait_timeout
Aborted_connects/Uptime -- when this is > 1, you might have a hacker 
trying to get in
Connections/Uptime -- if > 1, you might think about why you need to 
reconnect so often.

If a client sits there too long (more than wait_timeout), he will be 
disconnected.  30 seconds is plenty for web-type applications.

For investigating slow queries, please provide
* SHOW CREATE TABLE
* SHOW TABLE STATUS
* EXPLAIN SELECT ...
* SHOW VARIABLES LIKE '%buffer%'; and how much RAM do you have?

On 3/1/12 10:16 AM, Revathi Rangachari wrote:
> Hi
>
> Can anyone please let me know:
> (1) if query_cache_type is disabled, will it result in the number of 'Aborted Clients' getting increased.
>
(Continue reading)

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nyaghma | 2 Mar 2012 00:03
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Question about developing mysql cluster

Hi,

I am Navid Yaghmazaeh, a Ph.D. student at the University of Texas at  
Austin. I'm member of a team working on a research project about  
adding some features to mysql cluster. A brief description of our  
project is that we are working on making mysql more durable by storing  
logs on disk at the end of each transaction. We want
to add this property to mysql in parallel to current property of  
making state of the system durable by epochs, so mysql cluster could  
support both level of durability at the same time.

In order to do so, we have to modify the Ndb code. I have some  
question about changing the mysql cluster code and if you could help  
me I would be greatly thankful.

Could you please link me to documents about protocols used in Ndb,  
specially in Ndb kernel, such as global checkpointing protocol or two  
phase commit protocol and protocols for committing transactions.? I  
have read the "Mysql Cluster API Developer Guide", but it is mostly  
about the Ndb API, and does not describe the Ndb kernel and the  
protocols used there.

Could please guide me where could be a good point to start modifying  
Ndb kernel code? As Ndb is a huge code and has many different modules  
which work together though they are separate in semantics, it would  
help a lot if you could help me about choosing a good starting point  
for applying changes.

Is there any available unit and integrity tests available in order to  
be able to test our changes and make sure everything is going well?
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Revathi Rangachari | 5 Mar 2012 19:36
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Re: query_cache_type and Aborted Clients

Hi Rick 

Thanks for the explanation.  

(1)  wait_timeout is global..in my setup.

(2) > Aborted_connects/Uptime -- when this is > 1, you might
> have a hacker > trying to get in - 
...........In my case this is 2. How will I find out a hacker is trying to get in? My log_warnings is set to 1.

(3)  Disabling query_cache_type  - will it increase the CPU utilization? 

(4)  For investigating slow queries, I will not be in a position to share all the information that you had
asked for, due to security policies, however if you can provide some guideline as to how to proceed with the
investigations using the commands given below, I will give it a try.  

Thanks
Revathi R

--- On Fri, 3/2/12, Rick James <rjames <at> yahoo-inc.com> wrote:

> From: Rick James <rjames <at> yahoo-inc.com>
> Subject: Re: query_cache_type and Aborted Clients
> To: internals <at> lists.mysql.com
> Date: Friday, March 2, 2012, 2:53 AM
> Which wait_timeout?  There are
> about 3 -- session vs global and 
> interactive versus batch.
> 
> query_cache is (probably) totally independent of
(Continue reading)

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Rick James | 5 Mar 2012 19:55
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Re: query_cache_type and Aborted Clients

I don't know how to spot a hacker.  The available protection:
* Limit SUPER to root <at> localhost
* All applications are GRANT ... ON dbname.* ... -- so that if a hacker 
does get in (or there is "sql injection", he cannot get to `mysql` db.
* read-write separation.  Where practical, have two different logins -- 
one for read+write parts of your app, one for readonly.  Again, the 
attempt is to limit the damage.
* Use sufficient hardened passwords (obviously) for _all_ logins.

Query cache --
If there is 'continual' write activity, the QC is useless -- _Any_ write 
to a table purges _all_ entries in the QC for that table.  That purging 
takes CPU effort, and blocks some operations.
Tables that never change, and have a lot of _identical_ queries, can 
benefit greatly from the QC.

Slow queries --
Obfuscate the names (but not the datatypes); we can help without 
compromising security.
There a zillion and one different cases.  I could write a book, and it 
would not be complete.

On 3/5/12 10:36 AM, Revathi Rangachari wrote:
> Hi Rick
>
> Thanks for the explanation.
>
> (1)  wait_timeout is global..in my setup.
>
> (2)>  Aborted_connects/Uptime -- when this is>  1, you might
(Continue reading)

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Revathi Rangachari | 7 Mar 2012 00:32
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have_query_cache and query_cache_type

Hi

(1)  Under what circumstances the have_query_cache can become 'NO'.

(2)  Is it possible to set it as 'YES'. When I tried to do that I get error message as - ERROR HY000: Variable
'have_query_cache' is a read only variable

(3) If have_query_cache is 'NO' and if I enable query_cache_type and set query_cache_size TO 128MB, will
the queries be read from the query cache?

Thanks
Revathi R

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Yves Trudeau | 7 Mar 2012 03:38
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Re: have_query_cache and query_cache_type

Hi,
   this is a compile option, the variable have_query_cache
is there to illustrate if the current binary has been compiled with the 
query cache or not.

Regards,

Yves

On 12-03-06 06:32 PM, Revathi Rangachari wrote:
> Hi
>
> (1)  Under what circumstances the have_query_cache can become 'NO'.
>
> (2)  Is it possible to set it as 'YES'. When I tried to do that I get error message as - ERROR HY000: Variable
'have_query_cache' is a read only variable
>
> (3) If have_query_cache is 'NO' and if I enable query_cache_type and set query_cache_size TO 128MB, will
the queries be read from the query cache?
>
> Thanks
> Revathi R
>
>
>

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Revathi Rangachari | 20 Mar 2012 21:21
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Slow query log file not getting updated

Hi

In one of the replicated slave servers, the slow query log file is not getting updated.  The configuration
settings in this slave are similar to other slaves.

Is there any other reason, why the slow query log file not getting updated? Updates were happening earlier. 
The log file was truncated once due to its increasing size. Could this be a reason for updates not happening?

Appreciate a line in reply

Thanks
Revathi R

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Baron Schwartz | 21 Mar 2012 12:32
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Re: Slow query log file not getting updated

The general MySQL list is better for this type of question.

The typical problem is that the server is writing to an open
filehandle that has been deleted from the filesystem, and the file
that you think the server should use is actually not open.  You can
find out like this on a typical Linux system:

$ lsof -p $(pidof mysqld) | grep deleted

On Tue, Mar 20, 2012 at 4:21 PM, Revathi Rangachari <masrrev <at> yahoo.com> wrote:
> Hi
>
> In one of the replicated slave servers, the slow query log file is not getting updated.  The
configuration settings in this slave are similar to other slaves.
>
> Is there any other reason, why the slow query log file not getting updated? Updates were happening
earlier.  The log file was truncated once due to its increasing size. Could this be a reason for updates
not happening?
>
> Appreciate a line in reply
>
> Thanks
> Revathi R
>
> --
> MySQL Internals Mailing List
> For list archives: http://lists.mysql.com/internals
> To unsubscribe:    http://lists.mysql.com/internals
>

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