On 12/4/23 05:50, Tom Lane wrote:
Peter Eisentraut <pe...@eisentraut.org> writes:
src/backend/nodes/print.c contains a number of functions that print node
types, mostly to stdout. Most of these are not actually used anywhere
in the code. Are they meant to be inserted into the code ad hoc for
debugging? Is anyone using these?
Personally, I use pprint() a lot. (I invoke it manually from gdb and
then look into the postmaster log for results.) Its cousins such as
format_node_dump look like they were added by people with slightly
different tastes in output format, so they probably have a
constituency somewhere.
I tend to agree that print_rt() and the other tree-printing routines
below it (down to, but not including, print_slot) are not as useful
as invoking the outfuncs.c code; but others might think differently.
Sometimes you don't want all the gory detail.
I've wondered about these functions for years. I use pprint a lot, and I've wanted to use
print_slot/print_rt/print_tl (especially print_slot), but they never seemed to do anything. For
instance debugging `SELECT 1;`:
(gdb) b ExecResult
Breakpoint 1 at 0x5fcc25f1ffcb: file nodeResult.c, line 68.
(gdb) c
Continuing.
Breakpoint 1, ExecResult (pstate=0x5fcc285272f8) at nodeResult.c:68
68 {
(gdb) call print_rt(((PlannedStmt *)pstate->plan)->rtable)
(gdb) call print_slot(pstate->ps_ResultTupleSlot)
(gdb)
Even with log_min_messages and client_min_messages set to DEBUG5, nothing appears in psql or the log
or gdb. How are you supposed to use these functions?
Or if you want a real table, I still see no output after `ExecScanFetch` with:
create table s(i) as select generate_series(1,10);
select i from s;
I even tried dup'ing the backend's stdout to a file, but still got nothing:
(gdb) call creat("/tmp/pgout", 0600)
$1 = 103
(gdb) call dup2(103, 1)
'dup2' has unknown return type; cast the call to its declared return type
(gdb) call (int)dup2(103, 1)
$2 = 1
(gdb) b ExecScanFetch
Breakpoint 1 at 0x5fcc25ef026e: file execScan.c, line 37.
(gdb) c
Continuing.
Breakpoint 1, ExecScanFetch (node=node@entry=0x5fcc2852d348,
accessMtd=accessMtd@entry=0x5fcc25f20b74 <SeqNext>, recheckMtd=recheckMtd@entry=0x5fcc25f20b28
<SeqRecheck>) at execScan.c:37
37 {
(gdb) fin
Run till exit from #0 ExecScanFetch (node=node@entry=0x5fcc2852d348,
accessMtd=accessMtd@entry=0x5fcc25f20b74 <SeqNext>, recheckMtd=recheckMtd@entry=0x5fcc25f20b28
<SeqRecheck>) at execScan.c:37
0x00005fcc25ef044a in ExecScan (node=0x5fcc2852d348, accessMtd=accessMtd@entry=0x5fcc25f20b74
<SeqNext>, recheckMtd=recheckMtd@entry=0x5fcc25f20b28 <SeqRecheck>) at execScan.c:180
180 return ExecScanFetch(node, accessMtd, recheckMtd);
Value returned is $3 = (TupleTableSlot *) 0x5fcc2852d538
(gdb) call print_slot($3)
(gdb)
Yours,
--
Paul ~{:-)
p...@illuminatedcomputing.com
