Proposed changes to DTrace probe implementation

[Robert Lor <Robert(dot)Lor(at)Sun(dot)COM>]

Motivation:
To enable probes to work with Mac OS X Leopard and other OSes that will 
support DTrace in the future. Bug filed on this issue 
http://archives.postgresql.org/pgsql-bugs/2007-10/msg00201.php

The problem:
There are two different mechanisms to implementing application level 
probes in DTrace as explained here 
http://blogs.sun.com/ahl/entry/user_land_tracing_gets_better. I 
originally chose the first mechanism (using DTRACE_PROBEn macros) for 
simplicity, but Leopard's DTrace implementation only supports the second 
mechanism (using macros from dtrace generated header file). The second 
mechanism was introduced as an enhancement, and one of the benefits is 
type checking.

Proposed changes:
* Switch from using DTRACE_PROBEn macros to the dynamically generated 
macros (remove pg_trace.h)
* Use "dtrace -h" to create a header file that contains the dynamically 
generated macros to be used in the source code instead of the 
DTRACE_PROBEn macros.
* Create a new header file called probes_null.h to map the generated 
macros to no-ops
* This is unrelated to making DTrace work on Leopard, but I'd like to 
propose that we split the probes into generic database and Postgres 
specific providers, called "database" and "postgresql" respectively. 
Other databases will be adding DTrace probes as well, and we want to use 
"database" as the provider for probes that are common to all databases. 
This way scripts that use the common provider will work on databases 
that implement the common probes.

With the proposed changes, the steps for adding new probes are slightly 
different, but the ways the probes are used will not change.

Steps for adding new probes now:
1) Add probe name to probes.d
2) Add probe to source code using one of PG_TRACEn macros
3) Recompile

Steps for adding probes with proposed changes:
1) Add probe name to probes.d (probes.h will be created at build time)
2) Add null macros to probes_null.h
3) Add probe to source code using the dynamically generated macro from 
probes.h
4) Recompile

Preliminary patch is attached. There is one known issue with the patch. 
When compiling outside of the source tree, probes.d needs to be 
symlinked to the source tree. I haven't figured out how to copy the file 
to the build tree yet.  I'm sure this is trivial for you gurus out there!

Comments?

Regards,
-Robert

? src/include/probes_null.h
Index: src/Makefile
===================================================================
RCS file: /projects/cvsroot/pgsql/src/Makefile,v
retrieving revision 1.42
diff -r1.42 Makefile
16a17,19
> ifeq ($(enable_dtrace), yes)
> 	$(DTRACE) -h -s $(top_builddir)/src/backend/utils/probes.d -o $(top_builddir)/src/include/probes.h
> endif
Index: src/backend/Makefile
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/Makefile,v
retrieving revision 1.125
diff -r1.125 Makefile
22a23
> ifeq ($(PORTNAME), solaris)
25a27
> endif
143a146
> ifeq ($(PORTNAME), solaris)
145a149
> endif
Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/transam/xact.c,v
retrieving revision 1.257
diff -r1.257 xact.c
1482c1482
< 	PG_TRACE1(transaction__start, vxid.localTransactionId);
---
> 	DATABASE_TRANSACTION_START(vxid.localTransactionId);
1607c1607
< 	PG_TRACE1(transaction__commit, MyProc->lxid);
---
> 	DATABASE_TRANSACTION_COMMIT(MyProc->lxid);
1993c1993
< 	PG_TRACE1(transaction__abort, MyProc->lxid);
---
> 	DATABASE_TRANSACTION_ABORT(MyProc->lxid);
Index: src/backend/storage/lmgr/lock.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/storage/lmgr/lock.c,v
retrieving revision 1.181
diff -r1.181 lock.c
790c790
< 		PG_TRACE2(lock__startwait, locktag->locktag_field2, lockmode);
---
> 		POSTGRESQL_LOCK_STARTWAIT(locktag->locktag_field2, lockmode);
794c794
< 		PG_TRACE2(lock__endwait, locktag->locktag_field2, lockmode);
---
> 		POSTGRESQL_LOCK_ENDWAIT(locktag->locktag_field2, lockmode);
Index: src/backend/storage/lmgr/lwlock.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/storage/lmgr/lwlock.c,v
retrieving revision 1.50
diff -r1.50 lwlock.c
450c450
< 		PG_TRACE2(lwlock__startwait, lockid, mode);
---
> 		POSTGRESQL_LWLOCK_STARTWAIT(lockid, mode);
461c461
< 		PG_TRACE2(lwlock__endwait, lockid, mode);
---
> 		POSTGRESQL_LWLOCK_ENDWAIT(lockid, mode);
472c472
< 	PG_TRACE2(lwlock__acquire, lockid, mode);
---
> 	POSTGRESQL_LWLOCK_ACQUIRE(lockid, mode);
543c543
< 		PG_TRACE2(lwlock__condacquire__fail, lockid, mode);
---
> 		POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(lockid, mode);
549c549
< 		PG_TRACE2(lwlock__condacquire, lockid, mode);
---
> 		POSTGRESQL_LWLOCK_CONDACQUIRE(lockid, mode);
634c634
< 	PG_TRACE1(lwlock__release, lockid);
---
> 	POSTGRESQL_LWLOCK_RELEASE(lockid);
Index: src/backend/utils/probes.d
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/utils/probes.d,v
retrieving revision 1.2
diff -r1.2 probes.d
10c10
< provider postgresql {
---
> provider database {
14a15,19
> 
> };
> 
> provider postgresql {
> 
Index: src/include/c.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/c.h,v
retrieving revision 1.222
diff -r1.222 c.h
60c60,64
< #include "pg_trace.h"
---
> #ifdef ENABLE_DTRACE
> #include "probes.h"
> #else
> #include "probes_null.h"
> #endif

#ifndef	_PROBES_NULL_H
#define	_PROBES_NULL_H

#define	POSTGRESQL_LOCK_ENDWAIT(arg0, arg1)
#define	POSTGRESQL_LOCK_ENDWAIT_ENABLED()

#define	POSTGRESQL_LOCK_STARTWAIT(arg0, arg1)
#define	POSTGRESQL_LOCK_STARTWAIT_ENABLED()

#define	POSTGRESQL_LWLOCK_ACQUIRE(arg0, arg1)
#define	POSTGRESQL_LWLOCK_ACQUIRE_ENABLED()

#define	POSTGRESQL_LWLOCK_CONDACQUIRE(arg0, arg1)
#define	POSTGRESQL_LWLOCK_CONDACQUIRE_ENABLED()

#define	POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(arg0, arg1)
#define	POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL_ENABLED()

#define	POSTGRESQL_LWLOCK_ENDWAIT(arg0, arg1)
#define	POSTGRESQL_LWLOCK_ENDWAIT_ENABLED()

#define	POSTGRESQL_LWLOCK_RELEASE(arg0)
#define	POSTGRESQL_LWLOCK_RELEASE_ENABLED()

#define	POSTGRESQL_LWLOCK_STARTWAIT(arg0, arg1)
#define	POSTGRESQL_LWLOCK_STARTWAIT_ENABLED()

#define	DATABASE_TRANSACTION_ABORT(arg0)
#define	DATABASE_TRANSACTION_ABORT_ENABLED()

#define	DATABASE_TRANSACTION_COMMIT(arg0)
#define	DATABASE_TRANSACTION_COMMIT_ENABLED()

#define	DATABASE_TRANSACTION_START(arg0)
#define	DATABASE_TRANSACTION_START_ENABLED()

#endif	/* _PROBES_NULL_H */