Re: Review: DTrace probes (merged version) ver_03

Tom Lane wrote:
>
> * The probes that pass buffer tag elements are already broken by the
> pending "relation forks" patch: there is soon going to be another field
> in buffer tags.  Perhaps it'd be feasible to pass the buffer tag as a 
> single probe argument to make that a bit more future-proof?  I'm not
> sure if that would complicate the use of the probe so much as to be
> counterproductive.
>   
Are you referring to this struct?

typedef struct buftag
{       RelFileNode rnode;                      /* physical relation 
identifier */       BlockNumber blockNum;           /* blknum relative to begin of 
reln */
} BufferTag;

I'm not familiar with this pending patch, but why would it break when 
another field is added?

It's certainly possible to pass the buffer tag, but I'd say it's not a 
good idea if the other fields will never be used.

> * I find this to be truly bletcherous:
>
>   
>> !     /* 
>> !      * Due to a bug in Mac OS X 10.5, using defined types (e.g. uintptr_t,
>> !      * uint32_t, etc.) cause compilation error.  
>> !      */
>> !       
>> !     probe transaction__start(unsigned int transactionId);
>> !     probe transaction__commit(unsigned int transactionId);
>> !     probe transaction__abort(unsigned int transactionId);
>>     
>
> especially since some of the manual translations in the file are flat
> out wrong (Oid is unsigned for instance).
Oops!
>   Furthermore the comment is
> wrong, at least according to my tests with XCode 3.1.  Typedefs seem to
> work fine.

The issue is with Apple's dtrace implementation, not Xcode. For more 
info, please see the link below.

http://www.opensolaris.org/jive/thread.jspa?messageID=252503&#252503


> What I suggest might be a reasonable compromise is to copy needed
> typedefs directly into the probes.d file:
>
>     typedef unsigned int LocalTransactionId;
>
>     provider postgresql {
>
>     probe transaction__start(LocalTransactionId);
>
>   
I like this solution.

-- 
Robert Lor           Sun Microsystems
Austin, USA          http://sun.com/postgresql