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From Katherine Marsden <kmarsdende...@sbcglobal.net>
Subject Re: when should a user run SYSCS_INVALIDATE_STORED_STATEMENTS?
Date Wed, 24 Oct 2012 18:29:32 GMT
On 10/24/2012 11:06 AM, Rick Hillegas wrote:
> I'm wondering what we should tell users about the new 
> SYSCS_INVALIDATE_STORED_STATEMENTS procedure. Should we say:
I'd vote for 1 with a bit more of an explanation:

I) Run SYSCS_INVALIDATE_STORED_STATEMENTS whenever you think that your 
metadata queries or triggers are mis-behaving, for example if they  
throw a NoSuchMethod error on execution. Derby stores plans for triggers 
and metadata queries in the database.  These should be invalidated 
automatically on upgrade and at other necessary times.  Should you 
encounter an instance where they are not,  you have found a bug that you 
should report, but one that you can likely  work around by running 
SYSCS_INVALIDATE_STORED_STATEMENTS.


>
> I) Run SYSCS_INVALIDATE_STORED_STATEMENTS whenever you think that your 
> metadata queries or triggers are mis-behaving.
>
> II) Run SYSCS_INVALIDATE_STORED_STATEMENTS whenever you upgrade the 
> version of Derby which you are using.
>
> III) Only run SYSCS_INVALIDATE_STORED_STATEMENTS when tech supports 
> tells you to.
>
> IV) Something else?
>
> What follows are some additional musings which led me to ask this 
> question.
>
> Thanks,
> -Rick
>
> ---------------------------------------------------
>
>
> My first step in buddy-testing the SYSCS_INVALIDATE_STORED_STATEMENTS 
> procedure was to read the user documentation in the Reference Manual. 
> The section on SYSCS_INVALIDATE_STORED_STATEMENTS talks about stored 
> prepared statements and mentions the SYSSTATEMENTS table.
>
> I don't think that our doc set explains, anywhere, what a stored 
> prepared statement is. The Reference Manual section on SYSSTATEMENTS 
> doesn't explain what they are or why Derby creates them. I imagine 
> users must be a little confused by the explanation for 
> SYSTATEMENTS.USINGTEXT, which refers to the otherwise undocumented 
> CREATE STATEMENT and ALTER STATEMENT syntax. And I can't find any 
> other explanation of stored prepared statements in our doc set.
>
> So when I read the section on SYSCS_INVALIDATE_STORED_STATEMENTS, I 
> imagined that a user might ask:
>
> 1) How do I know that I need to run this procedure?
>
> 2) Should I run this procedure every time I hard-upgrade the database?
>
> 3) Should I run this procedure whenever I upgrade the version of Derby 
> which I'm using?
>
> I think that the following is true:
>
> a) Derby persists stored prepared statements in order to improve the 
> performance of metadata queries and triggers the first time they run 
> after the database has booted. That is, stored prepared statements are 
> meant to save the first user the cost of compiling a metadata query or 
> trigger.
>
> b) There are only 2 reasons for a user to forcibly recompile a stored 
> prepared statement:
>
>   i) Derby had a bug when it originally compiled the metadata query or 
> trigger and now that bug has been fixed.
>
>   ii) The persistent form of query plans has changed between versions 
> of Derby and the old metadata and trigger plans need to be discarded.
>
>


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