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Fix miserable coding in pg_stat_get_activity(). 

Commit dd1a3bccc replaced a test on whether a subroutine returned a
null pointer with a test on whether &pointer->backendStatus was null.
This accidentally failed to fail, at least on common compilers, because
backendStatus is the first field in the struct; but it was surely trouble
waiting to happen.  Commit f91feba87 then messed things up further,
changing the logic to

	local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
	if (!local_beentry)
		continue;
	beentry = &local_beentry->backendStatus;
	if (!beentry)
	{

where the second "if" is now dead code, so that the intended behavior of
printing a row with "<backend information not available>" cannot occur.

I suspect this is all moot because pgstat_fetch_stat_local_beentry
will never actually return null in this function's usage, but it's still
very poor coding.  Repair back to 9.4 where the original problem was
introduced.
This commit is contained in:
Tom Lane 2016-09-10 13:49:04 -04:00
parent 24992c6db9
commit ddc8893179
1 changed files with 11 additions and 15 deletions
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26
src/backend/utils/adt/pgstatfuncs.c
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@ -688,27 +688,17 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
MemSet(values, 0, sizeof(values));
MemSet(nulls, 0, sizeof(nulls));
if (pid != -1)
{
/* Skip any which are not the one we're looking for. */
PgBackendStatus *be = pgstat_fetch_stat_beentry(curr_backend);
if (!be || be->st_procpid != pid)
continue;
}
/* Get the next one in the list */
local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
if (!local_beentry)
continue;
beentry = &local_beentry->backendStatus;
if (!beentry)
{
int i;
for (i = 0; i < sizeof(nulls) / sizeof(nulls[0]); i++)
/* Ignore missing entries if looking for specific PID */
if (pid != -1)
continue;
for (i = 0; i < lengthof(nulls); i++)
nulls[i] = true;
nulls[5] = false;
@ -718,6 +708,12 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
continue;
}
beentry = &local_beentry->backendStatus;
/* If looking for specific PID, ignore all the others */
if (pid != -1 && beentry->st_procpid != pid)
continue;
/* Values available to all callers */
values[0] = ObjectIdGetDatum(beentry->st_databaseid);
values[1] = Int32GetDatum(beentry->st_procpid);