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IDS Forum

Re: To read only committed rows from a table

Posted By: Bill Hamilton
Date: Wednesday, 4 January 2012, at 3:42 p.m.

In Response To: Re: To read only committed rows from a table (Fernando Nunes)

1. I am trying that out
2. I don't do Java
3. I looked for that but could not find
4. I guess you mean "USELASTCOMMITTED ALL" or "USELASTCOMMITTED COMMITTED
READ" in onconfig file . I use ALL (tough guy). What sort of breakage would
I look for?

5. I would vote for it but now that John Miller has educated me on
public.sysdbopen() I suppose I don't need it.
6. I wonder if there would be any overhead difference the other way
(onconfig variable) .
7. What breakage would you see for WAIT 10 as opposed to NOT WAIT ? It
should not slow down since the wait occurs only when a lock is hit. Maybe a
program could be looking for a stuck lock to do some other work? Hard to
imagine unless it is the dba.

-----Original Message-----
From: Fernando Nunes
Sent: Wednesday, January 04, 2012 1:04 PM
To: ids@iiug.org
Subject: Re: To read only committed rows from a table [25816]

I feel your pain... And there will always be unhappy people because some
features were not implemented yet... But there are a few improvements that
can help:

1- You can set it in sysdbopen()
2- You can set it in Java URls
3- I beleive you can set it in ODBC connection strings (I should have
checked this)
4- You could automatically move all COMMITTED READ to COMMITTED READ LAST
COMMITTED (do you dare to do it?..)

But yes... I would vote for that... Although I'm not sure if many customers
would use it... It could break things...
Regards.

On Wed, Jan 4, 2012 at 6:21 PM, Bill Hamilton <garage_dba@hotmail.com>wrote:

> Speaking of lock mode --- is there STILL no way to set it in onconfig file
> to default to "wait X" or do we still have to set after each connection ?
> ( I am speaking of 11.70.TC3IE)
> It is wasteful to execute the "set" statement (in c++ or c# or whatever)
> upon each connection.
> If "not wait" is set then one must loop to retry an update ( also
> wasteful ). If you don't, then things rollback on a busy server and users
> get unhappy.
> With all the improvements done to IDS one would think that the lock mode
> default would be put into onconfig.
> Was IBM just to busy to fix this, or do they like us to suffer or make our
> own code harder to read?
> I did have several programs (written by departed programmers) that blew
> out
> at busy times.
> When I added "set lock mode to wait 10" the problems went away completely.
> Ten seconds is like infinity and the next waiter gets the row.
> ( all tables use row locking)
>
> -----Original Message-----
> From: Fernando Nunes
> Sent: Wednesday, January 04, 2012 4:28 AM
> To: ids@iiug.org
> Subject: Re: To read only committed rows from a table [25807]
>
> Ths committed read is working as expected. It tells the engine that it
> should not ignore other session locks (like dirty read does) and at the
> same time that it should not lock the rows it reads (like repeatable read
> does). The session behavior when working in committed read, when it finds
> a
> lock depends on the LOCK MODE.
> If LOCK MODE is set to NOT WAIT the session immediately receives an error.
> If it's WAIT n, then it waits at most "n" seconds. If after "n" seconds
> the
> lock is still there, the error is raised. Finally it you SET LOCK MODE TO
> WAIT; (without a number) then the session will wait forever.
>
> This is how it works, and it's explained in the manual.
> In your specific case I think you need to check why the other process is
> holding locks for 2 minutes and try to reduce that time.
> The condition on the timestamp could be used if you set it to
> "timestamp_field < CURRENT - 2 UNITS MINUTE" for example... but for this
> to
> work you'd probably need an index on that column... If you're doing a full
> scan for example, you'd hit the locks anyway...
>
> Or you could "accept" the error and process whatever lines you get... And
> retry later hoping that you'll grab some more rows and so on... This could
> be a way to do it assuming both processes are run frequently and
> concurrently. If not, than simply offset the execution times of both
> processes.
>
> To end this, this is a clear example of the costs of being stuck with old
> versions...
> Regards.
>
> On Wed, Jan 4, 2012 at 9:37 AM, NAVEEN NAIK <navnaik@gmail.com> wrote:
>
> > Thanks all for your replays.
> >
> > I should have mentioned the Informix version I am using. Apologies for
> > that.
> >
> > I am using the IDS 9.4
> >
> > The last committed is not working here :-(
> >
> > Is there any other way around this.
> >
> > I am also retrieving based on time stamp, but I am using a multi user
> > environment.
> > Some rows are committed before others.
> >
> > Row1 <Data> | 04-01-2012 10:33:33 | - Not yet committed
> > Row2 <Data> | 04-01-2012 10:33:34 | - Committed
> >
> > Sometimes, Row2 with a greater time stamp gets committed before the
> > another
> > row which has lesser time stamp. And since row 1 is not committed I am
> > getting
> > the error.
> >
> > I was under the assumption that SET ISOLATION TO COMMITTED READ should
> > have
> > worked. Still wondering why it is not working.
> >
> > Regards,
> > Naveen Naik
> >
> >
> >
> >
>
>
>
*******************************************************************************
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
> >
>
> --
> Fernando Nunes
> Portugal
>
> http://informix-technology.blogspot.com
> My email works... but I don't check it frequently...
>
> --20cf3063e337f5f83804b5b145ff
>
>
>
>
*******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>
>
>
*******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--
Fernando Nunes
Portugal

http://informix-technology.blogspot.com
My email works... but I don't check it frequently...

--20cf300fae91c8356904b5b87bc5

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